Re: [PATCH 4/8] drm/vc4: hdmi: Check and warn if we can't reach 4kp60 frequencies

Hi Dave,

Thanks for your review

On Thu, Feb 25, 2021 at 04:38:37PM +0000, Dave Stevenson wrote:

On Thu, 25 Feb 2021 at 15:59, Maxime Ripard maxime@cerno.tech wrote:

...

In order to reach the frequencies needed to output at 594MHz, the firmware needs to be configured with the appropriate parameters in the config.txt file (enable_hdmi_4kp60 and force_turbo).

force_turbo isn't the right way to go about this as it permanently bumps all the clocks up, even if running the display at VGA.

so enable_hdmi_4kp60 is enough?

...

Let's detect it at bind time, warn the user if we can't, and filter out the relevant modes.

Signed-off-by: Maxime Ripard maxime@cerno.tech

drivers/gpu/drm/vc4/vc4_hdmi.c | 17 +++++++++++++++++ drivers/gpu/drm/vc4/vc4_hdmi.h | 8 ++++++++ 2 files changed, 25 insertions(+)

diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c index b5bc742993a4..f05f6da286f7 100644 --- a/drivers/gpu/drm/vc4/vc4_hdmi.c +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c @@ -953,6 +953,9 @@ static int vc4_hdmi_encoder_atomic_check(struct drm_encoder *encoder, if (pixel_rate > vc4_hdmi->variant->max_pixel_clock) return -EINVAL;

•   if (vc4_hdmi->disable_4kp60 && (pixel_rate > HDMI_14_MAX_TMDS_CLK))
  

•           return -EINVAL;
  

•   vc4_state->pixel_rate = pixel_rate;
  
    return 0;
  

@@ -972,6 +975,9 @@ vc4_hdmi_encoder_mode_valid(struct drm_encoder *encoder, if ((mode->clock * 1000) > vc4_hdmi->variant->max_pixel_clock) return MODE_CLOCK_HIGH;

•   if (vc4_hdmi->disable_4kp60 && ((mode->clock * 1000) > HDMI_14_MAX_TMDS_CLK))
  

•           return MODE_CLOCK_HIGH;
  

•   return MODE_OK;
  

}

@@ -1986,6 +1992,17 @@ static int vc4_hdmi_bind(struct device *dev, struct device *master, void *data) vc4_hdmi->disable_wifi_frequencies = of_property_read_bool(dev->of_node, "wifi-2.4ghz-coexistence");

•   if (variant->max_pixel_clock == 600000000) {
  

•           struct vc4_dev *vc4 = to_vc4_dev(drm);
  

•           long max_rate = clk_get_max_rate(vc4->hvs->core_clk);
  

•           if (max_rate < 550000000) {
  

•                   drm_warn(drm, "The core clock cannot reach frequencies high enough to support 4k @ 60Hz.");
  

•                   drm_warn(drm, "Please change your config.txt file to add hdmi_enable_4kp60 and force_turbo");
  

Do we really want to warn in bind? Again you could have a VGA resolution monitor attached but that would trigger this warning. Can we warn (once) on processing the mode list and filtering out a clk

...

HDMI_14_MAX_TMDS_CLK mode instead?

That's a good idea indeed, I'll rework the patch to do that

Thanks! Maxime