diff options
| author | Peter Rosin <peda@axentia.se> | 2018-08-24 12:24:58 +0300 |
|---|---|---|
| committer | Boris Brezillon <boris.brezillon@bootlin.com> | 2018-08-27 22:13:01 +0300 |
| commit | 9946a3a9dbedaaacef8b7e94f6ac144f1daaf1de (patch) | |
| tree | e6a61224906265e8cf0e782423b16578111ed138 | |
| parent | 319711f982084b044d3dac6ae58e3d801ae4ca43 (diff) | |
| download | linux-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
| -rw-r--r-- | drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 12 |
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); |