| Message ID | 20171221134842.31287-2-brgl@bgdev.pl |
|---|---|
| State | Superseded |
| Delegated to: | Bartosz Golaszewski |
| Headers | show |
| Series | eeprom: at24: device tree support fixes | expand |
On Thu, Dec 21, 2017 at 3:48 PM, Bartosz Golaszewski <brgl@bgdev.pl> wrote: > Current description of the compatible property for at24 is quite vague. > > Specify an exact list of accepted compatibles and document the - now > deprecated - strings which were previously used in device tree files. > + will still work, but are now deprecated. I would rather reprase it to make people not think that's okay to still use deprecated strings. Something like "are now deprecated, please do not use in new code or drivers". Supporting old but deprecated is implied by DT globally. (We don't break user space, remember?)
On 2017-12-21 14:48, Bartosz Golaszewski wrote: > Current description of the compatible property for at24 is quite vague. > > Specify an exact list of accepted compatibles and document the - now > deprecated - strings which were previously used in device tree files. Why is it suddenly deprecated to correctly specify what hardware you have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. Sure, it happens to be compatible with "atmel,24c32", but that is supposed to be written with a fallback as "nxp,24c32", "atmel,24c32" if I understand correctly. So, why is that deprecated in this case? What if (a few years down the line) it is discovered that some weird quirk is needed that is only appropriate for nxp chips? nxp is of course just an example, pick any manufacturer of eeproms (supposedly) compatible with the atmel interface. Cheers, Peter
On 12/21/2017 10:20 AM, Peter Rosin wrote: > On 2017-12-21 14:48, Bartosz Golaszewski wrote: >> Current description of the compatible property for at24 is quite vague. >> >> Specify an exact list of accepted compatibles and document the - now >> deprecated - strings which were previously used in device tree files. > > Why is it suddenly deprecated to correctly specify what hardware you > have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. > Sure, it happens to be compatible with "atmel,24c32", but that is > supposed to be written with a fallback as > > "nxp,24c32", "atmel,24c32" > > if I understand correctly. So, why is that deprecated in this case? > > What if (a few years down the line) it is discovered that some weird > quirk is needed that is only appropriate for nxp chips? > > nxp is of course just an example, pick any manufacturer of eeproms > (supposedly) compatible with the atmel interface. > So now I am supposed to change my device tree from "microchip,24c128" to "atmel,24c128"? Also, at,24c08 is listed in Documentation/devicetree/bindings/trivial-devices.txt. It should probably be removed.
On 12/21/2017 11:24 AM, David Lechner wrote: > Also, at,24c08 is listed in > Documentation/devicetree/bindings/trivial-devices.txt. It should > probably be removed. And st,24c256
Hello Peter, On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: > On 2017-12-21 14:48, Bartosz Golaszewski wrote: >> Current description of the compatible property for at24 is quite vague. >> >> Specify an exact list of accepted compatibles and document the - now >> deprecated - strings which were previously used in device tree files. > > Why is it suddenly deprecated to correctly specify what hardware you > have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. Sorry but I disagree. When you specify a compatible string, you are not specifying a particular hardware but a device programming model. It's very common to use a compatible string that doesn't match exactly the specific hardware used. That's why it's called _compatible_ BTW. For example when a DTS define a UART node with an ns16550 compatible, they don't really mean that have a UART IC manufactured by National Semiconductor. > Sure, it happens to be compatible with "atmel,24c32", but that is > supposed to be written with a fallback as > > "nxp,24c32", "atmel,24c32" This isn't a requirement really, systems integrators are free to use more than one <manufacturer,model> tuple in the compatible string if they want the DTB to be future proof, just in case there's a need for a more specific driver or if the programming model happened to not be the same at the end. This is usually done for the boards compatible string as an example, even when there isn't a struct machine_desc for the specific board compatible and only for the SoC family. So it's OK if you want to define the compatible as "nxp,24c32", "atmel,24c32", but that's a general OF concept and not something related to the at24 eeprom driver so I'm not sure if it should be mentioned in the at24 DT binding doc. > if I understand correctly. So, why is that deprecated in this case? > > What if (a few years down the line) it is discovered that some weird > quirk is needed that is only appropriate for nxp chips? > > nxp is of course just an example, pick any manufacturer of eeproms > (supposedly) compatible with the atmel interface. > That's indeed a possibility and the reason why most DT nodes have a more specific <manufacturer,model> before the generic one matched by drivers. I really doubt that in the future it will be found that a more specific compatible string is needed for one manufacturer in this case, specially since the driver didn't even care about the manufacturers until recently. So I think that makes no sense for a driver to support all possible manufacturers as possible compatible strings if all the devices have the same exact programming model. > Cheers, > Peter Best regards, Javier
