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drm/vc4: Fix HDMI mode validation

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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: 32e823c63e ("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>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20200326122001.22215-1-nsaenzjulienne@suse.de
This commit is contained in:
Nicolas Saenz Julienne 2020-03-26 13:20:01 +01:00 committed by Maxime Ripard
parent a65a97b486
commit b1e7396a1d
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GPG Key ID: E3EF0D6F671851C5
1 changed files with 16 additions and 4 deletions
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20
drivers/gpu/drm/vc4/vc4_hdmi.c
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@ -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
* 162MHz.
*
* Additionally, the AXI clock needs to be at least 25% of
* pixel clock, but HSM ends up being the limiting factor.
*/
if (mode->clock > HSM_CLOCK_FREQ / (1000 * 108 / 100))
if (mode->clock > HSM_CLOCK_FREQ / (1000 * 101 / 100))
return MODE_CLOCK_HIGH;
return MODE_OK;