Hi Maxime,
On Mon, Nov 25, 2024 at 05:00:56PM +0100, Maxime Ripard wrote:
> Hi Sean,
>
> On Mon, Nov 25, 2024 at 02:49:26PM +0100, Sean Nyekjaer wrote:
> > Check if the required pixel clock is in within .5% range of the
> > desired pixel clock.
> > This will match the requirement for HDMI where a .5% tolerance is allowed.
> >
> > Signed-off-by: Sean Nyekjaer <sean@xxxxxxxxxx>
> > ---
> > drivers/gpu/drm/drm_modes.c | 34 ++++++++++++++++++++++++++++++++++
> > include/drm/drm_modes.h | 2 ++
> > 2 files changed, 36 insertions(+)
> >
> > diff --git a/drivers/gpu/drm/drm_modes.c b/drivers/gpu/drm/drm_modes.c
> > index 6ba167a3346134072d100af0adbbe9b49e970769..4068b904759bf80502efde6e4d977b297f5d5359 100644
> > --- a/drivers/gpu/drm/drm_modes.c
> > +++ b/drivers/gpu/drm/drm_modes.c
> > @@ -1623,6 +1623,40 @@ bool drm_mode_equal_no_clocks_no_stereo(const struct drm_display_mode *mode1,
> > }
> > EXPORT_SYMBOL(drm_mode_equal_no_clocks_no_stereo);
> >
> > +/**
> > + * drm_mode_validate_mode
> > + * @mode: mode to check
> > + * @rounded_rate: output pixel clock
> > + *
> > + * VESA DMT defines a tolerance of 0.5% on the pixel clock, while the
> > + * CVT spec reuses that tolerance in its examples, so it looks to be a
> > + * good default tolerance for the EDID-based modes. Define it to 5 per
> > + * mille to avoid floating point operations.
> > + *
> > + * Returns:
> > + * The mode status
> > + */
> > +enum drm_mode_status drm_mode_validate_mode(const struct drm_display_mode *mode,
> > + unsigned long long rounded_rate)
> > +{
> > + enum drm_mode_status status;
> > + unsigned long long rate = mode->clock * 1000;
> > + unsigned long long lowest, highest;
> > +
> > + lowest = rate * (1000 - 5);
> > + do_div(lowest, 1000);
> > + if (rounded_rate < lowest)
> > + return MODE_CLOCK_LOW;
> > +
> > + highest = rate * (1000 + 5);
> > + do_div(highest, 1000);
> > + if (rounded_rate > highest)
> > + return MODE_CLOCK_HIGH;
> > +
> > + return MODE_OK;
> > +}
> > +EXPORT_SYMBOL(drm_mode_validate_mode);
>
> Thanks a lot for doing that!
>
> I wonder about the naming though (and prototype). I doesn't really
> validates a mode, but rather makes sure that a given rate is a good
> approximation of a pixel clock. So maybe something like
> drm_mode_check_pixel_clock?
Naming is hard :) I will use drm_mode_check_pixel_clock() for V2.
Would it make sense to have the pixel clock requirement as a input
parameter? For HDMI it is 0.5% and in my case the LVDS panel 10%.
enum drm_mode_status drm_mode_validate_mode(const struct drm_display_mode *mode,
unsigned long long rounded_rate, unsigned tolerance)
?
And maybe a drm_mode_validate_mode_hdmi() with the default tolerance of
.5%?
>
> We probably need some kunit tests here too.
Good idea, will be my first :)
/Sean
