ATI Drivers report bogus dot_clock to xvidtune

[Alex Deucher]

On 28 Mar 2006 15:55:47 -0500, Greg Stark <gsstark at mit.edu> wrote:
> "Alex Deucher" <alexdeucher at gmail.com> writes:
>
> > On 3/28/06, Roland Scheidegger <rscheidegger_lists at hispeed.ch> wrote:
> >
> > I also don't see how the dotclock would be of any use for vblank, but
> > I suspect you are seeing a limitation of mergedfb.  Mergedfb is
> > basically a hack to treat 2 crtcs as a single screen.  since you have
> > two crtcs with different timings there's no way to know which dotclock
> > or refresh rate, etc. is relevant (since they both are). Hence you end
> > up with some weirdness for certain fields.  Disable mergedfb if you
> > want relevant numbers for those fields.
>
> Yes I expect it's caused by mergedfb. I suspect what's happening is that it's
> calculating the dot clock based on the refresh rate and the combined desktop
> size. And it's overflowing somewhere. Though I'm stumped where since it ought
> not be overflowing a 32-bit integer. Perhaps it's doing some of the math in
> 16-bit integers?

IIRC, it doesn't do anything special so you get random garbage.

>
> > > This looks like a driver bug. I have no idea though what driver you're
> > > talking about, there is no such thing as a ati driver (well there is
> > > technically, a driver wrapper which is called ati, but it doesn't do
> > > anyhting itself). So is this mach64? rage128? radeon? fglrx (take it to
> > > ati in that case)?
> > > If that's radeon are you using mergedfb? It works just fine for me
> > > without mergedfb.
> > > That said, I don't know why mythtv would need the pixel clock to sync to
> > > vblank, I'd think it's a pretty useless number for that.
>
> It's radeon. The card is a radeon 9600 (RV350). And yes I'm using mergedfb.
>
> I would actually rather not be using mergedfb but I haven't figured out how to
> configure it not to.

Option "mergedfb" "false"

in the device section of your config.

Alex

>
> It calculates the refresh rate and then I guess it tries to lock the output
> frame rate to the refresh rate. Ie, there's no need to output frames faster
> than the refresh rate.
>
> --
> greg
>
>