| Message ID | 20220804175746.3746-1-msuchanek@suse.de |
|---|---|
| State | Accepted, archived |
| Delegated to: | Heinrich Schuchardt |
| Headers | show |
| Series | doc: dm: clarify activation. | expand |
Hi Michal, On Thu, 4 Aug 2022 at 11:58, Michal Suchanek <msuchanek@suse.de> wrote: > > Explain when devices should get activated. > > Signed-off-by: Michal Suchanek <msuchanek@suse.de> > --- > doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- > 1 file changed, 20 insertions(+), 2 deletions(-) Reviewed-by: Simon Glass <sjg@chromium.org> Much appreciated! one note below > > diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst > index 5f33f9fbb3..c925d21b24 100644 > --- a/doc/develop/driver-model/design.rst > +++ b/doc/develop/driver-model/design.rst > @@ -794,8 +794,26 @@ fall afoul of this rule. > Activation/probe > ^^^^^^^^^^^^^^^^ > > -When a device needs to be used, U-Boot activates it, by first reading ofdata > -as above and then following these steps (see device_probe()): > +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, > +not an operating system. Many devices are never used during an U-Boot run, and > +probing them takes time, requires memory, may add delays to the main loop, etc. > + > +The device should be probed by the uclass code. Different uclasses are or the device code (e.g. device_get_child()) BTW probing a child probes all its parents automatically (that is said elsewhere I think). > +different but two common use cases can be seen: > + > + 1. The uclass is asked to look up a specific device, such as SPI bus 0, > + first chip select - in this case the returned device should be > + activated. > + > + 2. The uclass is asked to perform a specific function on any device that > + supports it, eg. reset the board using any sysreset that can be found - > + for this case the core uclass code provides iterators that activate > + each device before returning it, and the uclass typically implements a > + walk function that iterates over all devices of the uclass and tries > + to perform the requested function on each in turn until succesful. > + > +To activate a device U-Boot first reads ofdata as above and then follows these > +steps (see device_probe()): > > 1. All parent devices are probed. It is not possible to activate a device > unless its predecessors (all the way up to the root device) are activated. > -- > 2.37.1 > Regards, Simon
On Thu, Aug 04, 2022 at 01:22:53PM -0600, Simon Glass wrote: > Hi Michal, > > On Thu, 4 Aug 2022 at 11:58, Michal Suchanek <msuchanek@suse.de> wrote: > > > > Explain when devices should get activated. > > > > Signed-off-by: Michal Suchanek <msuchanek@suse.de> > > --- > > doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- > > 1 file changed, 20 insertions(+), 2 deletions(-) > > Reviewed-by: Simon Glass <sjg@chromium.org> > > Much appreciated! > > one note below > > > > > diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst > > index 5f33f9fbb3..c925d21b24 100644 > > --- a/doc/develop/driver-model/design.rst > > +++ b/doc/develop/driver-model/design.rst > > @@ -794,8 +794,26 @@ fall afoul of this rule. > > Activation/probe > > ^^^^^^^^^^^^^^^^ > > > > -When a device needs to be used, U-Boot activates it, by first reading ofdata > > -as above and then following these steps (see device_probe()): > > +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, > > +not an operating system. Many devices are never used during an U-Boot run, and > > +probing them takes time, requires memory, may add delays to the main loop, etc. > > + > > +The device should be probed by the uclass code. Different uclasses are > > or the device code (e.g. device_get_child()) Can you elaborate a bit more, please? This change is the reasult of some previous discussion about the device activation with Marek. The device activation is really difficult to understand for people who did not participate in designing the DM, and is probably quite specific to U-Boot. > > BTW probing a child probes all its parents automatically (that is said > elsewhere I think). Yes, right below this part. Thanks Michal > > > +different but two common use cases can be seen: > > + > > + 1. The uclass is asked to look up a specific device, such as SPI bus 0, > > + first chip select - in this case the returned device should be > > + activated. > > + > > + 2. The uclass is asked to perform a specific function on any device that > > + supports it, eg. reset the board using any sysreset that can be found - > > + for this case the core uclass code provides iterators that activate > > + each device before returning it, and the uclass typically implements a > > + walk function that iterates over all devices of the uclass and tries > > + to perform the requested function on each in turn until succesful. > > + > > +To activate a device U-Boot first reads ofdata as above and then follows these > > +steps (see device_probe()): > > > > 1. All parent devices are probed. It is not possible to activate a device > > unless its predecessors (all the way up to the root device) are activated. > > -- > > 2.37.1 > > > > Regards, > Simon
