Re: [PATCH 09/27] drm/rockchip: dw_hdmi: Set cur_ctr to 0 always

[Sascha Hauer <s.hauer@pengutronix.de>]

On Wed, Jan 26, 2022 at 07:42:48AM -0800, Doug Anderson wrote:
> Hi,
> 
> On Wed, Jan 26, 2022 at 6:58 AM Sascha Hauer <s.hauer@pengutronix.de> wrote:
> >
> > From: Douglas Anderson <dianders@chromium.org>
> >
> > Jitter was improved by lowering the MPLL bandwidth to account for high
> > frequency noise in the rk3288 PLL.  In each case MPLL bandwidth was
> > lowered only enough to get us a comfortable margin.  We believe that
> > lowering the bandwidth like this is safe given sufficient testing.
> >
> > Changes since v3:
> > - new patch
> >
> > Signed-off-by: Douglas Anderson <dianders@chromium.org>
> > Signed-off-by: Yakir Yang <ykk@rock-chips.com>
> > (am from https://patchwork.kernel.org/patch/9223301/)
> 
> Probably remove the "am from" line? It's not standard in upstream and
> that link doesn't seem to go anywhere anymore...
> 
> 
> > Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
> > ---
> >  drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c | 16 ++--------------
> >  1 file changed, 2 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > index c44eb4d2e2d5..77f82a4fd027 100644
> > --- a/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > +++ b/drivers/gpu/drm/rockchip/dw_hdmi-rockchip.c
> > @@ -176,20 +176,8 @@ static const struct dw_hdmi_mpll_config rockchip_mpll_cfg[] = {
> >  static const struct dw_hdmi_curr_ctrl rockchip_cur_ctr[] = {
> >         /*      pixelclk    bpp8    bpp10   bpp12 */
> >         {
> > -               40000000,  { 0x0018, 0x0018, 0x0018 },
> > -       }, {
> > -               65000000,  { 0x0028, 0x0028, 0x0028 },
> > -       }, {
> > -               66000000,  { 0x0038, 0x0038, 0x0038 },
> > -       }, {
> > -               74250000,  { 0x0028, 0x0038, 0x0038 },
> > -       }, {
> > -               83500000,  { 0x0028, 0x0038, 0x0038 },
> > -       }, {
> > -               146250000, { 0x0038, 0x0038, 0x0038 },
> > -       }, {
> > -               148500000, { 0x0000, 0x0038, 0x0038 },
> > -       }, {
> > +               600000000, { 0x0000, 0x0000, 0x0000 },
> > +       },  {
> 
> This is what we did for rk3288. I can't personally vouch for the
> effects on other SoCs.

Fair enough. Rockchip has this patch in their downstream Kernel, so I am
confident it works on SoCs newer as the rk3288 as well. I don't know how
much they care about the older SoCs, but it seems there is only the
rk3228 that is older than the rk3288 that is supported by this driver.

Sascha

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