Re: [PATCH v4 4/7] drm/vc4: hdmi: Fix hdmi_enable_4kp60 detection

[maxime]

Hi Dave,

Thanks for your review

On Wed, Oct 26, 2022 at 04:36:04PM +0100, Dave Stevenson wrote:
> On Wed, 26 Oct 2022 at 16:27, Dave Stevenson
> <dave.stevenson@xxxxxxxxxxxxxxx> wrote:
> >
> > On Thu, 20 Oct 2022 at 10:14, <maxime@xxxxxxxxxx> wrote:
> > >
> > > In order to support higher HDMI frequencies, users have to set the
> > > hdmi_enable_4kp60 parameter in their config.txt file.
> > >
> > > We were detecting this so far by calling clk_round_rate() on the core
> > > clock with the frequency we're supposed to run at when one of those
> > > modes is enabled. Whether or not the parameter was enabled could then be
> > > inferred by the returned rate since the maximum clock rate reported by
> > > the firmware was one of the side effect of setting that parameter.
> > >
> > > However, the recent clock rework we did changed what clk_round_rate()
> > > was returning to always return the minimum allowed, and thus this test
> > > wasn't reliable anymore.
> > >
> > > Let's use the new clk_get_max_rate() function to reliably determine the
> > > maximum rate allowed on that clock and fix the 4k@60Hz output.
> > >
> > > Fixes: e9d6cea2af1c ("clk: bcm: rpi: Run some clocks at the minimum rate allowed")
> > > Signed-off-by: Maxime Ripard <maxime@xxxxxxxxxx>
> >
> > Reviewed-by: Dave Stevenson <dave.stevenson@xxxxxxxxxxxxxxx>
> >
> > > ---
> > >  drivers/gpu/drm/vc4/vc4_hdmi.c | 3 ++-
> > >  1 file changed, 2 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > index 64f9feabf43e..87961d4de5aa 100644
> > > --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> > > @@ -46,6 +46,7 @@
> > >  #include <linux/pm_runtime.h>
> > >  #include <linux/rational.h>
> > >  #include <linux/reset.h>
> > > +#include <soc/bcm2835/raspberrypi-clocks.h>
> > >  #include <sound/dmaengine_pcm.h>
> > >  #include <sound/hdmi-codec.h>
> > >  #include <sound/pcm_drm_eld.h>
> > > @@ -3429,7 +3430,7 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data)
> > >
> > >         if (variant->max_pixel_clock == 600000000) {
> > >                 struct vc4_dev *vc4 = to_vc4_dev(drm);
> > > -               long max_rate = clk_round_rate(vc4->hvs->core_clk, 550000000);
> > > +               unsigned long max_rate = rpi_firmware_clk_get_max_rate(vc4->hvs->core_clk);
> 
> Actually minor nit:
> rpi_firmware_clk_get_max_rate returns an unsigned int.
> AFAICT we don't need the range of unsigned long in any subsequent
> code, so I think it could just be unsigned int here.
> 
> clk_round_rate returned a long, and therefore previously it did have to be that.

Yeah, I was actually two-minded about this.
rpi_firmware_clk_get_max_rate() indeed returns an unsigned long, because
that's what the firmware returns.

But the clock framework uses unsigned long to store all its frequencies,
and in our case here in clk_set_min_rate().

I don't mind changing it to unsigned int here if you prefer to, and if
you're fine with the rest of the patches I can fix it up while applying
the patches.

Maxime