linux-kernel - Re: [PATCH] firmware: meson-sm: use generic compatible

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Date:   Fri, 20 Oct 2017 14:34:06 -0500
From:   Rob Herring <robh@...nel.org>
To:     Jerome Brunet <jbrunet@...libre.com>
Cc:     Kevin Hilman <khilman@...libre.com>,
        Carlo Caione <carlo@...one.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        linux-amlogic@...ts.infradead.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] firmware: meson-sm: use generic compatible

On Fri, Oct 20, 2017 at 3:30 AM, Jerome Brunet <jbrunet@...libre.com> wrote:
> On Thu, 2017-10-19 at 16:18 -0500, Rob Herring wrote:
>> On Thu, Oct 19, 2017 at 5:25 AM, Kevin Hilman <khilman@...libre.com> wrote:
>> > Rob Herring <robh@...nel.org> writes:
>> >
>> > > On Thu, Oct 12, 2017 at 03:47:43PM +0200, Jerome Brunet wrote:
>> > > > The meson secure monitor seems to be compatible with more SoCs than
>> > > > initially thought. Let's use the most generic compatible he have in
>> > > > DT instead of the gxbb specific one
>> > > >
>> > > > Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
>> > > > ---
>> > > >  Documentation/devicetree/bindings/firmware/meson/meson_sm.txt | 4 ++--
>> > > >  drivers/firmware/meson/meson_sm.c                             | 4 ++--
>> > > >  2 files changed, 4 insertions(+), 4 deletions(-)
>> > >
>> > > Seems like a pointless, not backwards compatible change to me.
>> >
>> > I've verified that it's backwards compatible with existing upstream DTs.
>>
>> Perhaps if you all are documenting only what the driver uses, not what
>> the dts can have as Jerome said.
>>
>> > > end, it's just a string to match on. Who cares what the string is.
>> >
>> > As platform maintiner, I very much care what the strings are and I want
>> > it to be coherent with the platform generic names, and I want the
>> > SoC-specific strings to correspond to the actual SoC names.
>>
>> The most specific compatible should be, absolutely. The fallbacks can
>> be anything really. Ideally, they are the compatible string for the
>> 1st SoC with "the same" compatible IP. Could be another vendor
>> entirely even because mergers happen.
>
> Then what's your problem with these patches again ?

Removal of the SoC specific compatible and breaking compatibility.
Kevin says compatibility is not broken, but it obviously it based on
the example and the driver change. So that can only mean your dts file
doesn't match the example.

> I am just asking the driver to match the generic binding instead of the SoC
> specific, because we are also using it on other SoC, as explain in the patch
> comment. Does not seems that "pointless" to me.
>
> Right now the driver match only on: vendor,soc-one
> in dts, we have compatible = "vendor,family", "vendor,soc-one"

That's backwards if I understand this right. It should be most
specific first, but that's a separate issue.

> but it is compatible with soc-two as well.
> to match we would have to put "vendor,soc-one" as well which is a mess

Why? That's how DT works and every other platform follows. Either you have:

"vendor,soc-one", "vendor,family"
"vendor,soc-two", "vendor,family"

or

"vendor,soc-one"
"vendor,soc-two", "vendor,soc-one"

The latter is how DT has existed and worked for 20+ years. The former
is what we allow because for some reason people have such an aversion
to saying soc2 is compatible with soc1.

Either one is fine, but the documentation must be clear what the
constraints are for the dts file. For example, "vendor,soc-two" or
"vendor,family" alone are not valid. There's plenty of examples to
follow. Renesas is one using "vendor,family" extensively.

> By expressing correctly what the driver is compatible with, "vendor,family"
> we can dts that makes sense for soc-two as well
> compatible = "vendor,family", "vendor,soc-two"

Binding docs may live in the kernel, but they are separate from
drivers. They describe the constraints of the dts files. There's no
reason to document what the driver wants because I can read the driver
source. I can't say the same thing about the dts file. The dts may not
come from the kernel and one dts file is not all possible options for
a given binding.

Rob