[PATCH v6 2/5] drm/vc4: Avoid using vrefresh==0 mode in DSI htotal math.

Eric Anholt
2017-08-15T23:53:05Z

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.

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 eb787eed8abe..2516cd3a1d87 100644
--- a/drivers/gpu/drm/vc4/vc4_dsi.c
+++ b/drivers/gpu/drm/vc4/vc4_dsi.c
@@ -862,7 +862,8 @@ static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
adjusted_mode->clock = pixel_clock_hz / 1000;

/* 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;

--
2.14.1