On 2017-12-21 21:27, Javier Martinez Canillas wrote: > Hello Peter, > > On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: >> On 2017-12-21 14:48, Bartosz Golaszewski wrote: >>> Current description of the compatible property for at24 is quite vague. >>> >>> Specify an exact list of accepted compatibles and document the - now >>> deprecated - strings which were previously used in device tree files. >> >> Why is it suddenly deprecated to correctly specify what hardware you >> have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. > > Sorry but I disagree. > > When you specify a compatible string, you are not specifying a > particular hardware but a device programming model. That's not what it says in https://elinux.org/Device_Tree_Usage in the "Understanding the compatible Property" section. I quote: compatible is a list of strings. The first string in the list specifies the exact device that the node represents in the form "<manufacturer>,<model>". The following strings represent other devices that the device is compatible with. Pretty clearly talks about devices and not programming models. But maybe I shouldn't trust that reference? What should I be reading instead? > It's very common to use a compatible string that doesn't match exactly > the specific hardware used. That's why it's called _compatible_ BTW. That's not how I read the above. > For example when a DTS define a UART node with an ns16550 compatible, > they don't really mean that have a UART IC manufactured by National > Semiconductor. That just tells me that most people are a little bit lazy and ready to cut a corner or two when they can get away with it. Or that there is some form of misunderstanding at work... >> Sure, it happens to be compatible with "atmel,24c32", but that is >> supposed to be written with a fallback as >> >> "nxp,24c32", "atmel,24c32" > > This isn't a requirement really, systems integrators are free to use > more than one <manufacturer,model> tuple in the compatible string if > they want the DTB to be future proof, just in case there's a need for > a more specific driver or if the programming model happened to not be > the same at the end. This is usually done for the boards compatible > string as an example, even when there isn't a struct machine_desc for > the specific board compatible and only for the SoC family. > > So it's OK if you want to define the compatible as "nxp,24c32", > "atmel,24c32", but that's a general OF concept and not something > related to the at24 eeprom driver so I'm not sure if it should be > mentioned in the at24 DT binding doc. One problem is that if "nxp,24c32" (or "nxp,24c02" as in the example below) is not a valid compatible, the tooling will be correct to complain about it. Currently, it is just a checkpatch deficiency that it complains like this: $ scripts/checkpatch.pl -f arch/arm/boot/dts/at91-tse850-3.dts WARNING: DT compatible string "nxp,24c02" appears un-documented -- check ./Documentation/devicetree/bindings/ #249: FILE: arch/arm/boot/dts/at91-tse850-3.dts:249: + compatible = "nxp,24c02", "atmel,24c02"; >> if I understand correctly. So, why is that deprecated in this case? >> >> What if (a few years down the line) it is discovered that some weird >> quirk is needed that is only appropriate for nxp chips? >> >> nxp is of course just an example, pick any manufacturer of eeproms >> (supposedly) compatible with the atmel interface. >> > > That's indeed a possibility and the reason why most DT nodes have a > more specific <manufacturer,model> before the generic one matched by > drivers. I really doubt that in the future it will be found that a > more specific compatible string is needed for one manufacturer in this > case, specially since the driver didn't even care about the > manufacturers until recently. I'm not talking about the driver. But if what you say is true, that change would have broken a number of existing DTBs. Is that really the case? > So I think that makes no sense for a driver to support all possible > manufacturers as possible compatible strings if all the devices have > the same exact programming model. That's what the fallback is for. With that in place the driver can start to care when there is a need but until then it can work just as it always has. Without knowing the specific device, the driver has less chance to adapt when the unexpected is discovered. But again, I'm not really discussing driver details, I'm complaining about the proposed changes to the bindings. I simply don't see how they make sense. Cheers, Peter
Hello Peter, On Fri, Dec 22, 2017 at 12:07 AM, Peter Rosin <peda@axentia.se> wrote: > On 2017-12-21 21:27, Javier Martinez Canillas wrote: >> Hello Peter, >> >> On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: >>> On 2017-12-21 14:48, Bartosz Golaszewski wrote: >>>> Current description of the compatible property for at24 is quite vague. >>>> >>>> Specify an exact list of accepted compatibles and document the - now >>>> deprecated - strings which were previously used in device tree files. >>> >>> Why is it suddenly deprecated to correctly specify what hardware you >>> have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. >> >> Sorry but I disagree. >> >> When you specify a compatible string, you are not specifying a >> particular hardware but a device programming model. > > That's not what it says in https://elinux.org/Device_Tree_Usage I think the most up-to-date DT reference is at: https://www.devicetree.org/ > in the "Understanding the compatible