drm/msm/mdp5: Do not multiply vclk line count by 100

stable inclusion
from stable-5.10.36
commit 6e4ae9b0eb23378d993b17967fadd0990a2e8b10
bugzilla: 51867
CVE: NA

--------------------------------

[ Upstream commit 377569f8 ]

Neither vtotal nor drm_mode_vrefresh contain a value that is
premultiplied by 100 making the x100 variable name incorrect and
resulting in vclks_line to become 100 times larger than it is supposed
to be.  The hardware counts 100 clockticks too many before tearcheck,
leading to severe panel issues on at least the Sony Xperia lineup.

This is likely an artifact from the original MDSS DSI panel driver where
the calculation [1] corrected for a premultiplied reference framerate by
100 [2].  It does not appear that the above values were ever
premultiplied in the history of the DRM MDP5 driver.

With this change applied the value written to the SYNC_CONFIG_VSYNC
register is now identical to downstream kernels.

[1]: https://source.codeaurora.org/quic/la/kernel/msm-3.18/tree/drivers/video/msm/mdss/mdss_mdp_intf_cmd.c?h=LA.UM.8.6.c26-02400-89xx.0#n288
[2]: https://source.codeaurora.org/quic/la/kernel/msm-3.18/tree/drivers/video/msm/mdss/mdss_dsi_panel.c?h=LA.UM.8.6.c26-02400-89xx.0#n1648Reviewed-by: NAngeloGioacchino Del Regno <angelogioacchino.delregno@somainline.org>
Signed-off-by: NMarijn Suijten <marijn.suijten@somainline.org>
Link: https://lore.kernel.org/r/20210406214726.131534-3-marijn.suijten@somainline.orgSigned-off-by: NRob Clark <robdclark@chromium.org>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NWeilong Chen <chenweilong@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/gpu/drm/msm/disp/mdp5/mdp5_cmd_encoder.c

@@ -20,7 +20,7 @@ static int pingpong_tearcheck_setup(struct drm_encoder *encoder,
 {
 	struct mdp5_kms *mdp5_kms = get_kms(encoder);
 	struct device *dev = encoder->dev->dev;
-	u32 total_lines_x100, vclks_line, cfg;
+	u32 total_lines, vclks_line, cfg;
 	long vsync_clk_speed;
 	struct mdp5_hw_mixer *mixer = mdp5_crtc_get_mixer(encoder->crtc);
 	int pp_id = mixer->pp;
@@ -30,8 +30,8 @@ static int pingpong_tearcheck_setup(struct drm_encoder *encoder,
 		return -EINVAL;
 	}
 
-	total_lines_x100 = mode->vtotal * drm_mode_vrefresh(mode);
-	if (!total_lines_x100) {
+	total_lines = mode->vtotal * drm_mode_vrefresh(mode);
+	if (!total_lines) {
 		DRM_DEV_ERROR(dev, "%s: vtotal(%d) or vrefresh(%d) is 0\n",
 			      __func__, mode->vtotal, drm_mode_vrefresh(mode));
 		return -EINVAL;
@@ -43,7 +43,7 @@ static int pingpong_tearcheck_setup(struct drm_encoder *encoder,
 							vsync_clk_speed);
 		return -EINVAL;
 	}
-	vclks_line = vsync_clk_speed * 100 / total_lines_x100;
+	vclks_line = vsync_clk_speed / total_lines;
 
 	cfg = MDP5_PP_SYNC_CONFIG_VSYNC_COUNTER_EN
 		| MDP5_PP_SYNC_CONFIG_VSYNC_IN_EN;