linux-kernel - Re: [PATCH 1/2] drm/msm/dp: Disable wide bus support for SDM845

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Message-ID: <vl6cfjpckgndu5nacw3o5wvdfwaijactokby6q2lywcdccicgz@k27my3352m2k>
Date: Wed, 12 Feb 2025 11:03:39 +0100
From: Marijn Suijten <marijn.suijten@...ainline.org>
To: "James A. MacInnes" <james.a.macinnes@...il.com>
Cc: linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	robdclark@...il.com, quic_abhinavk@...cinc.com, dmitry.baryshkov@...aro.org, 
	sean@...rly.run, airlied@...il.com, simona@...ll.ch
Subject: Re: [PATCH 1/2] drm/msm/dp: Disable wide bus support for SDM845

On 2025-02-11 19:42:24, James A. MacInnes wrote:
> SDM845 DPU hardware is rev 4.0.0 per hardware document.

Just checking: version 4.0.0 is not named in the code that you're changing: are
you mentioning this because the patch you're fixing here [1] says that widebus
is "recommended" on 5.x.x which includes sc7180, yet didn't account for that
sc7180_dp_descs also being used in the SDM845 compatible which is 4.0.0?  That
is something worth mentioning in the patch description.

[1]: https://lore.kernel.org/linux-arm-msm/20240730195012.2595980-1-quic_abhinavk@quicinc.com/

> 
> Incorrect setting caused inop displayport.

Inop doesn't seem to be a common abbreviation, there's enough space to spell
out "inoperative".  And spend some more words on _why_ this is an "incorrect
setting" in the first place  (based on the suggestion above)?

I am trying to remember the details from the original widebus series: we
discussed that the INTF_CFG2_DATABUS_WIDEN flag was available starting with DPU
4.0.0 (IIRC, cannot find the source), yet the DSI host only supports it from
6G v2.5 onwards (SC7280 and up?) [2].  Seems a similar limitation applies to
DP hosts.

[2]: https://lore.kernel.org/linux-arm-msm/20230822-add-widebus-support-v4-4-9dc86083d6ea@quicinc.com/

> Corrected by separating SDM845 to own descriptor.

its own*

> 
> Fixes: c7c412202623 ("drm/msm/dp: enable widebus on all relevant chipsets")
> 

No need for empty lines between trailing tags.

> Signed-off-by: James A. MacInnes <james.a.macinnes@...il.com>
> ---
>  drivers/gpu/drm/msm/dp/dp_display.c | 7 ++++++-
>  1 file changed, 6 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/msm/dp/dp_display.c b/drivers/gpu/drm/msm/dp/dp_display.c
> index aff51bb973eb..2cbdbf85a85c 100644
> --- a/drivers/gpu/drm/msm/dp/dp_display.c
> +++ b/drivers/gpu/drm/msm/dp/dp_display.c
> @@ -126,6 +126,11 @@ static const struct msm_dp_desc msm_dp_desc_sa8775p[] = {
>  	{}
>  };
>  
> +static const struct msm_dp_desc msm_dp_desc_sdm845[] = {
> +	{ .io_start = 0x0ae90000, .id = MSM_DP_CONTROLLER_0, .wide_bus_supported = false },

We can probably drop the assignment, it'll be false/0 by default.

- Marijn

> +	{}
> +};
> +
>  static const struct msm_dp_desc msm_dp_desc_sc7180[] = {
>  	{ .io_start = 0x0ae90000, .id = MSM_DP_CONTROLLER_0, .wide_bus_supported = true },
>  	{}
> @@ -178,7 +183,7 @@ static const struct of_device_id msm_dp_dt_match[] = {
>  	{ .compatible = "qcom,sc8180x-edp", .data = &msm_dp_desc_sc8180x },
>  	{ .compatible = "qcom,sc8280xp-dp", .data = &msm_dp_desc_sc8280xp },
>  	{ .compatible = "qcom,sc8280xp-edp", .data = &msm_dp_desc_sc8280xp },
> -	{ .compatible = "qcom,sdm845-dp", .data = &msm_dp_desc_sc7180 },
> +	{ .compatible = "qcom,sdm845-dp", .data = &msm_dp_desc_sdm845 },
>  	{ .compatible = "qcom,sm8350-dp", .data = &msm_dp_desc_sc7180 },
>  	{ .compatible = "qcom,sm8650-dp", .data = &msm_dp_desc_sm8650 },
>  	{ .compatible = "qcom,x1e80100-dp", .data = &msm_dp_desc_x1e80100 },
> -- 
> 2.43.0
>