[prev in list] [next in list] [prev in thread] [next in thread] 

List:       freedesktop-xorg
Subject:    Re: pci rework not quite ready yet?
From:       Josh Triplett <josh () freedesktop ! org>
Date:       2007-09-30 4:13:08
Message-ID: 46FF2254.3060402 () freedesktop ! org
[Download RAW message or body]

[Attachment #2 (multipart/signed)]


Jesse Barnes wrote:
> On Wednesday, August 29, 2007 9:10 am Keith Packard wrote:
>> On Wed, 2007-08-29 at 08:11 -0700, Jesse Barnes wrote:
>>> I'd be much happier if we just got away from using bus
>>> addresses entirely.  There's really no way we can use them reliably
>>> short of growing sophisticated bus drivers in the X server...
>> I disagree -- all bus addresses for a single card live in a single
>> address space, and the driver must use many of them while programming
>> various operations. In particular, if you want to split a single BAR
>> into multiple 'regions' (as we do on Intel cards when mapping the
>> GTT), then you must talk about bus addresses instead of trying to
>> hide entirely behind a BAR abstraction.
>>
>> It's also far easier to store just the bus address in the driver than
>> to track both BAR index and offset. Given that you must often program
>> the card with bus addresses, it doesn't make sense to make the driver
>> constantly refer back to the pci BAR tables unless you think those
>> are going to change.
> 
> Yeah, I guess my main concern is how buggy some of the core X usage of 
> bus addresses has been.  As long as we can avoid that by making clear 
> the difference between bus, CPU physical, GTT virtual, and process 
> virtual I'll be happy.

To help keep address spaces straight, you might consider using the
address_space attribute of Sparse, like the Linux kernel does:

#ifdef __CHECKER__
#define __physical __attribute__((address_space(1)))
#define __gtt_virtual __attribute__((address_space(2)))
...
#else
#define __physical
...
#endif
...
extern void needs_a_gtt_virtual(void __gtt_virtual *);
...
void has_a_physical(void __physical *foo)
{
   needs_a_gtt_virtual(foo); /* Will warn */
...

You can also throw in the attribute "noderef" as well, to prevent
dereferencing foo.

- Josh Triplett


["signature.asc" (application/pgp-signature)]

_______________________________________________
xorg mailing list
xorg@lists.freedesktop.org
http://lists.freedesktop.org/mailman/listinfo/xorg

[prev in list] [next in list] [prev in thread] [next in thread]