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authorPeter Rosin <peda@axentia.se>2018-08-24 12:24:58 +0300
committerBoris Brezillon <boris.brezillon@bootlin.com>2018-08-27 22:13:01 +0300
commit9946a3a9dbedaaacef8b7e94f6ac144f1daaf1de (patch)
treee6a61224906265e8cf0e782423b16578111ed138 /drivers/gpu/drm/atmel-hlcdc
parent319711f982084b044d3dac6ae58e3d801ae4ca43 (diff)
downloadlinux-9946a3a9dbedaaacef8b7e94f6ac144f1daaf1de.tar.xz
drm/atmel-hlcdc: allow selecting a higher pixel-clock than requested
But only if the highest pixel-clock frequency lower than requested is significantly less accurate than 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 <peda@axentia.se> Signed-off-by: Boris Brezillon <boris.brezillon@bootlin.com> Link: https://patchwork.freedesktop.org/patch/msgid/20180824092458.13165-3-peda@axentia.se
Diffstat (limited to 'drivers/gpu/drm/atmel-hlcdc')
-rw-r--r--drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c12
1 files changed, 12 insertions, 0 deletions
diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
index ec209dec224d..229138130ce1 100644
--- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
+++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c
@@ -116,6 +116,18 @@ 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);