[PATCH 2/4] drm/radeon: convert fence to uint64_t

Jerome Glisse j.glisse at gmail.com
Thu May 3 08:56:41 PDT 2012

On Thu, May 3, 2012 at 7:39 AM, Christian König <deathsimple at vodafone.de> wrote:
> On 03.05.2012 09:21, Michel Dänzer wrote:
>> On Mit, 2012-05-02 at 16:20 -0400, j.glisse at gmail.com wrote:
>>> From: Jerome Glisse<jglisse at redhat.com>
>>> This convert fence to use uint64_t sequence number intention is
>>> to use the fact that uin64_t is big enough that we don't need to
>>> care about wrap around.
>>> Tested with and without writeback using 0xFFFFF000 as initial
>>> fence sequence and thus allowing to test the wrap around from
>>> 32bits to 64bits.
>>> Signed-off-by: Jerome Glisse<jglisse at redhat.com>
>> [...]
>>> diff --git a/drivers/gpu/drm/radeon/radeon_fence.c
>>> b/drivers/gpu/drm/radeon/radeon_fence.c
>>> index 7733429..6da1535 100644
>>> --- a/drivers/gpu/drm/radeon/radeon_fence.c
>>> +++ b/drivers/gpu/drm/radeon/radeon_fence.c
>>> @@ -386,9 +388,9 @@ int radeon_fence_driver_start_ring(struct
>>> radeon_device *rdev, int ring)
>>>                        rdev->fence_drv[ring].scratch_reg -
>>>                        rdev->scratch.reg_base;
>>>        }
>>> -       rdev->fence_drv[ring].cpu_addr =rdev->wb.wb[index/4];
>>> +       rdev->fence_drv[ring].cpu_addr =u64*)&rdev->wb.wb[index/4];
>> Might want to ensure cpu_addr is 64 bit aligned, or there might be
>> trouble on some architectures.
>> With this change, Cayman cards will already use six scratch registers
>> for the rings. It won't be possible to extend this scheme for even one
>> additional ring, will it?
> That won't work anyway, since not all rings can deal with 64 bit fences, so
> we need to still use 32 bit signaling and extend them to 64 bit while
> processing the fence value.
> Already working on that.
> Christian.

This patch is fine with ring that can't emit directly 64bits, all you
have to do is fix the emit_fence callback to properly handle it and
then you have to fix the radeon_fence_read which can be move to a ring
specific callback. Anyway point is that patchset works and is fine on
current set of ring we have and it can work as easily for ring without
easy 64bits value emitting. So please explain further why those patch
can't work because as i just explained i don't see why.

I have updated some v2 version of those patchset to handle the cayman
and newer possibly running out of scratch reg and i also fix the
alignment issue to be 64bits


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