Property" section. I quote: > > compatible is a list of strings. The first string in the > list specifies the exact device that the node represents > in the form "<manufacturer>,<model>". The following strings > represent other devices that the device is compatible with. > > Pretty clearly talks about devices and not programming models. But > maybe I shouldn't trust that reference? What should I be reading > instead? > For example the latest spec draft (https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2-rc1/devicetree-specification-v0.2-rc1.pdf) says: "The compatible property value consists of one or more strings that define the specific programming model for the device. This list of strings should be used by a client program for device driver selection. The property value consists of a concatenated list of null terminated strings, from most specific to most general. They allow a device to express its compatibility with a family of similar devices, potentially allowing a single device driver to match against several devices." The recommended format is "manufacturer,model", where manufacturer is a string describing the name of the manufacturer (such as a stock ticker symbol), and model specifies the model number." Example: compatible = "fsl,mpc8641", "ns16550"; In this example, an operating system would first try to locate a device driver that supported fsl,mpc8641. If a driver was not found, it would then try to locate a driver that supported the more general ns16550 device type." >> It's very common to use a compatible string that doesn't match exactly >> the specific hardware used. That's why it's called _compatible_ BTW. > > That's not how I read the above. > That's not how I read it nor my experience with DT, but of course I may be wrong on this. >> For example when a DTS define a UART node with an ns16550 compatible, >> they don't really mean that have a UART IC manufactured by National >> Semiconductor. > > That just tells me that most people are a little bit lazy and ready > to cut a corner or two when they can get away with it. Or that there > is some form of misunderstanding at work... > For example, I usually see that different SoC families from the same vendor use the same compatible string for integrated peripherals just because are the same from a programming model point of view. TI am33xx SoCs use a lot of omap3 compatible strings on their nodes and its similar on Exynos SoCs which are the two ARM SoCs I'm most familiar with. Following your logic that's wrong and instead a new compatible string should be added for the GPIO or pinctrl drivers even when are the same because refer to different devices. >>> Sure, it happens to be compatible with "atmel,24c32", but that is >>> supposed to be written with a fallback as >>> >>> "nxp,24c32", "atmel,24c32" >> >> This isn't a requirement really, systems integrators are free to use >> more than one <manufacturer,model> tuple in the compatible string if >> they want the DTB to be future proof, just in case there's a need for >> a more specific driver or if the programming model happened to not be >> the same at the end. This is usually done for the boards compatible >> string as an example, even when there isn't a struct machine_desc for >> the specific board compatible and only for the SoC family. >> >> So it's OK if you want to define the compatible as "nxp,24c32", >> "atmel,24c32", but that's a general OF concept and not something >> related to the at24 eeprom driver so I'm not sure if it should be >> mentioned in the at24 DT binding doc. > > One problem is that if "nxp,24c32" (or "nxp,24c02" as in the example > below) is not a valid compatible, the tooling will be correct to > complain about it. Currently, it is just a checkpatch deficiency that > it complains like this: > > $ scripts/checkpatch.pl -f arch/arm/boot/dts/at91-tse850-3.dts > WARNING: DT compatible string "nxp,24c02" appears un-documented -- check ./Documentation/devicetree/bindings/ > #249: FILE: arch/arm/boot/dts/at91-tse850-3.dts:249: > + compatible = "nxp,24c02", "atmel,24c02"; > But isn't that a bug in checkpatch? as long as there's a valid <manufacturer,model> tuple in the compatible string, it shouldn't complain. >>> if I understand correctly. So, why is that deprecated in this case? >>> >>> What if (a few years down the line) it is discovered that some weird >>> quirk is needed that is only appropriate for nxp chips? >>> >>> nxp is of course just an example, pick any manufacturer of eeproms >>> (supposedly) compatible with the atmel interface. >>> >> >> That's indeed a possibility and the reason why most DT nodes have a >> more specific <manufacturer,model> before the generic one matched by >> drivers. I really doubt that in the future it will be found that a >> more specific compatible string is needed for one manufacturer in this >> case, specially since the driver didn't even care about the >> manufacturers until recently. > > I'm not talking about the driver. But if what you say is true, that > change would have broken a number of existing DTBs. Is that really the > case? > Sorry, I didn't get which change you meant. >> So I think that makes no sense for a driver to support all possible >> manufacturers as possible compatible strings if all the devices have >> the same exact programming model. > > That's what the fallback is for. With that in place the driver can > start to care when there is a need but until then it can work just > as it always has. Without knowing the specific device, the driver has > less chance to adapt when the unexpected is discovered. But again, > I'm not really discussing driver details, I'm complaining about the > proposed changes to the bindings. I simply don't see how they make > sense. > My point is that saying in a DT binding that you could have a more specific <manufacturer,model> followed by a generic one is redundant. That's already something one can do to make the DT future proof and latter if is found that the more specific pair is needed, then compatible can be added to the OF device ID table making the driver to match that an the <manufacturer,model> added to the DT binding making it formal. That's my understanding at least, but I could be completely wrong too since I'm not a DT expert. > Cheers, > Peter Best regards, Javier
