linux-kernel - Re: [PATCH v9 07/11] dt-bindings: pwm: pwm-mediatek: add a property "num-pwms"

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:   Mon, 23 Sep 2019 15:36:26 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Sam Shih <sam.shih@...iatek.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>, linux-pwm@...r.kernel.org,
        Ryder Lee <ryder.lee@...iatek.com>, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        John Crispin <john@...ozen.org>,
        Matthias Brugger <matthias.bgg@...il.com>
Subject: Re: [PATCH v9 07/11] dt-bindings: pwm: pwm-mediatek: add a property
 "num-pwms"

On Mon, Sep 23, 2019 at 11:20:57AM +0800, Sam Shih wrote:
> On Sat, 2019-09-21 at 02:21 +0200, Thierry Reding wrote:
> > On Fri, Sep 20, 2019 at 06:49:07AM +0800, Sam Shih wrote:
> > > From: Ryder Lee <ryder.lee@...iatek.com>
> > > 
> > > This adds a property "num-pwms" in example so that we could
> > > specify the number of PWM channels via device tree.
> > > 
> > > Signed-off-by: Ryder Lee <ryder.lee@...iatek.com>
> > > Signed-off-by: Sam Shih <sam.shih@...iatek.com>
> > > Reviewed-by: Matthias Brugger <matthias.bgg@...il.com>
> > > Acked-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> > > ---
> > > Changes since v6:
> > > Follow reviewers's comments:
> > > - The subject should indicate this is for Mediatek
> > > 
> > > Changes since v5:
> > > - Add an Acked-by tag
> > > - This file is original v4 patch 5/10
> > > (https://patchwork.kernel.org/patch/11102577/)
> > > 
> > > ---
> > >  Documentation/devicetree/bindings/pwm/pwm-mediatek.txt | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > 
> > You failed to address Rob's questions repeatedly and I agree with him
> > that you can just as easily derive the number of PWMs from the specific
> > compatible string. I won't be applying this and none of the patches that
> > depend on it.
> > 
> 
> Hi, 
> 
> Thanks for getting back to me.
> 
> New pwm driver (patch 04/11 : "pwm: mediatek: allocate the clks array
> dynamically") can support different variants with different number of
> PWMs by the new property <num-pwms>
> 
> For example:
> 1. Use "num-pwms" = <2> and assign clocks pwm1, pwm2 for mt7622
> 2. Use "num-pwms" = <6> and assign clocks pwm1, pwm2, pwm3, pwm4, pwm5,
> pwm6 for mt7622.
> 
> If we just as easily derive the number of PWMs from the specific
> compatible string in this document:
> 
>    - "pwm1-6": the six per PWM clocks for mt7622
>    
> This looks like all "pwm1", "pwm2", "pwm3", "pwm4", "pwm5", "pwm6" is
> required property in DT, It doesn't make sense.

I don't understand. Why doesn't that make sense? If your hardware block
has 6 PWMs and each can be driven by its own clock, then you need to
provide references for each of those clocks, otherwise you won't be able
to use them.

>    
> So we removed those descriptions and added  
> 
>    - "pwm1-N": the PWM clocks for each channel 
>    
>    
> But the max number of clocks from the compatible string are still
> important information that should be provide in this document.
> 
> 
> What do you think of this?
> 
>    - "pwm1-N": per PWM clocks for mt2712, the max number of PWM channels
> is 8
> 
>    - "pwm1-N": per PWM clocks for mt7622, the max number of PWM channels
> is 6
> 
>    - "pwm1-N": per PWM clocks for mt7623, the max number of PWM channels
> is 5

That's what's in the bindings already, isn't it?

	 - clocks: phandle and clock specifier of the PWM reference clock.
	 - clock-names: must contain the following, except for MT7628 which
			has no clocks
	   - "top": the top clock generator
	   - "main": clock used by the PWM core
	   - "pwm1-8": the eight per PWM clocks for mt2712
	   - "pwm1-6": the six per PWM clocks for mt7622
	   - "pwm1-5": the five per PWM clocks for mt7623

Note that the description of the "clocks" property isn't quite accurate.
It should be something like:

	- clocks: One phandle and clock specifier for each entry in the
	          "clock-names" property.

In the above you clearly describe which PWMs you have to specify for
each generation of the hardware block.

> 
>    where N starting from 1 to the maximum number of PWM channels
>    - num-pwms: the number of PWM channels.

That's redundant information. The specific number of PWMs in already
implied by the compatible string, so you don't need to duplicate that
information here.

Thierry

Download attachment "signature.asc" of type "application/pgp-signature" (834 bytes)