| Message ID | 20200619141904.910889-2-codrin.ciubotariu@microchip.com |
|---|---|
| State | Superseded |
| Headers | show |
| Series | i2c: core: add generic GPIO bus recovery | expand |
> +- pinctrl > + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > + recovery, call it "gpio" or "recovery" state I think we should stick with "gpio" only. That is what at91 and imx have in their bindings. pxa uses "recovery" as a pinctrl state name but I can't find any further use or documentation of that. PXA is not fully converted to the best of my knowledge, so maybe it is no problem for PXA to switch to "gpio", too? We should ask Russell King (cced). Russell, do you object naming the pinctrl state for bus recovery in the pxa i2c driver from "recovery" to "gpio"?
On Fri, 19 Jun 2020 17:19:01 +0300, Codrin Ciubotariu wrote: > The I2C GPIO bus recovery properties consist of two GPIOS and one extra > pinctrl state ("gpio" or "recovery"). Not all are mandatory for recovery. > > Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com> > --- > Documentation/devicetree/bindings/i2c/i2c.txt | 10 ++++++++++ > 1 file changed, 10 insertions(+) > Reviewed-by: Rob Herring <robh@kernel.org>
On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: > > > +- pinctrl > > + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > > + recovery, call it "gpio" or "recovery" state > > I think we should stick with "gpio" only. That is what at91 and imx have > in their bindings. pxa uses "recovery" as a pinctrl state name but I > can't find any further use or documentation of that. PXA is not fully > converted to the best of my knowledge, so maybe it is no problem for PXA > to switch to "gpio", too? We should ask Russell King (cced). > > Russell, do you object naming the pinctrl state for bus recovery in > the pxa i2c driver from "recovery" to "gpio"? No response, so far. I suggest now to support the "recovery" naming but mark it as deprecated. Opinions?
On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: > On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: > > > > > +- pinctrl > > > + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > > > + recovery, call it "gpio" or "recovery" state > > > > I think we should stick with "gpio" only. That is what at91 and imx have > > in their bindings. pxa uses "recovery" as a pinctrl state name but I > > can't find any further use or documentation of that. PXA is not fully > > converted to the best of my knowledge, so maybe it is no problem for PXA > > to switch to "gpio", too? We should ask Russell King (cced). Fully converted to what? The generic handling where the i2c core layer handles everything to do with recovery, including the switch between modes? i2c-pxa _intentionally_ carefully handles the switch between i2c mode and GPIO mode, and I don't see a generic driver doing that to avoid causing any additional glitches on the bus. Given the use case that this recovery is targetted at, avoiding glitches is very important to keep. > > Russell, do you object naming the pinctrl state for bus recovery in > > the pxa i2c driver from "recovery" to "gpio"? > > No response, so far. I suggest now to support the "recovery" naming but > mark it as deprecated. Opinions? I don't have a preference on the exact naming.
On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: >> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: >>> >>>> +- pinctrl >>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus >>>> + recovery, call it "gpio" or "recovery" state >>> >>> I think we should stick with "gpio" only. That is what at91 and imx have >>> in their bindings. pxa uses "recovery" as a pinctrl state name but I >>> can't find any further use or documentation of that. PXA is not fully >>> converted to the best of my knowledge, so maybe it is no problem for PXA >>> to switch to "gpio", too? We should ask Russell King (cced). > > Fully converted to what? The generic handling where the i2c core layer > handles everything to do with recovery, including the switch between > modes? > > i2c-pxa _intentionally_ carefully handles the switch between i2c mode and > GPIO mode, and I don't see a generic driver doing that to avoid causing > any additional glitches on the bus. Given the use case that this recovery > is targetted at, avoiding glitches is very important to keep. Why is it not possbile to handle glitches in a generic way? I guess it depends on the pinctl, but we could treat a worst-case scenario to assure the switch between states is done properly. > >>> Russell, do you object naming the pinctrl state for bus recovery in >>> the pxa i2c driver from "recovery" to "gpio"? >> >> No response, so far. I suggest now to support the "recovery" naming but >> mark it as deprecated. Opinions? > > I don't have a preference on the exact naming. > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! >
On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote: > On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > > > On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: > >> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: > >>> > >>>> +- pinctrl > >>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > >>>> + recovery, call it "gpio" or "recovery" state > >>> > >>> I think we should stick with "gpio" only. That is what at91 and imx have > >>> in their bindings. pxa uses "recovery" as a pinctrl state name but I > >>> can't find any further use or documentation of that. PXA is not fully > >>> converted to the best of my knowledge, so maybe it is no problem for PXA > >>> to switch to "gpio", too? We should ask Russell King (cced). > > > > Fully converted to what? The generic handling where the i2c core layer > > handles everything to do with recovery, including the switch between > > modes? > > > > i2c-pxa _intentionally_ carefully handles the switch between i2c mode and > > GPIO mode, and I don't see a generic driver doing that to avoid causing > > any additional glitches on the bus. Given the use case that this recovery > > is targetted at, avoiding glitches is very important to keep. > > Why is it not possbile to handle glitches in a generic way? I guess it > depends on the pinctl, but we could treat a worst-case scenario to > assure the switch between states is done properly. Please look at how i2c-pxa switches between the two, and decide whether the generic implementation can do the same.
