Re: [PATCH 04/17] dma-fence: Allow wait_any_timeout for all fences

[Daniel Vetter]

On Sun, Apr 29, 2018 at 09:11:31AM +0200, Christian König wrote:
> Am 27.04.2018 um 08:17 schrieb Daniel Vetter:
> > When this was introduced in
> > 
> > commit a519435a96597d8cd96123246fea4ae5a6c90b02
> > Author: Christian König 
> > Date:   Tue Oct 20 16:34:16 2015 +0200
> > 
> >  dma-buf/fence: add fence_wait_any_timeout function v2
> > 
> > there was a restriction added that this only works if the dma-fence
> > uses the dma_fence_default_wait hook. Which works for amdgpu, which is
> > the only caller. Well, until you share some buffers with e.g. i915,
> > then you get an -EINVAL.
> > 
> > But there's really no reason for this, because all drivers must
> > support callbacks. The special ->wait hook is only as an optimization;
> > if the driver needs to create a worker thread for an active callback,
> > then it can avoid to do that if it knows that there's a process
> > context available already. So ->wait is just an optimization, just
> > using the logic in dma_fence_default_wait() should work for all
> > drivers.
> > 
> > Let's remove this restriction.
> 
> Mhm, that was intentional introduced because for radeon that is not only an
> optimization, but mandatory for correct operation.
> 
> On the other hand radeon isn't using this function, so it should be fine as
> long as the Intel driver can live with it.

Well dma-buf already requires that dma_fence_add_callback works correctly.
And so do various users of it as soon as you engage in a bit of buffer
sharing. I guess whomever cares about buffer sharing with radeon gets to
fix this (you need to spawn a kthread or whatever in ->enable_signaling
which does the same work as your optimized ->wait callback).

But yeah, I'm definitely not making things work with this series, just a
bit more obvious that there's a problem already.
-Daniel

> 
> Christian.
> 
> > 
> > Signed-off-by: Daniel Vetter 
> > Cc: Sumit Semwal 
> > Cc: Gustavo Padovan 
> > Cc: linux-media@vger.kernel.org
> > Cc: linaro-mm-...@lists.linaro.org
> > Cc: Christian König 
> > Cc: Alex Deucher 
> > ---
> >   drivers/dma-buf/dma-fence.c | 5 -
> >   1 file changed, 5 deletions(-)
> > 
> > diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
> > index 7b5b40d6b70e..59049375bd19 100644
> > --- a/drivers/dma-buf/dma-fence.c
> > +++ b/drivers/dma-buf/dma-fence.c
> > @@ -503,11 +503,6 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, 
> > uint32_t count,
> > for (i = 0; i < count; ++i) {
> > struct dma_fence *fence = fences[i];
> > -   if (fence->ops->wait != dma_fence_default_wait) {
> > -   ret = -EINVAL;
> > -   goto fence_rm_cb;
> > -   }
> > -
> > cb[i].task = current;
> > if (dma_fence_add_callback(fence, [i].base,
> >dma_fence_default_wait_cb)) {
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch

Re: [PATCH 04/17] dma-fence: Allow wait_any_timeout for all fences

[Christian König]

Am 27.04.2018 um 08:17 schrieb Daniel Vetter:

When this was introduced in

commit a519435a96597d8cd96123246fea4ae5a6c90b02
Author: Christian König 
Date:   Tue Oct 20 16:34:16 2015 +0200

 dma-buf/fence: add fence_wait_any_timeout function v2

there was a restriction added that this only works if the dma-fence
uses the dma_fence_default_wait hook. Which works for amdgpu, which is
the only caller. Well, until you share some buffers with e.g. i915,
then you get an -EINVAL.

But there's really no reason for this, because all drivers must
support callbacks. The special ->wait hook is only as an optimization;
if the driver needs to create a worker thread for an active callback,
then it can avoid to do that if it knows that there's a process
context available already. So ->wait is just an optimization, just
using the logic in dma_fence_default_wait() should work for all
drivers.

Let's remove this restriction.


Mhm, that was intentional introduced because for radeon that is not only 
an optimization, but mandatory for correct operation.


On the other hand radeon isn't using this function, so it should be fine 
as long as the Intel driver can live with it.


Christian.



Signed-off-by: Daniel Vetter 
Cc: Sumit Semwal 
Cc: Gustavo Padovan 
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-...@lists.linaro.org
Cc: Christian König 
Cc: Alex Deucher 
---
  drivers/dma-buf/dma-fence.c | 5 -
  1 file changed, 5 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 7b5b40d6b70e..59049375bd19 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -503,11 +503,6 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, 
uint32_t count,
for (i = 0; i < count; ++i) {
struct dma_fence *fence = fences[i];
  
-		if (fence->ops->wait != dma_fence_default_wait) {

-   ret = -EINVAL;
-   goto fence_rm_cb;
-   }
-
cb[i].task = current;
if (dma_fence_add_callback(fence, [i].base,
   dma_fence_default_wait_cb)) {

[PATCH 04/17] dma-fence: Allow wait_any_timeout for all fences

[Daniel Vetter]

When this was introduced in

commit a519435a96597d8cd96123246fea4ae5a6c90b02
Author: Christian König 
Date:   Tue Oct 20 16:34:16 2015 +0200

dma-buf/fence: add fence_wait_any_timeout function v2

there was a restriction added that this only works if the dma-fence
uses the dma_fence_default_wait hook. Which works for amdgpu, which is
the only caller. Well, until you share some buffers with e.g. i915,
then you get an -EINVAL.

But there's really no reason for this, because all drivers must
support callbacks. The special ->wait hook is only as an optimization;
if the driver needs to create a worker thread for an active callback,
then it can avoid to do that if it knows that there's a process
context available already. So ->wait is just an optimization, just
using the logic in dma_fence_default_wait() should work for all
drivers.

Let's remove this restriction.

Signed-off-by: Daniel Vetter 
Cc: Sumit Semwal 
Cc: Gustavo Padovan 
Cc: linux-media@vger.kernel.org
Cc: linaro-mm-...@lists.linaro.org
Cc: Christian König 
Cc: Alex Deucher 
---
 drivers/dma-buf/dma-fence.c | 5 -
 1 file changed, 5 deletions(-)

diff --git a/drivers/dma-buf/dma-fence.c b/drivers/dma-buf/dma-fence.c
index 7b5b40d6b70e..59049375bd19 100644
--- a/drivers/dma-buf/dma-fence.c
+++ b/drivers/dma-buf/dma-fence.c
@@ -503,11 +503,6 @@ dma_fence_wait_any_timeout(struct dma_fence **fences, 
uint32_t count,
for (i = 0; i < count; ++i) {
struct dma_fence *fence = fences[i];
 
-   if (fence->ops->wait != dma_fence_default_wait) {
-   ret = -EINVAL;
-   goto fence_rm_cb;
-   }
-
cb[i].task = current;
if (dma_fence_add_callback(fence, [i].base,
   dma_fence_default_wait_cb)) {
-- 
2.17.0