graphics on G4

[Nathan Whitehorn]

Justin Hibbits wrote:
> On Fri, Mar 06, 2009 at 07:06:26AM -0500, Justin Hibbits wrote:
>>>>> Did you ever discover whether writing to random bits of the framebuffer 
>>>>> without ever having run X also causes this problem?
>>>>> -Nathan
>>>> Yes, I did perform that test, and it does cause the problem as well.  For me it
>>>> hangs when starting a new process some time later, so can be tested somewhat
>>>> easily by performing a buildworld after doing the graphics test.
>>> My card, at least, has a framebuffer BAR that is 128 MB long, but only 
>>> actually has 32 MB of graphics RAM. Writing anything to that 32 MB does 
>>> not cause problems, but of course writing beyond that kills the machine, 
>>> since that memory region does not actually exist. Is this true for yours 
>>>   as well?
>>> -Nathan
>> My card has 256MB of graphics RAM, and according to dmesg allocates that size
>> block, plus 64k in the 256MB region before it.  I haven't yet tested what
>> address byte actually causes the crash, but that can be determined relatively
>> easily.  What I'm guessing, though, is writing to anything past (end - 32k) will
>> cause the crash.  I'll see if I can test this weekend.
>>
>> So, short answer to your question: it's not quite true for me, because it
>> happens when I write to what should be inside graphics RAM.
>>
>> - Justin
> 
> Nathan-
> 
> Attached is a simple program I wrote that just writes a straight line down the
> first column of the framebuffer.  It reliably kills my system while running a
> 'make buildworld' within a few minutes of running this program.
> 
> (Possibly) Relevant Details:
> 
> ATI Radeon 9600PRO, 256MB edition.
> 1280x1024x8 framebuffer
> 1.25GiB RAM
> 
> - Justin
> 

Thanks for the test. It looks like you've exposed a bug in how we mmap() 
physical memory. It seems that if you try to write to the last page of 
any mmap()ed physmem region, you get a panic in UMA. Using write(), on 
the other hand, works just fine.
-Nathan