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Subject[PATCH v5 1/6] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.
Date
The incoming mode might have a missing vrefresh field if it came from
drmModeSetCrtc(), which the kernel is supposed to calculate using
drm_mode_vrefresh(). We could either use that or the adjusted_mode's
original vrefresh value.

However, we can maintain a more exact vrefresh value (not just the
integer approximation), by scaling by the ratio of our clocks.

v2: Use math suggested by Andrzej Hajda instead.

Signed-off-by: Eric Anholt <eric@anholt.net>
---
drivers/gpu/drm/vc4/vc4_dsi.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index 629d372633e6..57213f4e3c72 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -866,7 +866,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
adjusted_mode->clock = pixel_clock_hz / 1000 + 1;

/* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
- adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * mode->vtotal);
+ adjusted_mode->htotal = (pixel_clock_hz / 1000 * mode->htotal /
+ mode->clock);
adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;

--
2.11.0
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