[PATCHv3 2/2] radeon: use max_bus_speed to activate gen2 speeds

[Dave Airlie]

>>
>> diff --git a/drivers/gpu/drm/radeon/evergreen.c b/drivers/gpu/drm/radeon/evergreen.c
>> index 305a657..3291f62 100644
>> --- a/drivers/gpu/drm/radeon/evergreen.c
>> +++ b/drivers/gpu/drm/radeon/evergreen.c
>> @@ -3855,8 +3855,7 @@ void evergreen_fini(struct radeon_device *rdev)
>>
>>  void evergreen_pcie_gen2_enable(struct radeon_device *rdev)
>>  {
>> -       u32 link_width_cntl, speed_cntl, mask;
>> -       int ret;
>> +       u32 link_width_cntl, speed_cntl;
>>
>>         if (radeon_pcie_gen2 == 0)
>>                 return;
>> @@ -3871,11 +3870,7 @@ void evergreen_pcie_gen2_enable(struct radeon_device *rdev)
>>         if (ASIC_IS_X2(rdev))
>>                 return;
>>
>> -       ret = drm_pcie_get_speed_cap_mask(rdev->ddev, &mask);
>> -       if (ret != 0)
>> -               return;
>> -
>> -       if (!(mask & DRM_PCIE_SPEED_50))
>> +       if (rdev->pdev->bus->max_bus_speed < PCIE_SPEED_5_0GT)
>
> For devices on a root bus, we previously dereferenced a NULL pointer
> in drm_pcie_get_speed_cap_mask() because pdev->bus->self is NULL on a
> root bus.  (I think this is the original problem you tripped over,
> Lucas.)
>
> These patches fix that problem.  On pseries, where the device *is* on
> a root bus, your patches set max_bus_speed so this will work as
> expected.  On most other systems, max_bus_speed for root buses will be
> PCI_SPEED_UNKNOWN (set in pci_alloc_bus() and never updated because
> most arches don't have code like the pseries code you're adding).
>
> PCI_SPEED_UNKNOWN = 0xff, so if we see another machine with a GPU on
> the root bus, we'll attempt to enable Gen2 on the device even though
> we have no idea what the bus will support.
>
> That's why I originally suggested skipping the Gen2 stuff if
> "max_bus_speed == PCI_SPEED_UNKNOWN".  I was just being conservative,
> thinking that it's better to have a functional but slow GPU rather
> than the unknown (to me) effects of enabling Gen2 on a link that might
> not support it.  But I'm fine with this being either way.
>
> It would be nice if we could get rid of drm_pcie_get_speed_cap_mask()
> altogether.  It is exported, but I have no idea of anybody else uses
> it.  Maybe it could at least be marked __deprecated now?
>
> I don't know who should take these patches.  They don't touch
> drivers/pci, but I'd be happy to push them, given the appropriate ACKs
> from DRM and powerpc folks.
>

Acked-by: Dave Airlie <airlied at redhat.com>

I'm happy to see these go via pci tree to avoid interdependent trees.

Dave.