linux-kernel - Re: [RFC PATCH] drm/msm/dpu1: Add a common DPU1 compatible

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Date:   Tue, 22 Feb 2022 05:26:03 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Konrad Dybcio <konrad.dybcio@...ainline.org>
Cc:     ~postmarketos/upstreaming@...ts.sr.ht, martin.botka@...ainline.org,
        angelogioacchino.delregno@...ainline.org,
        marijn.suijten@...ainline.org, jamipkettunen@...ainline.org,
        Rob Clark <robdclark@...il.com>, Sean Paul <sean@...rly.run>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Stephen Boyd <swboyd@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Kalyan Thota <quic_kalyant@...cinc.com>,
        Krishna Manikandan <quic_mkrishn@...cinc.com>,
        Yangtao Li <tiny.windzz@...il.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] drm/msm/dpu1: Add a common DPU1 compatible

Hi,

On Tue, 22 Feb 2022 at 04:26, Konrad Dybcio
<konrad.dybcio@...ainline.org> wrote:
>
> There is *almost no reason* to keep separate compatibles for different
> SoCs utilizing the DPU1 driver, as it checks the HW version at runtime.
>
> Introduce a common compatible, while not removing the old ones to keep
> old DT compatibility.

I don't quite like this idea. Specifying more or less exact
compatibility string gives us more flexibility.
Few recent usecases to mention:
- qcom,mdp5 compatibility. If we had soc-specific compatibilities, we
would be able to switch the drivers w/o changing the dts. With a
single compatibility we would have to change the dts if we were to
change one of the boards form mdp5 to dpu1.
- qcom,mdss-dsi-ctrl vs qcm2290. We have to add special compat string
to account for the different io addresses. If we were using
soc-specific compats, it would be one from many, not one vs many
usage.

>
> Signed-off-by: Konrad Dybcio <konrad.dybcio@...ainline.org>
> ---
> Bar some very very very unlikely edge cases (such as need for some random
> quick being applied to one SoC from a family that shares DPU hw rev, but
> not the others, there is little to no reason to keep adding compatibles
> that don't mean anything.
>
> If this change is cool, then the question about what to do with
> dt-bindings arises...
>
>  drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c | 3 +++
>  1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> index 47fe11a84a77..335018542a3a 100644
> --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_kms.c
> @@ -1348,6 +1348,9 @@ static const struct dev_pm_ops dpu_pm_ops = {
>  };
>
>  const struct of_device_id dpu_dt_match[] = {
> +       { .compatible = "qcom,dpu1" },
> +
> +       /* Legacy compatibles for old DTs */
>         { .compatible = "qcom,sdm845-dpu", },
>         { .compatible = "qcom,sc7180-dpu", },
>         { .compatible = "qcom,sc7280-dpu", },
> --
> 2.35.1
>


-- 
With best wishes
Dmitry