On Tue, Mar 02, 2021 at 04:15:06PM +0300, Dmitry Osipenko wrote:
RGB output doesn't allow to change parent clock rate of the display and PCLK rate is set to 0Hz in this case. The tegra_dc_commit_state() shall not set the display clock to 0Hz since this change propagates to the parent clock. The DISP clock is defined as a NODIV clock by the tegra-clk driver and all NODIV clocks use the CLK_SET_RATE_PARENT flag.
This bug stayed unnoticed because by default PLLP is used as the parent clock for the display controller and PLLP silently skips the erroneous 0Hz rate changes because it always has active child clocks that don't permit rate changes. The PLLP isn't acceptable for some devices that we want to upstream (like Samsung Galaxy Tab and ASUS TF700T) due to a display panel clock rate requirements that can't be fulfilled by using PLLP and then the bug pops up in this case since parent clock is set to 0Hz, killing the display output.
Don't touch DC clock if pclk=0 in order to fix the problem.
Signed-off-by: Dmitry Osipenko digetx@gmail.com
drivers/gpu/drm/tegra/dc.c | 10 +++++----- 1 file changed, 5 insertions(+), 5 deletions(-)
Applied, thanks.
Thierry