[v3,20/20] dt-bindings: pwm: sti: Update DT bindings with recent changes

Message ID 20160608092135.21184-21-lee.jones@linaro.org
State New
Headers show

Commit Message

Lee Jones June 8, 2016, 9:21 a.m.
We're renaming the 'st,pwm-num-chan' binding to 'st,pwm-num-devs' to
be more inline with the naming conventions of the subsystem.  Where
we used to treat each line as a channel, the PWM convention is to
describe them as devices.

The second documentation adaption entails adding support for PWM
capture devices.  A new clock is required as well as an IRQ line.
We're also adding a new property similar to the one described
above, but for capture channels.  Typically, there will be less
capture channels than PWM-out, since all channels have the latter
capability, but only some have capture support.

Signed-off-by: Lee Jones <lee.jones@linaro.org>

---
 Documentation/devicetree/bindings/pwm/pwm-st.txt | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

-- 
2.8.3

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Comments

Rob Herring June 8, 2016, 8:51 p.m. | #1
On Wed, Jun 08, 2016 at 10:21:35AM +0100, Lee Jones wrote:
> We're renaming the 'st,pwm-num-chan' binding to 'st,pwm-num-devs' to

> be more inline with the naming conventions of the subsystem.  Where

> we used to treat each line as a channel, the PWM convention is to

> describe them as devices.


That's all linux implementation details and you are breaking 
compatibility.

> The second documentation adaption entails adding support for PWM

> capture devices.  A new clock is required as well as an IRQ line.

> We're also adding a new property similar to the one described

> above, but for capture channels.  Typically, there will be less

> capture channels than PWM-out, since all channels have the latter

> capability, but only some have capture support.


Humm, sounds like all of this should be implied from compatible strings.

> 

> Signed-off-by: Lee Jones <lee.jones@linaro.org>

> ---

>  Documentation/devicetree/bindings/pwm/pwm-st.txt | 10 ++++++----

>  1 file changed, 6 insertions(+), 4 deletions(-)

> 

> diff --git a/Documentation/devicetree/bindings/pwm/pwm-st.txt b/Documentation/devicetree/bindings/pwm/pwm-st.txt

> index 84d2fb8..b09f3a4 100644

> --- a/Documentation/devicetree/bindings/pwm/pwm-st.txt

> +++ b/Documentation/devicetree/bindings/pwm/pwm-st.txt

> @@ -13,13 +13,14 @@ Required parameters:

>  - pinctrl-0: 		List of phandles pointing to pin configuration nodes

>  			for PWM module.

>  			For Pinctrl properties, please refer to [1].

> -- clock-names: 		Set to "pwm".

> +- clock-names: 		Valid entries are "pwm" and/or "capture".

>  - clocks: 		phandle of the clock used by the PWM module.

>  			For Clk properties, please refer to [2].

> +- interrupts:		IRQ for the Capture device

>  

>  Optional properties:

> -- st,pwm-num-chan:	Number of available channels. If not passed, the driver

> -			will consider single channel by default.

> +- st,pwm-num-devs:	Number of available PWM channels.  Default is 0.

> +- st,capture-num-devs:	Number of available Capture channels.  Default is 0.

>  

>  [1] Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

>  [2] Documentation/devicetree/bindings/clock/clock-bindings.txt

> @@ -37,5 +38,6 @@ pwm1: pwm@fe510000 {

>  		     &pinctrl_pwm1_chan3_default>;

>  	clocks = <&clk_sysin>;

>  	clock-names = "pwm";

> -	st,pwm-num-chan = <4>;

> +	st,pwm-num-devs = <4>;

> +	st,capture-num-devs = <2>;

>  };

> -- 

> 2.8.3

> 

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Lee Jones June 9, 2016, 11:41 a.m. | #2
On Wed, 08 Jun 2016, Rob Herring wrote:

> On Wed, Jun 08, 2016 at 10:21:35AM +0100, Lee Jones wrote:

> > We're renaming the 'st,pwm-num-chan' binding to 'st,pwm-num-devs' to

> > be more inline with the naming conventions of the subsystem.  Where

> > we used to treat each line as a channel, the PWM convention is to

> > describe them as devices.