On 2017-12-22 00:38, Javier Martinez Canillas wrote: > Hello Peter, > > On Fri, Dec 22, 2017 at 12:07 AM, Peter Rosin <peda@axentia.se> wrote: >> On 2017-12-21 21:27, Javier Martinez Canillas wrote: >>> Hello Peter, >>> >>> On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: >>>> On 2017-12-21 14:48, Bartosz Golaszewski wrote: >>>>> Current description of the compatible property for at24 is quite vague. >>>>> >>>>> Specify an exact list of accepted compatibles and document the - now >>>>> deprecated - strings which were previously used in device tree files. >>>> >>>> Why is it suddenly deprecated to correctly specify what hardware you >>>> have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. >>> >>> Sorry but I disagree. >>> >>> When you specify a compatible string, you are not specifying a >>> particular hardware but a device programming model. >> >> That's not what it says in https://elinux.org/Device_Tree_Usage > > I think the most up-to-date DT reference is at: > > https://www.devicetree.org/ > >> in the "Understanding the compatible Property" section. I quote: >> >> compatible is a list of strings. The first string in the >> list specifies the exact device that the node represents >> in the form "<manufacturer>,<model>". The following strings >> represent other devices that the device is compatible with. >> >> Pretty clearly talks about devices and not programming models. But >> maybe I shouldn't trust that reference? What should I be reading >> instead? >> > > For example the latest spec draft > (https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2-rc1/devicetree-specification-v0.2-rc1.pdf) > says: > > "The compatible property value consists of one or more strings that > define the specific programming model for the device. This list of > strings should be used by a client program for device driver > selection. The property value consists of a concatenated list of null > terminated strings, from most specific to most general. They allow a > device to express its compatibility with a family of similar devices, > potentially allowing a single device driver to match against several > devices." > > The recommended format is "manufacturer,model", where manufacturer is > a string describing the name of the manufacturer (such as a stock > ticker symbol), and model specifies the model number." > > Example: > > compatible = "fsl,mpc8641", "ns16550"; > > In this example, an operating system would first try to locate a > device driver that supported fsl,mpc8641. If a driver was not found, > it would then try to locate a driver that supported the more general > ns16550 device type." Yes, that's a bit different from the wording on the elinux site. Thanks for the pointer! Google was not my friend on this occasion, since I managed to miss that site in my searches. Maybe it has gotten a higher rank now that 0.2 is out, because now I find it easily? >>> It's very common to use a compatible string that doesn't match exactly >>> the specific hardware used. That's why it's called _compatible_ BTW. >> >> That's not how I read the above. >> > > That's not how I read it nor my experience with DT, but of course I > may be wrong on this. Either way, it should not be wrong to specify the more specific binding before the generic fallback, as is done in the at91-tse850-3.dts example I gave below. >>> For example when a DTS define a UART node with an ns16550 compatible, >>> they don't really mean that have a UART IC manufactured by National >>> Semiconductor. >> >> That just tells me that most people are a little bit lazy and ready >> to cut a corner or two when they can get away with it. Or that there >> is some form of misunderstanding at work... >> > > For example, I usually see that different SoC families from the same > vendor use the same compatible string for integrated peripherals just > because are the same from a programming model point of view. > > TI am33xx SoCs use a lot of omap3 compatible strings on their nodes > and its similar on Exynos SoCs which are the two ARM SoCs I'm most > familiar with. Following your logic that's wrong and instead a new > compatible string should be added for the GPIO or pinctrl drivers even > when are the same because refer to different devices. Considering the above quote from the actual DT spec, I wouldn't say wrong. But I'd still say that it should be preferred to list the actual device before the fallback to some generic programming model compatible or some previous version of the hardware/IP-block. Just in case an unintended difference is discovered late in the game... >>>> Sure, it happens to be compatible with "atmel,24c32", but that is >>>> supposed to be written with a fallback as >>>> >>>> "nxp,24c32", "atmel,24c32" >>> >>> This isn't a requirement really, systems integrators are free to use >>> more than one <manufacturer,model> tuple in the compatible string if >>> they want the DTB to be future proof, just in case there's a need for >>> a more specific driver or if the programming model happened to not be >>> the same at the end. This is usually done for the boards compatible >>> string as an example, even when there isn't a struct machine_desc for >>> the specific board compatible and only for the SoC family. >>> >>> So it's OK if you want to define the compatible as "nxp,24c32", >>> "atmel,24c32", but that's a general OF concept and not something >>> related to the at24 eeprom driver so I'm not sure if it should be >>> mentioned in the at24 DT binding doc. >> >> One problem is that if "nxp,24c32" (or "nxp,24c02" as in the example >> below) is not a valid compatible, the tooling will be correct to >> complain about it. Currently, it is just a checkpatch deficiency that >> it complains like this: >> >> $ scripts/checkpatch.pl -f arch/arm/boot/dts/at91-tse850-3.dts >> WARNING: DT compatible string "nxp,24c02" appears un-documented -- check ./Documentation/devicetree/bindings/ >> #249: FILE: arch/arm/boot/dts/at91-tse850-3.dts:249: >> + compatible = "nxp,24c02", "atmel,24c02"; >> > > But isn't that a bug in checkpatch? as long as there's a valid > <manufacturer,model> tuple in the compatible string, it shouldn't > complain. Then there is a significant risk that speeling mistakes are not caught. So, I don't think it will be considered a bug unless a DT guru says so of course. I think the checkpatch intention is to catch all undocumented compatibles. But I don't know of course... >>>> if I understand correctly. So, why is that deprecated in this case? >>>> >>>> What if (a few years down the line) it is discovered that some weird >>>> quirk is needed that is only appropriate for nxp chips? >>>> >>>> nxp is of course just an example, pick any manufacturer of eeproms >>>> (supposedly) compatible with the atmel interface. >>>> >>> >>> That's indeed a possibility and the reason why most DT nodes have a >>> more specific <manufacturer,model> before the generic one matched by >>> drivers. I really doubt that in the future it will be found that a >>> more specific compatible string is needed for one manufacturer in this >>> case, specially since the driver didn't even care about the >>> manufacturers until recently. >> >> I'm not talking about the driver. But if what you say is true, that >> change would have broken a number of existing DTBs. Is that really the >> case? >> > > Sorry, I didn't get which change you meant. I meant whatever change you implied with "the driver didn't even care about the manufacturers until recently". However, on second reading it may be the case that "care" did not imply that a breaking change was made, that was however my interpretation. Oh well... >>> So I think that makes no sense for a driver to support all possible >>> manufacturers as possible compatible strings if all the devices have >>> the same exact programming model. >> >> That's what the fallback is for. With that in place the driver can >> start to care when there is a need but until then it can work just >> as it always has. Without knowing the specific device, the driver has >> less chance to adapt when the unexpected is discovered. But again, >> I'm not really discussing driver details, I'm complaining about the >> proposed changes to the bindings. I simply don't see how they make >> sense. >> > > My point is that saying in a DT binding that you could have a more > specific <manufacturer,model> followed by a generic one is redundant. > That's already something one can do to make the DT future proof and > latter if is found that the more specific pair is needed, then > compatible can be added to the OF device ID table making the driver to > match that an the <manufacturer,model> added to the DT binding making > it formal. > > That's my understanding at least, but I could be completely wrong too > since I'm not a DT expert. My understanding is that in order to do that future proofing, you first have to document the more specific binding. Note that documenting the more specific binding will not add any burden whatsoever to the driver, as long as the fallback is in place, at least until a difference between the specific and the generic device or programming model is discovered... So, until you need to use the specific compatible, it is pure documentation overhead. This 1/5 patch deprecates the more specific bindings, and that seems to be the wrong direction. *More* of the specific compatibles should be encouraged (and documented) instead of less. But what do I know? Anyway, I'll shut up now, I think I've made my point... Cheers, Peter
On Fri, Dec 22, 2017 at 05:58:29PM +0100, Peter Rosin wrote: > On 2017-12-22 00:38, Javier Martinez Canillas wrote: > > Hello Peter, > > > > On Fri, Dec 22, 2017 at 12:07 AM, Peter Rosin <peda@axentia.se> wrote: > >> On 2017-12-21 21:27, Javier Martinez Canillas wrote: > >>> Hello Peter, > >>> > >>> On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: > >>>> On 2017-12-21 14:48, Bartosz Golaszewski wrote: > >>>>> Current description of the compatible property for at24 is quite vague. > >>>>> > >>>>> Specify an exact list of accepted compatibles and document the - now > >>>>> deprecated - strings which were previously used in device tree files. > >>>> > >>>> Why is it suddenly deprecated to correctly specify what hardware you > >>>> have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. > >>> > >>> Sorry but I disagree. > >>> > >>> When you specify a compatible string, you