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drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

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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.
v3: Simplify math now that adjusted_mode->clock isn't padded.
v4: Drop some parens.

Signed-off-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20170815234722.20700-2-eric@anholt.net
Reviewed-by: Andrzej Hajda <a.hajda@samsung.com>
This commit is contained in:
Eric Anholt 2017-08-15 16:47:19 -07:00
parent 9949b355dc
commit af2eca5320
1 changed files with 2 additions and 1 deletions
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3
drivers/gpu/drm/vc4/vc4_dsi.c
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@ -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 = adjusted_mode->clock * mode->htotal /
mode->clock;
adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;