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?
We probably need some kunit tests here too.
Maxime
Attachment:
signature.asc
Description: PGP signature