are not specifying a > >>> particular hardware but a device programming model. > >> > >> That's not what it says in https://elinux.org/Device_Tree_Usage > > > > I think the most up-to-date DT reference is at: > > > > https://www.devicetree.org/ > > > >> in the "Understanding the compatible Property" section. I quote: > >> > >> compatible is a list of strings. The first string in the > >> list specifies the exact device that the node represents > >> in the form "<manufacturer>,<model>". The following strings > >> represent other devices that the device is compatible with. > >> > >> Pretty clearly talks about devices and not programming models. But > >> maybe I shouldn't trust that reference? What should I be reading > >> instead? > >> > > > > For example the latest spec draft > > (https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2-rc1/devicetree-specification-v0.2-rc1.pdf) > > says: > > > > "The compatible property value consists of one or more strings that > > define the specific programming model for the device. This list of > > strings should be used by a client program for device driver > > selection. The property value consists of a concatenated list of null > > terminated strings, from most specific to most general. They allow a > > device to express its compatibility with a family of similar devices, > > potentially allowing a single device driver to match against several > > devices." > > > > The recommended format is "manufacturer,model", where manufacturer is > > a string describing the name of the manufacturer (such as a stock > > ticker symbol), and model specifies the model number." > > > > Example: > > > > compatible = "fsl,mpc8641", "ns16550"; > > > > In this example, an operating system would first try to locate a > > device driver that supported fsl,mpc8641. If a driver was not found, > > it would then try to locate a driver that supported the more general > > ns16550 device type." > > Yes, that's a bit different from the wording on the elinux site. Thanks > for the pointer! Google was not my friend on this occasion, since I > managed to miss that site in my searches. Maybe it has gotten a higher > rank now that 0.2 is out, because now I find it easily? The wording may be different, but both (and Peter) are correct. And ns16550 is a perfect example of why that string alone is not sufficient. Just go count the number of variants and quirks in the kernel 8250 driver. > >>> It's very common to use a compatible string that doesn't match exactly > >>> the specific hardware used. That's why it's called _compatible_ BTW. > >> > >> That's not how I read the above. > >> > > > > That's not how I read it nor my experience with DT, but of course I > > may be wrong on this. > > Either way, it should not be wrong to specify the more specific binding > before the generic fallback, as is done in the at91-tse850-3.dts > example I gave below. Indeed. I don't think I've ever said anyone is being too specific. > >>> For example when a DTS define a UART node with an ns16550 compatible, > >>> they don't really mean that have a UART IC manufactured by National > >>> Semiconductor. > >> > >> That just tells me that most people are a little bit lazy and ready > >> to cut a corner or two when they can get away with it. Or that there > >> is some form of misunderstanding at work... > >> > > > > For example, I usually see that different SoC families from the same > > vendor use the same compatible string for integrated peripherals just > > because are the same from a programming model point of view. > > > > TI am33xx SoCs use a lot of omap3 compatible strings on their nodes > > and its similar on Exynos SoCs which are the two ARM SoCs I'm most > > familiar with. Following your logic that's wrong and instead a new > > compatible string should be added for the GPIO or pinctrl drivers even > > when are the same because refer to different devices. > > Considering the above quote from the actual DT spec, I wouldn't say wrong. > But I'd still say that it should be preferred to list the actual device > before the fallback to some generic programming model compatible or some > previous version of the hardware/IP-block. Just in case an unintended > difference is discovered late in the game... Let me clear, "generic" compatibles alone are wrong. > > >>>> Sure, it happens to be compatible with "atmel,24c32", but that is > >>>> supposed to be written with a fallback as > >>>> > >>>> "nxp,24c32", "atmel,24c32" > >>> > >>> This isn't a requirement really, systems integrators are free to use > >>> more than one <manufacturer,model> tuple in the compatible string if > >>> they want the DTB to be future proof, just in case there's a need for > >>> a more specific driver or if the programming model happened to not be > >>> the same at the end. This is usually done for the boards compatible > >>> string as an example, even when there isn't a struct machine_desc for > >>> the specific board compatible and only for the SoC family. > >>> > >>> So it's OK if you want to define the compatible as "nxp,24c32", > >>> "atmel,24c32", but that's a general OF concept and not something > >>> related to the at24 eeprom driver so I'm not sure if it should be > >>> mentioned in the at24 DT binding doc. > >> > >> One problem is that if "nxp,24c32" (or "nxp,24c02" as in the example > >> below) is not a valid compatible, the tooling will be correct to > >> complain about it. Currently, it is just a checkpatch deficiency that > >> it complains like this: > >> > >> $ scripts/checkpatch.pl -f arch/arm/boot/dts/at91-tse850-3.dts > >> WARNING: DT compatible string "nxp,24c02" appears un-documented -- check ./Documentation/devicetree/bindings/ > >> #249: FILE: arch/arm/boot/dts/at91-tse850-3.dts:249: > >> + compatible = "nxp,24c02", "atmel,24c02"; > >> > > > > But isn't that a bug in checkpatch? as long as there's a valid > > <manufacturer,model> tuple in the compatible string, it shouldn't > > complain. > > Then there is a significant risk that speeling mistakes are not > caught. So, I don't think it will be considered a bug unless a DT > guru says so of course. I think the checkpatch intention is to catch > all undocumented compatibles. But I don't know of course... checkpatch.pl is just plain stupid. Who wrote that check anyway? Because bindings are not machine parseable, compatible string checks are pretty much just a grep for the string in all binding docs. So "The" or "compatible" would be valid compatible strings for checkpatch.pl. If you want to quiet checkpatch.pl, I'd suggest documenting compatible strings as "<vendor>,foo" and having checkpatch match any string for <vendor>. We already handle vendor,<soc>-block type compatible descriptions. Rob
2017-12-26 22:32 GMT+01:00 Rob Herring <robh@kernel.org>: > On Fri, Dec 22, 2017 at 05:58:29PM +0100, Peter Rosin wrote: >> On 2017-12-22 00:38, Javier Martinez Canillas wrote: >> > Hello Peter, >> > >> > On Fri, Dec 22, 2017 at 12:07 AM, Peter Rosin <peda@axentia.se> wrote: >> >> On 2017-12-21 21:27, Javier Martinez Canillas wrote: >> >>> Hello Peter, >> >>> >> >>> On Thu, Dec 21, 2017 at 5:20 PM, Peter Rosin <peda@axentia.se> wrote: >> >>>> On 2017-12-21 14:48, Bartosz Golaszewski wrote: >> >>>>> Current description of the compatible property for at24 is quite vague. >> >>>>> >> >>>>> Specify an exact list of accepted compatibles and document the - now >> >>>>> deprecated - strings which were previously used in device tree files. >> >>>> >> >>>> Why is it suddenly deprecated to correctly specify what hardware you >> >>>> have, e.g. "nxp,24c32". In this case the manufacturer is nxp, damnit. >> >>> >> >>> Sorry but I disagree. >> >>> >> >>> When you specify a compatible string, you are not specifying a >> >>> particular hardware but a device programming model. >> >> >> >> That's not what it says in https://elinux.org/Device_Tree_Usage >> > >> > I think the most up-to-date DT reference is at: >> > >> > https://www.devicetree.org/ >> > >> >> in the "Understanding the compatible Property" section. I quote: >> >> >> >> compatible is a list of strings. The first string in the >> >> list specifies the exact device that the node represents >> >> in the form "<manufacturer>,<model>". The following strings >> >> represent other devices that the device is compatible with. >> >> >> >> Pretty clearly talks about devices and not programming models. But >> >> maybe I shouldn't trust that reference? What should I be reading >> >> instead? >> >> >> > >> > For example the latest spec draft >> > (https://github.com/devicetree-org/devicetree-specification/releases/download/v0.2-rc1/devicetree-specification-v0.2-rc1.pdf) >> > says: >> > >> > "The compatible property value consists of one or more strings that >> > define the specific programming model for the device. This list of >> > strings should be used by a client program for device driver >> > selection. The property value consists of a concatenated list of null >> > terminated strings, from most specific to most general. They allow a >> > device to express its compatibility with a family of similar devices, >> > potentially allowing a single device driver to match against several >> > devices." >> > >> > The recommended format is "manufacturer,model", where manufacturer is >> > a string describing the name of the manufacturer (such as a stock >> > ticker symbol), and model specifies the model number." >> > >> > Example: >> > >> > compatible = "fsl,mpc8641", "ns16550"; >> > >> > In this example, an operating system would first try to locate a >> > device driver that supported fsl,mpc8641. If a driver was not found, >> > it would then try to locate a driver that supported the more general >> > ns16550 device type." >> >> Yes, that's a bit different from the wording on the elinux site. Thanks >> for the pointer! Google was not my friend on this occasion, since I >> managed to miss that site in my searches. Maybe it has gotten a higher >> rank now that 0.2 is out, because now I find it easily? > > The wording may be different, but both (and Peter) are correct. > > And ns16550 is a perfect example of why that string alone is not > sufficient. Just go count the number of variants and quirks in the > kernel 8250 driver. > >> >>> It's very common to use a compatible string that doesn't match exactly >> >>> the specific hardware used. That's why it's called _compatible_ BTW. >> >> >> >> That's not how I read the above. >> >> >> > >> > That's not how I read it nor my experience with DT, but of course I >> > may be wrong on this. >> >> Either way, it should not be wrong to specify the more specific binding >> before the generic fallback, as is done in the at91-tse850-3.dts >> example I gave below. > > Indeed. I don't think I've ever said anyone is being too specific. > >> >>> For example when a DTS define a UART node with an ns16550 compatible, >> >>> they don't really mean that have a UART IC manufactured by National >> >>> Semiconductor. >> >> >> >> That just tells me that most people are a little bit lazy and ready >> >> to cut a corner or two when they can get away with it. Or that there >> >> is some form of misunderstanding