> 

> That's all linux implementation details and you are breaking 

> compatibility.


Normally I'd agree with you, but I happen to know that a) this IP is
currently unused and b) up until this point (and probably beyond), ST
always ship the DTB with the kernel, so there will be no breakage.

> > The second documentation adaption entails adding support for PWM

> > capture devices.  A new clock is required as well as an IRQ line.

> > We're also adding a new property similar to the one described

> > above, but for capture channels.  Typically, there will be less

> > capture channels than PWM-out, since all channels have the latter

> > capability, but only some have capture support.

> 

> Humm, sounds like all of this should be implied from compatible strings.


You mean have a bunch of of_machine_is_compatibles() scattered around?

> > Signed-off-by: Lee Jones <lee.jones@linaro.org>

> > ---

> >  Documentation/devicetree/bindings/pwm/pwm-st.txt | 10 ++++++----

> >  1 file changed, 6 insertions(+), 4 deletions(-)

> > 

> > diff --git a/Documentation/devicetree/bindings/pwm/pwm-st.txt b/Documentation/devicetree/bindings/pwm/pwm-st.txt

> > index 84d2fb8..b09f3a4 100644

> > --- a/Documentation/devicetree/bindings/pwm/pwm-st.txt

> > +++ b/Documentation/devicetree/bindings/pwm/pwm-st.txt

> > @@ -13,13 +13,14 @@ Required parameters:

> >  - pinctrl-0: 		List of phandles pointing to pin configuration nodes

> >  			for PWM module.

> >  			For Pinctrl properties, please refer to [1].

> > -- clock-names: 		Set to "pwm".

> > +- clock-names: 		Valid entries are "pwm" and/or "capture".

> >  - clocks: 		phandle of the clock used by the PWM module.

> >  			For Clk properties, please refer to [2].

> > +- interrupts:		IRQ for the Capture device

> >  

> >  Optional properties:

> > -- st,pwm-num-chan:	Number of available channels. If not passed, the driver

> > -			will consider single channel by default.

> > +- st,pwm-num-devs:	Number of available PWM channels.  Default is 0.

> > +- st,capture-num-devs:	Number of available Capture channels.  Default is 0.

> >  

> >  [1] Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt

> >  [2] Documentation/devicetree/bindings/clock/clock-bindings.txt

> > @@ -37,5 +38,6 @@ pwm1: pwm@fe510000 {

> >  		     &pinctrl_pwm1_chan3_default>;

> >  	clocks = <&clk_sysin>;

> >  	clock-names = "pwm";

> > -	st,pwm-num-chan = <4>;

> > +	st,pwm-num-devs = <4>;

> > +	st,capture-num-devs = <2>;

> >  };


-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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Lee Jones June 10, 2016, 2:06 p.m. | #3
On Fri, 10 Jun 2016, Thierry Reding wrote:

> On Thu, Jun 09, 2016 at 12:41:07PM +0100, Lee Jones wrote:

> > On Wed, 08 Jun 2016, Rob Herring wrote:

> > 

> > > On Wed, Jun 08, 2016 at 10:21:35AM +0100, Lee Jones wrote:

> > > > We're renaming the 'st,pwm-num-chan' binding to 'st,pwm-num-devs' to

> > > > be more inline with the naming conventions of the subsystem.  Where

> > > > we used to treat each line as a channel, the PWM convention is to

> > > > describe them as devices.

> > > 

> > > That's all linux implementation details and you are breaking 

> > > compatibility.

> > 

> > Normally I'd agree with you, but I happen to know that a) this IP is

> > currently unused and b) up until this point (and probably beyond), ST

> > always ship the DTB with the kernel, so there will be no breakage.

> 

> Heh... I've long given up on trying to make that argument go anywhere.

> The general rule is that once we support a binding in a kernel release

> we have to support it indefinitely. If you really want to go ahead with

> this change (I don't think you should), you'd at least have to document

> both properties and support st,pwm-num-chan in the driver for backwards

> compatibility.


