Boris Brezillon <boris.brezillon@xxxxxxxxxxxxxxxxxx> writes: > On Tue, 18 Jul 2017 14:05:05 -0700 > Eric Anholt <eric@xxxxxxxxxx> wrote: > >> 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@xxxxxxxxxx> >> --- >> 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); > > Hm, I'm not sure I understand this. Shouldn't we have something like: > > adjusted_mode->htotal = (adjusted_mode->clock * mode->htotal) / > mode->clock; > > Is there a reason for doing '+ 1' when you calculate the adjusted > pixel clock rate but not here? We're actually expecting to get within epsilon of pixel_clock_hz, but we have to bump our clk_set_rate() to a higher value because the clock driver will give you a bad divider if you ask for anything less than the rate it can provide. How about I don't increment the adjusted_mode->clock (since it'll be userspace visible I think), and instead move that and the "Round up" comment to the clk_set_rate()?
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