at work... >> >> >> > >> > For example, I usually see that different SoC families from the same >> > vendor use the same compatible string for integrated peripherals just >> > because are the same from a programming model point of view. >> > >> > TI am33xx SoCs use a lot of omap3 compatible strings on their nodes >> > and its similar on Exynos SoCs which are the two ARM SoCs I'm most >> > familiar with. Following your logic that's wrong and instead a new >> > compatible string should be added for the GPIO or pinctrl drivers even >> > when are the same because refer to different devices. >> >> Considering the above quote from the actual DT spec, I wouldn't say wrong. >> But I'd still say that it should be preferred to list the actual device >> before the fallback to some generic programming model compatible or some >> previous version of the hardware/IP-block. Just in case an unintended >> difference is discovered late in the game... > > Let me clear, "generic" compatibles alone are wrong. > >> >> >>>> Sure, it happens to be compatible with "atmel,24c32", but that is >> >>>> supposed to be written with a fallback as >> >>>> >> >>>> "nxp,24c32", "atmel,24c32" >> >>> >> >>> This isn't a requirement really, systems integrators are free to use >> >>> more than one <manufacturer,model> tuple in the compatible string if >> >>> they want the DTB to be future proof, just in case there's a need for >> >>> a more specific driver or if the programming model happened to not be >> >>> the same at the end. This is usually done for the boards compatible >> >>> string as an example, even when there isn't a struct machine_desc for >> >>> the specific board compatible and only for the SoC family. >> >>> >> >>> So it's OK if you want to define the compatible as "nxp,24c32", >> >>> "atmel,24c32", but that's a general OF concept and not something >> >>> related to the at24 eeprom driver so I'm not sure if it should be >> >>> mentioned in the at24 DT binding doc. >> >> >> >> One problem is that if "nxp,24c32" (or "nxp,24c02" as in the example >> >> below) is not a valid compatible, the tooling will be correct to >> >> complain about it. Currently, it is just a checkpatch deficiency that >> >> it complains like this: >> >> >> >> $ scripts/checkpatch.pl -f arch/arm/boot/dts/at91-tse850-3.dts >> >> WARNING: DT compatible string "nxp,24c02" appears un-documented -- check ./Documentation/devicetree/bindings/ >> >> #249: FILE: arch/arm/boot/dts/at91-tse850-3.dts:249: >> >> + compatible = "nxp,24c02", "atmel,24c02"; >> >> >> > >> > But isn't that a bug in checkpatch? as long as there's a valid >> > <manufacturer,model> tuple in the compatible string, it shouldn't >> > complain. >> >> Then there is a significant risk that speeling mistakes are not >> caught. So, I don't think it will be considered a bug unless a DT >> guru says so of course. I think the checkpatch intention is to catch >> all undocumented compatibles. But I don't know of course... > > checkpatch.pl is just plain stupid. Who wrote that check anyway? Because > bindings are not machine parseable, compatible string checks are pretty > much just a grep for the string in all binding docs. So "The" or > "compatible" would be valid compatible strings for checkpatch.pl. > > If you want to quiet checkpatch.pl, I'd suggest documenting compatible > strings as "<vendor>,foo" and having checkpatch match any string for > <vendor>. We already handle vendor,<soc>-block type compatible > descriptions. > > Rob Hi Rob, more than shutting up checkpatch, I care about cleaning up the device tree support in at24 and extending it with other variants that are currently supported as i2c devices. While just listing the supported models with any vendor allowed would be fine in most cases, there are also examples like "renesas,r1ex24002" which is really just "atmel,24c02" but with a different model name. So should we say in the document that 'any "<manufacturer>,<model>" pair is allowed as long as the fallback is one of "atmel,<model>" strings'? Best regards, Bartosz Golaszewski
diff --git a/Documentation/devicetree/bindings/eeprom/at24.txt b/Documentation/devicetree/bindings/eeprom/at24.txt index cbc80e194ac6..16b687458b14 100644 --- a/Documentation/devicetree/bindings/eeprom/at24.txt +++ b/Documentation/devicetree/bindings/eeprom/at24.txt @@ -2,28 +2,32 @@ EEPROMs (I2C) Required properties: - - compatible : should be "<manufacturer>,<type>", like these: - - "atmel,24c00", "atmel,24c01", "atmel,24c02", "atmel,24c04", - "atmel,24c08", "atmel,24c16", "atmel,24c32", "atmel,24c64", - "atmel,24c128", "atmel,24c256", "atmel,24c512", "atmel,24c1024" - - "catalyst,24c32" - - "microchip,24c128" - - "ramtron,24c64" - - "renesas,r1ex24002" - - The following manufacturers values have been deprecated: - "at", "at24" - - If there is no specific driver for <manufacturer>, a generic - device with <type> and manufacturer "atmel" should be used. - Possible types are: - "24c00", "24c01", "24c02", "24c04", "24c08", "24c16", "24c32", "24c64", - "24c128", "24c256", "24c512", "24c1024", "spd" + - compatible: must be one of the following: + + "atmel,24c00", + "atmel,24c01", + "atmel,24c02", + "atmel,24c04", + "atmel,24c08", + "atmel,24c16", + "atmel,24c32", + "atmel,24c64", + "atmel,24c128", + "atmel,24c256", + "atmel,24c512", + "atmel,24c1024" + + NOTE: old compatible strings, such as: + + "catalyst,24c32", + "microchip,24c128", + "ramtron,24c64", + "renesas,r1ex24002", + "at,24c08", + "at24,24c08", + "24c32" + + will still work, but are now deprecated. - reg : the I2C address of the EEPROM