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SubjectRe: [PATCH] drm/vc4: Fix HDMI mode validation
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Am 26.03.20 um 13:20 schrieb Nicolas Saenz Julienne:
> Current mode validation impedes setting up some video modes which should
> be supported otherwise. Namely 1920x1200@60Hz.
>
> Fix this by lowering the minimum HDMI state machine clock to pixel clock
> ratio allowed.
>
> Fixes: 32e823c63e90 ("drm/vc4: Reject HDMI modes with too high of clocks")
> Reported-by: Stefan Wahren <stefan.wahren@i2se.com>
> Suggested-by: Dave Stevenson <dave.stevenson@raspberrypi.com>
> Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
> ---
> drivers/gpu/drm/vc4/vc4_hdmi.c | 20 ++++++++++++++++----
> 1 file changed, 16 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c
> index cea18dc15f77..340719238753 100644
> --- a/drivers/gpu/drm/vc4/vc4_hdmi.c
> +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c
> @@ -681,11 +681,23 @@ static enum drm_mode_status
> vc4_hdmi_encoder_mode_valid(struct drm_encoder *crtc,
> const struct drm_display_mode *mode)
> {
> - /* HSM clock must be 108% of the pixel clock. Additionally,
> - * the AXI clock needs to be at least 25% of pixel clock, but
> - * HSM ends up being the limiting factor.
> + /*
> + * As stated in RPi's vc4 firmware "HDMI state machine (HSM) clock must
> + * be faster than pixel clock, infinitesimally faster, tested in
> + * simulation. Otherwise, exact value is unimportant for HDMI
> + * operation." This conflicts with bcm2835's vc4 documentation, which
> + * states HSM's clock has to be at least 108% of the pixel clock.
> + *
> + * Real life tests reveal that vc4's firmware statement holds up, and
> + * users are able to use pixel clocks closer to HSM's, namely for
> + * 1920x1200@60Hz. So it was decided to have leave a 1% margin between
> + * both clocks. Which, for RPi0-3 implies a maximum pixel clock of

s/RPi0-3/bcm2835/ ?

Beside this nit:

Tested-by: Stefan Wahren <stefan.wahre@i2se.com>

Thanks


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