linux-kernel - [PATCH v3 07/10] drm/msm/dsi: Disallow 8 BPC DSC configuration for alternative BPC values

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Message-Id: <20221009185150.461323-1-marijn.suijten@somainline.org>
Date:   Sun,  9 Oct 2022 20:51:46 +0200
From:   Marijn Suijten <marijn.suijten@...ainline.org>
To:     phone-devel@...r.kernel.org
Cc:     ~postmarketos/upstreaming@...ts.sr.ht,
        AngeloGioacchino Del Regno 
        <angelogioacchino.delregno@...ainline.org>,
        Konrad Dybcio <konrad.dybcio@...ainline.org>,
        Martin Botka <martin.botka@...ainline.org>,
        Jami Kettunen <jami.kettunen@...ainline.org>,
        Marijn Suijten <marijn.suijten@...ainline.org>,
        Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, Vinod Koul <vkoul@...nel.org>,
        Douglas Anderson <dianders@...omium.org>,
        Vladimir Lypak <vladimir.lypak@...il.com>,
        linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: [PATCH v3 07/10] drm/msm/dsi: Disallow 8 BPC DSC configuration for alternative BPC values

According to the `/* bpc 8 */` comment below only values for a
bits_per_component of 8 are currently hardcoded in place.  This is
further confirmed by downstream sources [1] containing different
constants for other BPC values (and different initial_offset too,
with an extra dependency on bits_per_pixel).  Prevent future mishaps by
explicitly disallowing any other bits_per_component value until the
right parameters are put in place and tested.

[1]: https://git.codelinaro.org/clo/la/platform/vendor/opensource/display-drivers/-/blob/DISPLAY.LA.2.0.r1-08000-WAIPIO.0/msm/sde_dsc_helper.c#L110-139

Signed-off-by: Marijn Suijten <marijn.suijten@...ainline.org>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 68c39debc22f..7e6b7e506ae8 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -1774,6 +1774,11 @@ static int dsi_populate_dsc_params(struct drm_dsc_config *dsc)
 {
 	int i;
 
+	if (dsc->bits_per_component != 8) {
+		DRM_DEV_ERROR(&msm_host->pdev->dev, "DSI does not support bits_per_component != 8 yet\n");
+		return -EOPNOTSUPP;
+	}
+
 	dsc->rc_model_size = 8192;
 	dsc->first_line_bpg_offset = 12;
 	dsc->rc_edge_factor = 6;
-- 
2.38.0