radeon: allow the user to set a maximum HDMI pixel clock (in MHz) by a kernel parameter
Submitted by Elmar Stellnberger
Assigned to Elmar Stellnberger
Description
As far as I have seen radeon sets the pixel clock (in MHz) for the HDMI/DVI output to a value as recommended by the firmware, only. Since kernel 4.5.0 the nouveau driver has a kernel parameter called hdmimhz to override this setting by hand: As far as I could test it the results I get that way are just wonderful (see for Bug 93405).
The situation with my '4K ready' XFX Radeon R5 230 card is similar than it was with the nouveau driver before kernel 4.5.0: The promised 3840x2160@30 mode is not offered by default and when I try to set this mode manually the screen remains black (no signal). It was exactly like this with my Nv. Geforce 9600M GT until the hdmimhz kernel parameter appeared. Since then it works even better than officially specified by Nvidia with nouveau (nobody would have believed that).
Why isn`t there a similar parameter for radeon?
kernel version: 4.5.0-rc1-ARCH #2 SMP PREEMPT
radeon driver (xf86-video-ati/arch): 1:7.6.1-1