Re: [PATCH v2 1/3] drm: rockchip: hdmi: fix clock rounding code

[Doug Anderson <dianders@chromium.org>]

Hi,

On Tue, Sep 22, 2020 at 6:38 PM crj <algea.cao@rock-chips.com> wrote:
>
>
> 在 2020/9/23 4:31, Vicente Bergas 写道:
> > Under certain conditions vop_crtc_mode_fixup rounds the clock
> > 148500000 to 148501000 which leads to the following error:
> > dwhdmi-rockchip ff940000.hdmi: PHY configuration failed (clock 148501000)
> >
> > The issue was found on RK3399 booting with u-boot. U-boot configures the
> > display at 2560x1440 and then linux comes up with a black screen.
> > A workaround was to un-plug and re-plug the HDMI display.
> >
> > Signed-off-by: Vicente Bergas <vicencb@gmail.com>
> > Tested-by: Vicente Bergas <vicencb@gmail.com>
> > ---
> >   drivers/gpu/drm/rockchip/rockchip_drm_vop.c | 7 ++-----
> >   1 file changed, 2 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > index c80f7d9fd13f..92efbd899dee 100644
> > --- a/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > +++ b/drivers/gpu/drm/rockchip/rockchip_drm_vop.c
> > @@ -1176,12 +1176,9 @@ static bool vop_crtc_mode_fixup(struct drm_crtc *crtc,
> >        *
> >        * 2. Get the clock framework to round the rate for us to tell us
> >        *    what it will actually make.
> > -      *
> > -      * 3. Store the rounded up rate so that we don't need to worry about
> > -      *    this in the actual clk_set_rate().
> >        */
> >       rate = clk_round_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
> > -     adjusted_mode->clock = DIV_ROUND_UP(rate, 1000);
> > +     adjusted_mode->clock = rate / 1000;
> >
> >       return true;
> >   }
> > @@ -1380,7 +1377,7 @@ static void vop_crtc_atomic_enable(struct drm_crtc *crtc,
> >
> >       VOP_REG_SET(vop, intr, line_flag_num[0], vact_end);
> >
> > -     clk_set_rate(vop->dclk, adjusted_mode->clock * 1000);
> > +     clk_set_rate(vop->dclk, adjusted_mode->clock * 1000 + 999);
>
>
> In some RK platform, such as RK3328, dclk is generated by the INNO HDMI
> PHY PLL, which support
>
> frac divider can support any dclk frequency. And The PLL must use the
> exact clock to determine
>
> the PLL configuration. So adjusted_mode->clock * 1000 + 999 may cause
> INNO HDMI PHY PLL
>
> couldn't find the right configuration. INNO HDMI PHY's driver path is:
>
> drivers/phy/rockchip/phy-rockchip-inno-hdmi.c

I don't think you'll have a problem.  Assuming I'm looking at the
correct code, in the function inno_hdmi_phy_rk3228_clk_round_rate()
you've got "rate = (rate / 1000) * 1000".  I believe the clock
framework automatically calls round rate when someone tries to set the
rate, so this should clean the clock back up.

If I'm misunderstanding, please yell.

-Doug

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