On 27.07.2020 13:50, Russell King - ARM Linux admin wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote: >> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe >>> >>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: >>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: >>>>> >>>>>> +- pinctrl >>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus >>>>>> + recovery, call it "gpio" or "recovery" state >>>>> >>>>> I think we should stick with "gpio" only. That is what at91 and imx have >>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I >>>>> can't find any further use or documentation of that. PXA is not fully >>>>> converted to the best of my knowledge, so maybe it is no problem for PXA >>>>> to switch to "gpio", too? We should ask Russell King (cced). >>> >>> Fully converted to what? The generic handling where the i2c core layer >>> handles everything to do with recovery, including the switch between >>> modes? >>> >>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and >>> GPIO mode, and I don't see a generic driver doing that to avoid causing >>> any additional glitches on the bus. Given the use case that this recovery >>> is targetted at, avoiding glitches is very important to keep. >> >> Why is it not possbile to handle glitches in a generic way? I guess it >> depends on the pinctl, but we could treat a worst-case scenario to >> assure the switch between states is done properly. > > Please look at how i2c-pxa switches between the two, and decide whether > the generic implementation can do the same. The handling of glitches from initialization looks generic to me. I see that there are specific clear/reset routines that are in the (un)prepare_recovery() callbacks, but these callbacks are not replaced by the generic i2c recovery and will still be used if given by the driver. The only thing the generic recovery does is to switch the pinmux state. We can discuss whether we want to change the pinmux state first or call the (un)preapre_recovery(). What I had in mind for the generic recovery was to just handle the common parts that follow the same bindings, which is getting the gpios and changing the pinmux states before recovering. Best regards, Codrin > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! >
On Thu, Jul 30, 2020 at 09:00:36AM +0000, Codrin.Ciubotariu@microchip.com wrote: > On 27.07.2020 13:50, Russell King - ARM Linux admin wrote: > > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > > > On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote: > >> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: > >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > >>> > >>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: > >>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: > >>>>> > >>>>>> +- pinctrl > >>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus > >>>>>> + recovery, call it "gpio" or "recovery" state > >>>>> > >>>>> I think we should stick with "gpio" only. That is what at91 and imx have > >>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I > >>>>> can't find any further use or documentation of that. PXA is not fully > >>>>> converted to the best of my knowledge, so maybe it is no problem for PXA > >>>>> to switch to "gpio", too? We should ask Russell King (cced). > >>> > >>> Fully converted to what? The generic handling where the i2c core layer > >>> handles everything to do with recovery, including the switch between > >>> modes? > >>> > >>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and > >>> GPIO mode, and I don't see a generic driver doing that to avoid causing > >>> any additional glitches on the bus. Given the use case that this recovery > >>> is targetted at, avoiding glitches is very important to keep. > >> > >> Why is it not possbile to handle glitches in a generic way? I guess it > >> depends on the pinctl, but we could treat a worst-case scenario to > >> assure the switch between states is done properly. > > > > Please look at how i2c-pxa switches between the two, and decide whether > > the generic implementation can do the same. > > The handling of glitches from initialization looks generic to me. I see > that there are specific clear/reset routines that are in the > (un)prepare_recovery() callbacks, but these callbacks are not replaced > by the generic i2c recovery and will still be used if given by the > driver. The only thing the generic recovery does is to switch the pinmux > state. We can discuss whether we want to change the pinmux state first > or call the (un)preapre_recovery(). Right, the key point i2c-pxa does is that on prepare: - read the current state of the SCL and SDA lines and set the GPIO to reflect those values. - then switch the pinmux state. That must be preserved, otherwise if SCL is being held low by the I2C master, and we switch to GPIO mode, SCL will be released. So the driver needs to be involved before the pinmux state is changed.