I understand what the *general* rule is, but we have to remember why
this rule was put into place and apply some common sense.  In some
Enterprise user-cases where DTBs are written into ROM or where they
are difficult /impossible to update, I can completely understand the
requirement to support previous incarnations.  However in this, the
real world, DTBs are shipped with their corresponding kernels.  We
would lack a great deal of functionality if they weren't.  It is
therefor, foolhardy and inappropriate to stick to this rule just
'cos.

> > > > The second documentation adaption entails adding support for PWM

> > > > capture devices.  A new clock is required as well as an IRQ line.

> > > > We're also adding a new property similar to the one described

> > > > above, but for capture channels.  Typically, there will be less

> > > > capture channels than PWM-out, since all channels have the latter

> > > > capability, but only some have capture support.

> > > 

> > > Humm, sounds like all of this should be implied from compatible strings.

> > 

> > You mean have a bunch of of_machine_is_compatibles() scattered around?

> 

> I don't understand why you need this at all. Quite frankly I don't even

> know why st,pwm-num-devs exists. I probably missed it back at the time.

> Usually, like Rob suggests, this should be inferred from the compatible

> string. One commonly used way to avoid scattering explicit checks for

> the compatible string is to add this information to the of_device_id

> table. See a bunch of existing drivers for reference.


Yes, I am aware of the strategy, and happy to oblige if this is your
suggestion.  I'll move all platform data into the driver and eradicate
the DT properties.

> Also, why make a separation of output vs. capture channels at this

> point? Could you not simply obtain the total number of PWM channels,

> preferably from SoC data associated with the compatible string, and

> check at ->capture() time whether or not the particular PWM supports

> this?

> 

> As-is, you imply that you have n (output) + m (capture) channels, and

> that 0..n-1 are output and n..n+m-1 are capture channels. What if that

> no longer holds true, but 0 and 2 are the only ones that support

> capture?


We do?  What makes you think that?

> If you check for this at runtime you can avoid complicated DT parsing

> code, but still get the safety check which should be enough to encourage

> people to use the right channels in DT.


I'm pretty sure I can move all the data into the driver.  I did want
to avoid having lots of different compatible strings, but if that's
what you're suggesting, I can introduce one per supported platform.

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
Follow Linaro: Facebook | Twitter | Blog
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Patch

diff --git a/Documentation/devicetree/bindings/pwm/pwm-st.txt b/Documentation/devicetree/bindings/pwm/pwm-st.txt
index 84d2fb8..b09f3a4 100644
--- a/Documentation/devicetree/bindings/pwm/pwm-st.txt
+++ b/Documentation/devicetree/bindings/pwm/pwm-st.txt
@@ -13,13 +13,14 @@  Required parameters:
 - pinctrl-0: 		List of phandles pointing to pin configuration nodes
 			for PWM module.
 			For Pinctrl properties, please refer to [1].
-- clock-names: 		Set to "pwm".
+- clock-names: 		Valid entries are "pwm" and/or "capture".
 - clocks: 		phandle of the clock used by the PWM module.
 			For Clk properties, please refer to [2].
+- interrupts:		IRQ for the Capture device
 
 Optional properties:
-- st,pwm-num-chan:	Number of available channels. If not passed, the driver
-			will consider single channel by default.
+- st,pwm-num-devs:	Number of available PWM channels.  Default is 0.
+- st,capture-num-devs:	Number of available Capture channels.  Default is 0.
 
 [1] Documentation/devicetree/bindings/pinctrl/pinctrl-bindings.txt
 [2] Documentation/devicetree/bindings/clock/clock-bindings.txt
@@ -37,5 +38,6 @@  pwm1: pwm@fe510000 {
 		     &pinctrl_pwm1_chan3_default>;
 	clocks = <&clk_sysin>;
 	clock-names = "pwm";
-	st,pwm-num-chan = <4>;
+	st,pwm-num-devs = <4>;
+	st,capture-num-devs = <2>;
 };