[PATCH] agp: Enable all supported rates for graphic cards

[Tormod Volden]

On Sun, Nov 6, 2011 at 4:37 PM, Corbin Simpson
<mostawesomedude at gmail.com> wrote:
> Trusting the spec worries me; could this break anybody?

It will allow the user to override possibly safer default settings. If
a user has specified, say, 2x in his xorg.conf and this was not
honored because the card only reported 4x, this patch would finally
give him the 2x he is asking for. If 2x turns out to not work, he will
suddenly have problems. But the solution would be to fix his
xorg.conf. Up till now he might be thinking 2x works fine, while he
was actually getting another rate.

Generally, the default rate is defined by the DDX and the patch does
not change these policies. However, with the patch we may actually
apply the default value, instead of an undefined "0x" (i.e. the case
when the DDX sets 1x or 2x by default, but the card says only 4x). The
spec (I have checked section 6.1.10) does not say anything about
writing a zero rate, and I don't know what the silicon does. I don't
know of any way to read out the resulting speed. Is there any simple
agp benchmarking tools?

Of course, it would be good if more people who currently see "0x" in
dmesg would try this patch.

Note that Dave Jones did the same for bridges in
28af24bb8470c7d0573b703a2955548b73a6c066 to get rid of "0x" cases.

>
> Is there any reason to use the not-so-magic numbers instead of the named
> constants?

I followed the style of the surrounding code. I can follow up with a
patch using named constants everywhere if that would be desired.

Thanks for looking at it!
Tormod


>
> Sending from a mobile, pardon my terseness. ~ C.
>
> On Nov 6, 2011 7:03 AM, "Tormod Volden" <lists.tormod at gmail.com> wrote:
>>
>> From: Tormod Volden <debian.tormod at gmail.com>
>>
>> Some cards report that they support only 4x, in which case they
>> should support 2x and 1x as well, according to the AGP spec.
>>
>> Otherwise a requested 1x or 2x rate will result in 0 being set:
>>
>> agpgart-via 0000:00:00.0: putting AGP V2 device into 0x mode
>>
>> For instance ProSavage KN133 [5333:8d02] only reports 4x.
>>
>> Signed-off-by: Tormod Volden <debian.tormod at gmail.com>
>> ---
>>  drivers/char/agp/generic.c |   18 ++++++++++++++++++
>>  1 files changed, 18 insertions(+), 0 deletions(-)
>>
>> diff --git a/drivers/char/agp/generic.c b/drivers/char/agp/generic.c
>> index b072648..c5d04e5 100644
>> --- a/drivers/char/agp/generic.c
>> +++ b/drivers/char/agp/generic.c
>> @@ -526,6 +526,24 @@ static void agp_v2_parse_one(u32 *requested_mode, u32
>> *bridge_agpstat, u32 *vga_
>>                break;
>>        }
>>
>> +       /* Some graphic cards report they only support 4x, however the AGP
>> 2.0 spec
>> +        * (section 4.1.1) says components must support the lower speeds
>> as well.
>> +        */
>> +       switch (*vga_agpstat & 7) {
>> +       case 4:
>> +               *vga_agpstat |= (AGPSTAT2_2X | AGPSTAT2_1X);
>> +               printk(KERN_INFO PFX "Graphics card claims to only support
>> x4 rate. "
>> +                       "Fixing up support for x2 & x1\n");
>> +               break;
>> +       case 2:
>> +               *vga_agpstat |= AGPSTAT2_1X;
>> +               printk(KERN_INFO PFX "Graphics card claims to only support
>> x2 rate. "
>> +                       "Fixing up support for x1\n");
>> +               break;
>> +       default:
>> +               break;
>> +       }
>> +
>>        /* Check the speed bits make sense. Only one should be set. */
>>        tmp = *requested_mode & 7;
>>        switch (tmp) {
>> --
>> 1.7.5.4
>>
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>