From c8a570443943304cac2e4186dbce6989b6c2b8b5 Mon Sep 17 00:00:00 2001
From: Linus Walleij <linus.walleij@linaro.org>
Date: Tue, 8 Jun 2021 23:33:18 +0200
Subject: [PATCH] drm/mcde: Fix off by 10^3 in calculation
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Git-commit: c8a570443943304cac2e4186dbce6989b6c2b8b5
Patch-mainline: v5.13-rc6
References: git-fixes
The calclulation of how many bytes we stuff into the
DSI pipeline for video mode panels is off by three
orders of magnitude because we did not account for the
fact that the DRM mode clock is in kilohertz rather
than hertz.
This used to be:
drm_mode_vrefresh(mode) * mode->htotal * mode->vtotal
which would become for example for s6e63m0:
60 x 514 x 831 = 25628040 Hz, but mode->clock is
25628 as it is in kHz.
This affects only the Samsung GT-I8190 "Golden" phone
right now since it is the only MCDE device with a video
mode display.
Curiously some specimen work with this code and wild
settings in the EOL and empty packets at the end of the
display, but I have noticed an eeire flicker until now.
Others were not so lucky and got black screens.
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reported-by: Stephan Gerhold <stephan@gerhold.net>
Fixes: 920dd1b1425b ("drm/mcde: Use mode->clock instead of reverse calculating it from the vrefresh")
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Tested-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Stephan Gerhold <stephan@gerhold.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20210608213318.3897858-1-linus.walleij@linaro.org
Acked-by: Takashi Iwai <tiwai@suse.de>
---
drivers/gpu/drm/mcde/mcde_dsi.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/gpu/drm/mcde/mcde_dsi.c b/drivers/gpu/drm/mcde/mcde_dsi.c
index b3fd3501c412..5275b2723293 100644
--- a/drivers/gpu/drm/mcde/mcde_dsi.c
+++ b/drivers/gpu/drm/mcde/mcde_dsi.c
@@ -577,7 +577,7 @@ static void mcde_dsi_setup_video_mode(struct mcde_dsi *d,
* porches and sync.
*/
/* (ps/s) / (pixels/s) = ps/pixels */
- pclk = DIV_ROUND_UP_ULL(1000000000000, mode->clock);
+ pclk = DIV_ROUND_UP_ULL(1000000000000, (mode->clock * 1000));
dev_dbg(d->dev, "picoseconds between two pixels: %llu\n",
pclk);
--
2.26.2