On 03.08.2020 17:16, Russell King - ARM Linux admin wrote: > EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe > > On Thu, Jul 30, 2020 at 09:00:36AM +0000, Codrin.Ciubotariu@microchip.com wrote: >> On 27.07.2020 13:50, Russell King - ARM Linux admin wrote: >>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe >>> >>> On Mon, Jul 27, 2020 at 10:44:57AM +0000, Codrin.Ciubotariu@microchip.com wrote: >>>> On 24.07.2020 23:52, Russell King - ARM Linux admin wrote: >>>>> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe >>>>> >>>>> On Fri, Jul 24, 2020 at 09:39:13PM +0200, Wolfram Sang wrote: >>>>>> On Sun, Jul 05, 2020 at 11:19:18PM +0200, Wolfram Sang wrote: >>>>>>> >>>>>>>> +- pinctrl >>>>>>>> + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus >>>>>>>> + recovery, call it "gpio" or "recovery" state >>>>>>> >>>>>>> I think we should stick with "gpio" only. That is what at91 and imx have >>>>>>> in their bindings. pxa uses "recovery" as a pinctrl state name but I >>>>>>> can't find any further use or documentation of that. PXA is not fully >>>>>>> converted to the best of my knowledge, so maybe it is no problem for PXA >>>>>>> to switch to "gpio", too? We should ask Russell King (cced). >>>>> >>>>> Fully converted to what? The generic handling where the i2c core layer >>>>> handles everything to do with recovery, including the switch between >>>>> modes? >>>>> >>>>> i2c-pxa _intentionally_ carefully handles the switch between i2c mode and >>>>> GPIO mode, and I don't see a generic driver doing that to avoid causing >>>>> any additional glitches on the bus. Given the use case that this recovery >>>>> is targetted at, avoiding glitches is very important to keep. >>>> >>>> Why is it not possbile to handle glitches in a generic way? I guess it >>>> depends on the pinctl, but we could treat a worst-case scenario to >>>> assure the switch between states is done properly. >>> >>> Please look at how i2c-pxa switches between the two, and decide whether >>> the generic implementation can do the same. >> >> The handling of glitches from initialization looks generic to me. I see >> that there are specific clear/reset routines that are in the >> (un)prepare_recovery() callbacks, but these callbacks are not replaced >> by the generic i2c recovery and will still be used if given by the >> driver. The only thing the generic recovery does is to switch the pinmux >> state. We can discuss whether we want to change the pinmux state first >> or call the (un)preapre_recovery(). > > Right, the key point i2c-pxa does is that on prepare: > - read the current state of the SCL and SDA lines and set the GPIO to > reflect those values. > - then switch the pinmux state. > > That must be preserved, otherwise if SCL is being held low by the I2C > master, and we switch to GPIO mode, SCL will be released. So the > driver needs to be involved before the pinmux state is changed. I understand, and I admit that I didn't see this case. In my mind, the master would always be in (almost) a reset state before calling for SDA recovery, so it won't hold any lines. These steps can't be generic, of course. Also, not all I2C masters have a way to show the state of its lines. For these masters, one idea would be to reset them before calling i2c_recover_bus() > > -- > RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ > FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last! >
diff --git a/Documentation/devicetree/bindings/i2c/i2c.txt b/Documentation/devicetree/bindings/i2c/i2c.txt index 438ae123107e..6a644a24fc1c 100644 --- a/Documentation/devicetree/bindings/i2c/i2c.txt +++ b/Documentation/devicetree/bindings/i2c/i2c.txt @@ -77,6 +77,16 @@ wants to support one of the below features, it should adapt these bindings. this information to detect a stalled bus more reliably, for example. Can not be combined with 'multi-master'. +- scl-gpios + specify the gpio related to SCL pin. Used for GPIO bus recovery. + +- sda-gpios + specify the gpio related to SDA pin. Optional for GPIO bus recovery. + +- pinctrl + add extra pinctrl to configure SCL/SDA pins to GPIO function for bus + recovery, call it "gpio" or "recovery" state + Required properties (per child device) --------------------------------------
The I2C GPIO bus recovery properties consist of two GPIOS and one extra pinctrl state ("gpio" or "recovery"). Not all are mandatory for recovery. Signed-off-by: Codrin Ciubotariu <codrin.ciubotariu@microchip.com> --- Documentation/devicetree/bindings/i2c/i2c.txt | 10 ++++++++++ 1 file changed, 10 insertions(+)