linux-kernel - [PATCH v3 4/6] drm/msm/dsi: add a comment to explain pkt_per

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Date: Wed, 03 Apr 2024 17:11:00 +0800
From: Jun Nie <jun.nie@...aro.org>
To: Rob Clark <robdclark@...il.com>, 
 Abhinav Kumar <quic_abhinavk@...cinc.com>, 
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>, Sean Paul <sean@...rly.run>, 
 Marijn Suijten <marijn.suijten@...ainline.org>, 
 David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
 Jessica Zhang <quic_jesszhan@...cinc.com>, Vinod Koul <vkoul@...nel.org>
Cc: linux-arm-msm@...r.kernel.org, dri-devel@...ts.freedesktop.org, 
 freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
 Jun Nie <jun.nie@...aro.org>, Jonathan Marek <jonathan@...ek.ca>
Subject: [PATCH v3 4/6] drm/msm/dsi: add a comment to explain pkt_per_line
 encoding

From: Jonathan Marek <jonathan@...ek.ca>

Make it clear why the pkt_per_line value is being "divided by 2".

Signed-off-by: Jonathan Marek <jonathan@...ek.ca>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
Signed-off-by: Jun Nie <jun.nie@...aro.org>
---
 drivers/gpu/drm/msm/dsi/dsi_host.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
index 80ea4f1d8274..b0507a42ee6a 100644
--- a/drivers/gpu/drm/msm/dsi/dsi_host.c
+++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
@@ -886,7 +886,11 @@ static void dsi_update_dsc_timing(struct msm_dsi_host *msm_host, bool is_cmd_mod
 	/* DSI_VIDEO_COMPRESSION_MODE & DSI_COMMAND_COMPRESSION_MODE
 	 * registers have similar offsets, so for below common code use
 	 * DSI_VIDEO_COMPRESSION_MODE_XXXX for setting bits
+	 *
+	 * pkt_per_line is log2 encoded, >>1 works for supported values (1,2,4)
 	 */
+	if (pkt_per_line > 4)
+		drm_warn(msm_host->dev, "pkt_per_line too big");
 	reg |= DSI_VIDEO_COMPRESSION_MODE_CTRL_PKT_PER_LINE(pkt_per_line >> 1);
 	reg |= DSI_VIDEO_COMPRESSION_MODE_CTRL_EOL_BYTE_NUM(eol_byte_num);
 	reg |= DSI_VIDEO_COMPRESSION_MODE_CTRL_EN;

-- 
2.34.1