Hi Michal, On Thu, 4 Aug 2022 at 13:42, Michal Suchánek <msuchanek@suse.de> wrote: > > On Thu, Aug 04, 2022 at 01:22:53PM -0600, Simon Glass wrote: > > Hi Michal, > > > > On Thu, 4 Aug 2022 at 11:58, Michal Suchanek <msuchanek@suse.de> wrote: > > > > > > Explain when devices should get activated. > > > > > > Signed-off-by: Michal Suchanek <msuchanek@suse.de> > > > --- > > > doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- > > > 1 file changed, 20 insertions(+), 2 deletions(-) > > > > Reviewed-by: Simon Glass <sjg@chromium.org> > > > > Much appreciated! > > > > one note below > > > > > > > > diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst > > > index 5f33f9fbb3..c925d21b24 100644 > > > --- a/doc/develop/driver-model/design.rst > > > +++ b/doc/develop/driver-model/design.rst > > > @@ -794,8 +794,26 @@ fall afoul of this rule. > > > Activation/probe > > > ^^^^^^^^^^^^^^^^ > > > > > > -When a device needs to be used, U-Boot activates it, by first reading ofdata > > > -as above and then following these steps (see device_probe()): > > > +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, > > > +not an operating system. Many devices are never used during an U-Boot run, and > > > +probing them takes time, requires memory, may add delays to the main loop, etc. > > > + > > > +The device should be probed by the uclass code. Different uclasses are > > > > or the device code (e.g. device_get_child()) > > Can you elaborate a bit more, please? I mean that we can use 'device' code to probe, as well as the 'uclass' code. The function I cite is an example of that, but actually a better one is device_find_global_by_ofnode() > > This change is the reasult of some previous discussion about the device > activation with Marek. > > The device activation is really difficult to understand for people who > did not participate in designing the DM, and is probably quite specific > to U-Boot. OK, well good to have it. I wish more people would do what you have done here, i.e. go back and update the docs to clarify things that you found confusing / inadequate. > > > > > BTW probing a child probes all its parents automatically (that is said > > elsewhere I think). > > Yes, right below this part. > > Thanks > > Michal OK Regards, Simon > > > > > > +different but two common use cases can be seen: > > > + > > > + 1. The uclass is asked to look up a specific device, such as SPI bus 0, > > > + first chip select - in this case the returned device should be > > > + activated. > > > + > > > + 2. The uclass is asked to perform a specific function on any device that > > > + supports it, eg. reset the board using any sysreset that can be found - > > > + for this case the core uclass code provides iterators that activate > > > + each device before returning it, and the uclass typically implements a > > > + walk function that iterates over all devices of the uclass and tries > > > + to perform the requested function on each in turn until succesful. > > > + > > > +To activate a device U-Boot first reads ofdata as above and then follows these > > > +steps (see device_probe()): > > > > > > 1. All parent devices are probed. It is not possible to activate a device > > > unless its predecessors (all the way up to the root device) are activated. > > > -- > > > 2.37.1 > > > > > > > Regards, > > Simon
On 8/4/22 22:30, Simon Glass wrote: > Hi Michal, > > On Thu, 4 Aug 2022 at 13:42, Michal Suchánek <msuchanek@suse.de> wrote: >> >> On Thu, Aug 04, 2022 at 01:22:53PM -0600, Simon Glass wrote: >>> Hi Michal, >>> >>> On Thu, 4 Aug 2022 at 11:58, Michal Suchanek <msuchanek@suse.de> wrote: >>>> >>>> Explain when devices should get activated. >>>> >>>> Signed-off-by: Michal Suchanek <msuchanek@suse.de> >>>> --- >>>> doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- >>>> 1 file changed, 20 insertions(+), 2 deletions(-) >>> >>> Reviewed-by: Simon Glass <sjg@chromium.org> >>> >>> Much appreciated! >>> >>> one note below >>> >>>> >>>> diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst >>>> index 