Hi Maxime On Fri, 2 Oct 2020 at 16:19, Maxime Ripard <maxime@xxxxxxxxxx> wrote: > > Hi Tim, > > On Thu, Oct 01, 2020 at 11:15:46AM +0100, Tim Gover wrote: > > hdmi_enable_4k60=1 causes the firmware to select 3.3 GHz for the PLLC > > VCO to support a core-frequency of 550 MHz which is the minimum > > frequency required by the HVS at 4Kp60. The side effect is that if the > > display clock requirements are lower than 4Kp60 then you will see > > different core frequencies selected by DVFS. > > > > If enable_uart=1 and the mini-uart is selected (default unless > > bluetooth is disabled) then the firmware will pin the core-frequency > > to either core_freq max (500 or 550). Although, I think there is a way > > of pinning it to a lower fixed frequency. > > > > The table in overclocking.md defines options for setting the maximum > > core frequency but unless core_freq_min is specified DVFS will > > automatically pick the lowest idle frequency required by the display > > resolution. > > I'm wondering if there's some way to detect this from Linux? I guess it > would be nice to be able to at least detect a broken config to warn / > prevent an user that their situation is not going to be reliable / work > really well (like if they have a 4k display without hdmi_enable_4kp60 > set, or the issue we're discussing here) The main filter in the firmware is the parameter hdmi_pixel_freq_limit. That can either be set manually from config.txt, or defaults appropriately based on hdmi_enable_4kp60. Under firmware_kms [1] I read back those values to use as a filter within crtc_mode_valid[2]. I can't think of a nice way of exposing that without the vc4 driver gaining a DT link to the firmware, and that starts to get ugly. Dave [1] https://github.com/raspberrypi/linux/blob/rpi-5.9.y/drivers/gpu/drm/vc4/vc4_firmware_kms.c#L1859 [2] https://github.com/raspberrypi/linux/blob/rpi-5.9.y/drivers/gpu/drm/vc4/vc4_firmware_kms.c#L1077 _______________________________________________ dri-devel mailing list dri-devel@xxxxxxxxxxxxxxxxxxxxx https://lists.freedesktop.org/mailman/listinfo/dri-devel
