[Xorg-driver-geode] Disable compression patch? huh?

[Warren Togami]

Jordan Crouse wrote:
> On 15/02/08 11:03 -0500, Warren Togami wrote:
>> Hi folks,
>>
>> I am now attempting to pull in the latest upstream drv-amd into Fedora.
>>
>> http://cvs.fedoraproject.org/viewcvs/devel/xorg-x11-drv-amd/
>> We have very old patches in our Fedora 8 driver.  I have confirmed with 
>> Dan Williams that two patches are no longer needed.
>>
>> http://cvs.fedoraproject.org/viewcvs/devel/xorg-x11-drv-amd/lx-disable-compression.patch?rev=1.1&view=log
>> But this patch we are uncertain.  Ajax recalls that it was framebuffer 
>> compression was definitely broken in some way in the past thus it was 
>> completely disabled in our driver.  Interestingly, he also mentions that 
>> "compression" actually uses more memory than without in this case.
> 
> Yes - compression doesn't mean what you think it means </princess_bride>
> 
> In this particular case, what is being compressed is the data traveling
> across the internal bus between the memory controller and the display
> controller.  In order to do this in the hardware, the pitch in the
> framebuffer needs to be a power of two; so in the case of the OLPC
> instead of a pitch of (1200x2=2400), the pitch would be 4096, which
> ended up expending very nearly 2 MB more of memory.
> 
> Compression is most useful for situations where this is a enormous 
> amount of traffic on the internal bus combined with high display
> resolutions - like, say streaming video from a PCI attached NIC in 720p
> resolution.  Most other people wouldn't use it, though they probably
> wouldn't notice or care if it was enabled.
> 
> I do remember some issues with compression in the past, but we've had
> it enabled by default in the driver for some time now, and I haven't
> heard any complaints.  Part of the reason why we patched it out in
> the Fedora driver was because we wanted it disabled for the memory
> hogging reason, and the OLPC guys preferred to have it disabled in the
> code rather then manually disabling it in the configuration file.
> 
> Jordan
> 

Thanks for the explanation.  Could we add a conditional upstream that 
turns off compression for OLPC hardware without disabling it by default 
for everyone else?

I'm removing this patch from Fedora now.

Warren Togami
wtogami at redhat.com