linux-kernel - Re: [PATCH 1/3] dt-bindings: pwm: kona: Add new compatible for new version pwm-kona

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Date:   Sat, 12 Jan 2019 16:05:15 +0100
From:   Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
To:     Scott Branden <scott.branden@...adcom.com>
Cc:     Sheetal Tigadoli <sheetal.tigadoli@...adcom.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Florian Fainelli <f.fainelli@...il.com>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        bcm-kernel-feedback-list@...adcom.com, linux-pwm@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        Praveen Kumar B <praveen.b@...adcom.com>
Subject: Re: [PATCH 1/3] dt-bindings: pwm: kona: Add new compatible for new
 version pwm-kona

Hello Scott,

On Fri, Jan 11, 2019 at 01:28:45PM -0800, Scott Branden wrote:
> On 2019-01-11 12:48 p.m., Uwe Kleine-König wrote:
> > On Fri, Jan 11, 2019 at 10:51:14AM +0530, Sheetal Tigadoli wrote:
> > > From: Praveen Kumar B <praveen.b@...adcom.com>
> > > 
> > > Add new compatible string for new version of pwm-kona
> > > 
> > > Signed-off-by: Praveen Kumar B <praveen.b@...adcom.com>
> > > Reviewed-by: Ray Jui <ray.jui@...adcom.com>
> > > Reviewed-by: Scott Branden <scott.branden@...adcom.com>
> > > Signed-off-by: Sheetal Tigadoli <sheetal.tigadoli@...adcom.com>
> > > ---
> > >   Documentation/devicetree/bindings/pwm/brcm,kona-pwm.txt | 2 +-
> > >   1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/Documentation/devicetree/bindings/pwm/brcm,kona-pwm.txt b/Documentation/devicetree/bindings/pwm/brcm,kona-pwm.txt
> > > index 8eae9fe..d37f697 100644
> > > --- a/Documentation/devicetree/bindings/pwm/brcm,kona-pwm.txt
> > > +++ b/Documentation/devicetree/bindings/pwm/brcm,kona-pwm.txt
> > > @@ -3,7 +3,7 @@ Broadcom Kona PWM controller device tree bindings
> > >   This controller has 6 channels.
> > >   Required Properties :
> > > -- compatible: should contain "brcm,kona-pwm"
> > > +- compatible: should contain "brcm,kona-pwm" or "brcm,kona-pwm-v2"
> > Is v2 used on a newer generation of kona SoCs? On i.MX these variants
> > are usually named after the first SoC that came with the new variant. Is
> > this sensible here, too?
> 
> It doesn't make as much sense here as different revs of the IP block are
> picked up based on various decisions.
> 
> A new SoC could decide to use an old version.

IMHO this is no reason to not use the name of the oldest SoC with this
variant. I don't know how the SoC names are in the broadcom family, but
if they were (in order of age, oldest first):

	ant
	bear
	crocodile

and ant and crocodile use the same IP block we would have

a) with v1, v2:

	ant:
		compatible = "brcm,kona-pwm-v1";
	bear:
		compatible = "brcm,kona-pwm-v2";
	crocodile:
		compatible = "brcm,kona-pwm-v1";

; and 

b) with the SoC naming:

	ant:
		compatible = "brcm,kona-ant-pwm";
	bear:
		compatible = "brcm,kona-bear-pwm";
	crocodile:
		compatible = "brcm,kona-crocodile-pwm", "brcm,kona-ant-pwm";

(If you want, drop "brcm,kona-crocodile-pwm", but keeping it is more
defensive.) 

I like b) (with "...-crocodile-...") better than a). crocodile using
"...-ant-..." is not more ugly than crocodile using "...-v1". This is
also a tad more robust because if broadcom releases kona-dolphin and
someone finds a minor difference between the IPs used on ant and
crocodile it depends on the order of these events who gets v3, while
with the SoC naming the result is clear.

(OK, and given that "brcm,kona-pwm" is already fixed, both approaches
need slight adaption, but I guess you still get what I meant.)

Best regards
Uwe


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Pengutronix e.K.                           | Uwe Kleine-König            |
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