DRI on radeon 9500 using too wide memory bus?

[Tijl Coosemans]

On Thursday 13 March 2008 22:45:35 Reid Linnemann wrote:
> Written by Reid Linnemann on 03/13/08 00:58>>
>> I've had DRI running on a radeon 9500 for a while now, and at some
>> point in time tracking 6-STABLE and continuing now on 7-STABLE I've
>> started seeing rendering artifacts in gl in the form of a
>> cross-hatch pattern of pixels that don't get filled. At first I
>> figured the card was failing, but I remembered a fact about the 9500
>> that made me doublethink that.
>> 
>> The radeon 9500 is an r300 chipset, and differs from the 9700 only
>> in the width of the memory bus (128 bit vs 256 bit) and possibly
>> clock speed. If memory serves, the chip itself had the capacity to
>> address 256 bits, but most 9500s just went out the door with 128 bit
>> memory. I remember at one point in time trying out a hack to the
>> 9500 driver that enabled the 256 bit bus to see if I had a rebadged
>> 9700, and had similar artifacts.
>> 
>> So I decided to peruse my X logs, and sure enough I see:
>> (--) RADEON(0): Mapped VideoRAM: 131072 kByte (256 bit DDR SDRAM)
>> 
>> Is it possible that the radeon driver is using the 256 bus? Is there
>> a way to force it to use a 128 bit bus? Has anyone else seen this?
> 
> On further investigation, I tried forcing the driver to switch to a
> 128 bit bus by setting the R300_MEM_NUM_CHANNELS_MASK bits on
> RADEON_MEM_CNTL to 0x1, but the problem did not go away.
> 
> I'll try describing it a little better.. only with gl acceleration,
> the entire gl context appears to have criss-crossing lines 4 pixels
> wide that are randomly filled correctly or black, so that they form
> roughly a chain link fence pattern of trash on the gl context. Anyone
> have an idea?

I can't help you with this, but I'm thinking you'll have a higher
chance getting an answer on some DRI/DRM mailinglist. You could also
ask the port maintainers (x11@). Some of them are also active
developers on DRI, and the r300 driver, or at least used to be in the
past.