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

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>

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index d1e0dc908048242749b92fcac689a3333ab5230d..04796d7d0fdbb441c09ecbd9b4fbce41a7831534 100644 (file)
--- 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 = 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;