5f33f9fbb3..c925d21b24 100644 >>>> --- a/doc/develop/driver-model/design.rst >>>> +++ b/doc/develop/driver-model/design.rst >>>> @@ -794,8 +794,26 @@ fall afoul of this rule. >>>> Activation/probe >>>> ^^^^^^^^^^^^^^^^ >>>> >>>> -When a device needs to be used, U-Boot activates it, by first reading ofdata >>>> -as above and then following these steps (see device_probe()): >>>> +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, >>>> +not an operating system. Many devices are never used during an U-Boot run, and >>>> +probing them takes time, requires memory, may add delays to the main loop, etc. >>>> + >>>> +The device should be probed by the uclass code. Different uclasses are When merging I will put the following here: The device should be probed by the uclass code or generic device code (e.g. device_find_global_by_ofnode()). Uclasses differ but two common use cases can be seen: Best regards Heinrich >>> >>> or the device code (e.g. device_get_child()) >> >> Can you elaborate a bit more, please? > > I mean that we can use 'device' code to probe, as well as the 'uclass' > code. The function I cite is an example of that, but actually a better > one is device_find_global_by_ofnode() > >> >> This change is the reasult of some previous discussion about the device >> activation with Marek. >> >> The device activation is really difficult to understand for people who >> did not participate in designing the DM, and is probably quite specific >> to U-Boot. > > OK, well good to have it. I wish more people would do what you have > done here, i.e. go back and update the docs to clarify things that you > found confusing / inadequate. > >> >>> >>> BTW probing a child probes all its parents automatically (that is said >>> elsewhere I think). >> >> Yes, right below this part. >> >> Thanks >> >> Michal > > OK > > Regards, > Simon > > >> >>> >>>> +different but two common use cases can be seen: >>>> + >>>> + 1. The uclass is asked to look up a specific device, such as SPI bus 0, >>>> + first chip select - in this case the returned device should be >>>> + activated. >>>> + >>>> + 2. The uclass is asked to perform a specific function on any device that >>>> + supports it, eg. reset the board using any sysreset that can be found - >>>> + for this case the core uclass code provides iterators that activate >>>> + each device before returning it, and the uclass typically implements a >>>> + walk function that iterates over all devices of the uclass and tries >>>> + to perform the requested function on each in turn until succesful. >>>> + >>>> +To activate a device U-Boot first reads ofdata as above and then follows these >>>> +steps (see device_probe()): >>>> >>>> 1. All parent devices are probed. It is not possible to activate a device >>>> unless its predecessors (all the way up to the root device) are activated. >>>> -- >>>> 2.37.1 >>>> >>> >>> Regards, >>> Simon
Hello, On Sat, Aug 20, 2022 at 08:27:05AM +0200, Heinrich Schuchardt wrote: > On 8/4/22 22:30, Simon Glass wrote: > > Hi Michal, > > > > On Thu, 4 Aug 2022 at 13:42, Michal Suchánek <msuchanek@suse.de> wrote: > > > > > > On Thu, Aug 04, 2022 at 01:22:53PM -0600, Simon Glass wrote: > > > > Hi Michal, > > > > > > > > On Thu, 4 Aug 2022 at 11:58, Michal Suchanek <msuchanek@suse.de> wrote: > > > > > > > > > > Explain when devices should get activated. > > > > > > > > > > Signed-off-by: Michal Suchanek <msuchanek@suse.de> > > > > > --- > > > > > doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- > > > > > 1 file changed, 20 insertions(+), 2 deletions(-) > > > > > > > > Reviewed-by: Simon Glass <sjg@chromium.org> > > > > > > > > Much appreciated! > > > > > > > > one note below > > > > > > > > > > > > > > diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst > > > > > index 5f33f9fbb3..c925d21b24 100644 > > > > > --- a/doc/develop/driver-model/design.rst > > > > > +++ b/doc/develop/driver-model/design.rst > > > > > @@ -794,8 +794,26 @@ fall afoul of this rule. > > > > > Activation/probe > > > > > ^^^^^^^^^^^^^^^^ > > > > > > > > > > -When a device needs to be used, U-Boot activates it, by first reading ofdata > > > > > -as above and then following these steps (see device_probe()): > > > > > +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, > > > > > +not an operating system. Many devices are never used during an U-Boot run, and > > > > > +probing them takes time, requires memory, may add delays to the main loop, etc. > > > > > + > > > > > +The device should be probed by the uclass code. Different uclasses are > > When merging I will put the following here: > > The device should be probed by the uclass code or generic device code > (e.g. device_find_global_by_ofnode()). Uclasses differ but two common > use cases can be seen: I wanted to look at this direct device lookup, and send a v2 when I am done with it. I am currently trying to figure out how (if at all) the pins and clocks required by i2c devices are activated, and I suppose this direct lookup would be related. Noneteless, if you can fix up the patch right away that's great. Thanks Michal > > Best regards > > Heinrich > > > > > > > > > or the device code (e.g. device_get_child()) > > > > > > Can you elaborate a bit more, please? > > > > I mean that we can use 'device' code to probe, as well as the 'uclass' > > code. The function I cite is an example of that, but actually a better > > one is device_find_global_by_ofnode() > > > > > > > > This change is the reasult of some previous discussion about the device > > > activation with Marek. > > > > > > The device activation is really difficult to understand for people who > > > did not participate in designing the DM, and is probably quite specific > > > to U-Boot. > > > > OK, well good to have it. I wish more people would do what you have > > done here, i.e. go back and update the docs to clarify things that you > > found confusing / inadequate. > > > > > > > > > > > > > BTW probing a child probes all its parents automatically (that is said > > > > elsewhere I think). > > > > > > Yes, right below this part. > > > > > > Thanks > > > > > > Michal > > > > OK > > > > Regards, > > Simon > > > > > > > > > > > > > > > > +different but two common use cases can be seen: > > > > > + > > > > > + 1. The uclass is asked to look up a specific device, such as SPI bus 0, > > > > > + first chip select - in this case the returned device should be > > > > > + activated. > > > > > + > > > > > + 2. The uclass is asked to perform a specific function on any device that > > > > > + supports it, eg. reset the board using any sysreset that can be found - > > > > > + for this case the core uclass code provides iterators that activate > > > > > + each device before returning it, and the uclass typically implements a > > > > > + walk function that iterates over all devices of the uclass and tries > > > > > + to perform the requested function on each in turn until succesful. > > > > > + > > > > > +To activate a device U-Boot first reads ofdata as above and then follows these > > > > > +steps (see device_probe()): > > > > > > > > > > 1. All parent devices are probed. It is not possible to activate a device > > > > > unless its predecessors (all the way up to the root device) are activated. > > > > > -- > > > > > 2.37.1 > > > > > > > > > > > > > Regards, > > > > Simon >
diff --git a/doc/develop/driver-model/design.rst b/doc/develop/driver-model/design.rst index 5f33f9fbb3..c925d21b24 100644 --- a/doc/develop/driver-model/design.rst +++ b/doc/develop/driver-model/design.rst @@ -794,8 +794,26 @@ fall afoul of this rule. Activation/probe ^^^^^^^^^^^^^^^^ -When a device needs to be used, U-Boot activates it, by first reading ofdata -as above and then following these steps (see device_probe()): +To save resources devices in U-Boot are probed lazily. U-Boot is a bootloader, +not an operating system. Many devices are never used during an U-Boot run, and +probing them takes time, requires memory, may add delays to the main loop, etc. + +The device should be probed by the uclass code. Different uclasses are +different but two common use cases can be seen: + + 1. The uclass is asked to look up a specific device, such as SPI bus 0, + first chip select - in this case the returned device should be + activated. + + 2. The uclass is asked to perform a specific function on any device that + supports it, eg. reset the board using any sysreset that can be found - + for this case the core uclass code provides iterators that activate + each device before returning it, and the uclass typically implements a + walk function that iterates over all devices of the uclass and tries + to perform the requested function on each in turn until succesful. + +To activate a device U-Boot first reads ofdata as above and then follows these +steps (see device_probe()): 1. All parent devices are probed. It is not possible to activate a device unless its predecessors (all the way up to the root device) are activated.
Explain when devices should get activated. Signed-off-by: Michal Suchanek <msuchanek@suse.de> --- doc/develop/driver-model/design.rst | 22 ++++++++++++++++++++-- 1 file changed, 20 insertions(+), 2 deletions(-)