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From:   "Lad, Prabhakar" <prabhakar.csengg@gmail.com>
Date:   Mon, 17 Oct 2022 08:43:18 +0100
Message-ID: <CA+V-a8uO4gTAObT+gZ-rROD2xyTXYP6kxfihMbgfbw1W2zXdPg@mail.gmail.com>
Subject: Re: [PATCH v2 1/5] media: dt-bindings: ov5645: Convert OV5645 binding
 to a schema
To:     Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
Cc:     Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Rob Herring <robh@kernel.org>,
        Sakari Ailus <sakari.ailus@linux.intel.com>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@linaro.org>,
        Mauro Carvalho Chehab <mchehab@kernel.org>,
        Hans Verkuil <hverkuil@xs4all.nl>,
        Shawn Tu <shawnx.tu@intel.com>,
        Jacopo Mondi <jacopo@jmondi.org>, linux-media@vger.kernel.org,
        devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
        linux-renesas-soc@vger.kernel.org,
        Biju Das <biju.das.jz@bp.renesas.com>,
        Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
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On Sat, Oct 15, 2022 at 2:17 PM Krzysztof Kozlowski
<krzysztof.kozlowski@linaro.org> wrote:
>
> On 15/10/2022 01:54, Laurent Pinchart wrote:
> > Hi Rob,
> >
> > On Fri, Oct 14, 2022 at 04:40:29PM -0500, Rob Herring wrote:
> >> On Fri, Oct 14, 2022 at 10:27:53PM +0100, Lad, Prabhakar wrote:
> >>> On Fri, Oct 14, 2022 at 10:05 PM Rob Herring <robh+dt@kernel.org> wrote:
> >>>> On Fri, Oct 14, 2022 at 1:35 PM Prabhakar <prabhakar.csengg@gmail.com> wrote:
> >>>>>
> >>>>> From: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
> >>>>>
> >>>>> Convert the simple OV5645 Device Tree binding to json-schema.
> >>>>>
> >>>>> The previous binding marked the below properties as required which was a
> >>>>> driver requirement and not the device requirement so just drop them from
> >>>>> the required list during the conversion.
> >>>>> - clock-frequency
> >>>>> - enable-gpios
> >>>>> - reset-gpios
> >>>>>
> >>>>> Also drop the "clock-names" property as we have a single clock source for
> >>>>> the sensor and the driver has been updated to drop the clk referencing by
> >>>>> name.
> >>>>
> >>>> Driver requirements are the ABI!
> >>>>
> >>>> This breaks a kernel without the driver change and a DTB that has
> >>>> dropped the properties.
> >>>>
> >>> I already have a patch for the driver [0] which I missed to include
> >>> along with the series.
> >>
> >> You completely miss the point. Read the first sentence again. Changing
> >> driver requirements changes the ABI.
> >>
> >> This breaks the ABI. The driver patch does not help that.
> >
> > I'm not following you here. If the DT binding makes a mandatory property
> > optional, it doesn't break any existing platform. The only thing that
> > would not work is a new DT that doesn't contain the now optional
> > property combined with an older driver that makes it required. That's
> > not a regression, as it would be a *new* DT.
>
> You're right although in-tree DTS are now not compatible with older
> kernels. So it is not only about new DTS, it is about our kernel DTS
> which requires new kernel to work.
>
To confirm, we are ok dropping the clock-names property here right?

> DTS are exported and used by other systems, thus if someone blindly
> takes this new DTS without clock-names, his kernel/OS/bootloader might
> stop working.
>
> That is however a more relaxed requirement than kernel ABI against old DTS.
>
> >
> >>>> Also, with 'clock-names' dropped, you've just introduced a bunch of
> >>>> warnings on other people's platforms. Are you going to 'fix' all of
> >>>> them?
> >>>>
> >>> Yes I will fix them, once the patch driver patch [0] is merged in.
> >>
> >> Why? You are just making extra work. We have enough warnings as-is to
> >> fix.
> >
> > I agree that a DT binding change should patch all in-tree DTS to avoid
> > introducing new warnings.
>
> Yes.
>
OK, I'll send dts changes along with this patch series.

Cheers,
Prabhakar