linux-kernel - Re: [PATCH v2 1/3] drm/msm/dsi: Use existing per-interface slice count in DSC timing

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Message-ID: <guhjhtm54xttaech3jpnsqqzfevadure6clecb5elruxxd6trd@sunww3caiial>
Date: Tue, 11 Feb 2025 05:42:06 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Marijn Suijten <marijn.suijten@...ainline.org>
Cc: Rob Clark <robdclark@...il.com>, 
	Abhinav Kumar <quic_abhinavk@...cinc.com>, Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>, 
	Vinod Koul <vkoul@...nel.org>, Simona Vetter <simona@...ll.ch>, linux-arm-msm@...r.kernel.org, 
	dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	Jordan Crouse <jordan@...micpenguin.net>, ~postmarketos/upstreaming@...ts.sr.ht, 
	AngeloGioacchino Del Regno <angelogioacchino.delregno@...labora.com>, Martin Botka <martin.botka@...ainline.org>, 
	Jami Kettunen <jami.kettunen@...ainline.org>, Konrad Dybcio <konrad.dybcio@....qualcomm.com>
Subject: Re: [PATCH v2 1/3] drm/msm/dsi: Use existing per-interface slice
 count in DSC timing

On Sun, Feb 09, 2025 at 10:42:52PM +0100, Marijn Suijten wrote:
> When configuring the timing of DSI hosts (interfaces) in
> dsi_timing_setup() all values written to registers are taking
> bonded-mode into account by dividing the original mode width by 2
> (half the data is sent over each of the two DSI hosts), but the full
> width instead of the interface width is passed as hdisplay parameter to
> dsi_update_dsc_timing().
> 
> Currently only msm_dsc_get_slices_per_intf() is called within
> dsi_update_dsc_timing() with the `hdisplay` argument which clearly
> documents that it wants the width of a single interface (which, again,
> in bonded DSI mode is half the total width of the mode) resulting in all
> subsequent values to be completely off.
> 
> However, as soon as we start to pass the halved hdisplay
> into dsi_update_dsc_timing() we might as well discard
> msm_dsc_get_slices_per_intf() since the value it calculates is already
> available in dsc->slice_count which is per-interface by the current
> design of MSM DPU/DSI implementations and their use of the DRM DSC
> helpers.
> 
> Fixes: 08802f515c3c ("drm/msm/dsi: Add support for DSC configuration")
> Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
> ---
>  drivers/gpu/drm/msm/dsi/dsi_host.c   |  8 ++++----
>  drivers/gpu/drm/msm/msm_dsc_helper.h | 11 -----------
>  2 files changed, 4 insertions(+), 15 deletions(-)
> 

Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>

-- 
With best wishes
Dmitry