Re: [PATCH] radeonfb: (#2) Implement proper workarounds for PLL accesses

[Moritz Muehlenhoff <jmm@inutil.org>]

Benjamin Herrenschmidt wrote:
>> radeonfb_setcolreg: INPLL
>> radeonfb_setcolreg: OUTPLL
>> radeonfb_setcolreg: OUTPLL
>> ... last three lines repeated 63 times
>
> Hrm... the last (serie of 64 setcolreg) are probably X beeing extremely
> dumb, and calling the ioctl 64 times to set each palette entry instead
> of doing a single call for the whole palette...
>
> Anyway. Except for maybe the double set-par on switch from X to console,
> there isn't much more we can do here. We might be able to improve X but
> there is a significant lag between a fix done to X.org HEAD appears in
> any distro. The fact is, according to ATI, there is a HW bug on M6 taht
> can cause lockups of the chip, and this 5ms workaround is necessary to
> avoid it... 

But it's not specific to X11; I've applied the patch you posted and the
same symptoms occur for pure tty switching as well, the delay has decreased
a bit (it's hard to measure, but around a second), but it's still rather
annoying to work with.

Is it distinguishable which M6 models are buggy? I'm using my X31 for about
a year now and have probably made some tens of thousands of switches without
lockups, so presumably not all models cause lockups.

Cheers,
        Moritz
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