LCM flicker

[Cesar Eduardo Barros]

Werner Almesberger escreveu:
> Andy Green wrote:
>> Maybe the GTA01 batch of LCMs are
>> themselves different from the ones we currently use.
> 
> I connected my GTA01Bv4 LCM to a GTA02v4, and it showed all the same
> flicker.
> 
>> Maybe this is because the GTA01 issued the video at a higher
>> frame rate and the flicker is less visible.
> 
> That is the case, yes. I just measured that HSYNC on GTA02 is 40.9kHz,
> while on GTA01 it's 55.4kHz (!)

With GTA01, it does flicker when using cpufreq on some frequencies.

The problem on GTA01 is that the base frequency can be either HCLK/4 or 
HCLK/2, and neither gets near the ideal set of values. The kernel will 
always try to stay below the specified "pixclock" parameter; but, while 
that is set on mach-gta01.c to 40000, the value actually used after the 
rouding (on the default core frequency) corresponds to a pixclock of 30075.

To reduce the issue, I changed the parameter on mach-gta01.c to 35000 
instead of 40000 on my cpufreq tree (the frequencies which flicker the 
most are the ones where the effective value is near 40000). I also made 
cpufreq stop using the slower frequencies (ones which would want to use 
HCLK instead of HCLK/2, which is not possible) when the LCD controller 
is enabled (and, unfortunately, it currently never gets disabled; the 
screen only gets blanked). Both changes combined make the effective 
pixclock range 17500-35000 instead of 20000-40000. However, that's only 
a workaround (the flicker is still there, only reduced, and you can 
still notice when "ondemand" is giving you a slower frequency).

-- 
Cesar Eduardo Barros
cesarb at cesarb.net
cesar.barros at gmail.com