On Fri, 24 Aug 2018 10:55:00 +0200 Peter Rosin <[email protected]> wrote:
> If the divider used to get the pixel-clock is small, the granularity > of the frequencies possible for the pixel-clock is quite coarse. E.g. > requesting a pixel-clock of 65MHz with a sys_clk of 132MHz results > in the divider being set to 3 ending up with 44MHz. > > By preferring the doubled sys_clk as base, the divider instead ends > up as 5 yielding a pixel-clock of 52.8Mhz, which is a definite > improvement. > > While at it, clamp the divider so that it does not overflow in case > it gets big. > > Signed-off-by: Peter Rosin <[email protected]> > --- > drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c | 16 ++++++++++------ > 1 file changed, 10 insertions(+), 6 deletions(-) > > diff --git a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > index c38a479ada98..71c9cd90d2ae 100644 > --- a/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > +++ b/drivers/gpu/drm/atmel-hlcdc/atmel_hlcdc_crtc.c > @@ -101,18 +101,22 @@ static void atmel_hlcdc_crtc_mode_set_nofb(struct > drm_crtc *c) > (adj->crtc_hdisplay - 1) | > ((adj->crtc_vdisplay - 1) << 16)); > > - cfg = 0; > + cfg = ATMEL_HLCDC_CLKSEL; > > - prate = clk_get_rate(crtc->dc->hlcdc->sys_clk); > + prate = 2 * clk_get_rate(crtc->dc->hlcdc->sys_clk); > mode_rate = adj->crtc_clock * 1000; > - if ((prate / 2) < mode_rate) { > - prate *= 2; > - cfg |= ATMEL_HLCDC_CLKSEL; > - } > > div = DIV_ROUND_UP(prate, mode_rate); > if (div < 2) > div = 2; I'm nitpicking, but can you add braces around the if() block? Looks good otherwise. > + else if (ATMEL_HLCDC_CLKDIV(div) & ~ATMEL_HLCDC_CLKDIV_MASK) { > + /* the divider ended up too big, try a lower base rate */ > + cfg &= ~ATMEL_HLCDC_CLKSEL; > + prate /= 2; > + div = DIV_ROUND_UP(prate, mode_rate); > + if (ATMEL_HLCDC_CLKDIV(div) & ~ATMEL_HLCDC_CLKDIV_MASK) > + div = ATMEL_HLCDC_CLKDIV_MASK; > + } > > cfg |= ATMEL_HLCDC_CLKDIV(div); > _______________________________________________ dri-devel mailing list [email protected] https://lists.freedesktop.org/mailman/listinfo/dri-devel
