But only if the highest pixel-clock frequency lower than requested
is significantly much less accurate that the lowest frequency higher
than requested.
I pulled "10 times" as the discriminator out of the hat, and went with
that.
This is useful, if e.g. the target pixel-clock is 65MHz and the sys_clk
is 132MHz. In this case the highest possible pixel-clock lower than the
requested 65MHz is 52.8MHz, which is almost 20% off (and outside the
spec for the panel). The lowest possible pixel-clock higher than 65MHz
is 66MHz, which is a *much* better match, and only 1.5% off.
Signed-off-by: Peter Rosin <p...@axentia.se>
---
drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 13 +++++++++++++
1 file changed, 13 insertions(+)
diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
index 71c9cd90d2ae..0c2717ed4ac6 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
@@ -116,6 +116,19 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct drm_crtc
*c)
div = DIV_ROUND_UP(prate, mode_rate);
if (ATMEL_HLCDC_CLKDIV(div) & ~ATMEL_HLCDC_CLKDIV_MASK)
div = ATMEL_HLCDC_CLKDIV_MASK;
+ } else {
+ int div_low = prate / mode_rate;
+
+ if (div_low >= 2 &&
+ ((prate / div_low - mode_rate) <
+ 10 * (mode_rate - prate / div)))
+ /*
+ * At least 10 times better when
+ * using a higher frequency than
+ * requested, instead of a lower.
+ * So, go with that.
+ */
+ div = div_low;
}
cfg |= ATMEL_HLCDC_CLKDIV(div);
--
2.11.0
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