Re: [Intel-gfx] [PATCH 15/15] RFC: drm/amdgpu: Implement a proper implicit fencing uapi

["Christian König" <christian.koenig@amd.com>]

Am 23.06.21 um 17:03 schrieb Daniel Vetter:
> On Wed, Jun 23, 2021 at 04:58:27PM +0200, Bas Nieuwenhuizen wrote:
>> On Wed, Jun 23, 2021 at 4:50 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>>> On Wed, Jun 23, 2021 at 4:02 PM Christian König
>>> <christian.koenig@amd.com> wrote:
>>>> Am 23.06.21 um 15:49 schrieb Daniel Vetter:
>>>>> On Wed, Jun 23, 2021 at 3:44 PM Christian König
>>>>> <christian.koenig@amd.com> wrote:
>>>>>> Am 23.06.21 um 15:38 schrieb Bas Nieuwenhuizen:
>>>>>>> On Wed, Jun 23, 2021 at 2:59 PM Christian König
>>>>>>> <christian.koenig@amd.com> wrote:
>>>>>>>> Am 23.06.21 um 14:18 schrieb Daniel Vetter:
>>>>>>>>> On Wed, Jun 23, 2021 at 11:45 AM Bas Nieuwenhuizen
>>>>>>>>> <bas@basnieuwenhuizen.nl> wrote:
>>>>>>>>>> On Tue, Jun 22, 2021 at 6:55 PM Daniel Vetter <daniel.vetter@ffwll.ch> wrote:
>>>>>>>>>>> WARNING: Absolutely untested beyond "gcc isn't dying in agony".
>>>>>>>>>>>
>>>>>>>>>>> Implicit fencing done properly needs to treat the implicit fencing
>>>>>>>>>>> slots like a funny kind of IPC mailbox. In other words it needs to be
>>>>>>>>>>> explicitly. This is the only way it will mesh well with explicit
>>>>>>>>>>> fencing userspace like vk, and it's also the bare minimum required to
>>>>>>>>>>> be able to manage anything else that wants to use the same buffer on
>>>>>>>>>>> multiple engines in parallel, and still be able to share it through
>>>>>>>>>>> implicit sync.
>>>>>>>>>>>
>>>>>>>>>>> amdgpu completely lacks such an uapi. Fix this.
>>>>>>>>>>>
>>>>>>>>>>> Luckily the concept of ignoring implicit fences exists already, and
>>>>>>>>>>> takes care of all the complexities of making sure that non-optional
>>>>>>>>>>> fences (like bo moves) are not ignored. This support was added in
>>>>>>>>>>>
>>>>>>>>>>> commit 177ae09b5d699a5ebd1cafcee78889db968abf54
>>>>>>>>>>> Author: Andres Rodriguez <andresx7@gmail.com>
>>>>>>>>>>> Date:   Fri Sep 15 20:44:06 2017 -0400
>>>>>>>>>>>
>>>>>>>>>>>         drm/amdgpu: introduce AMDGPU_GEM_CREATE_EXPLICIT_SYNC v2
>>>>>>>>>>>
>>>>>>>>>>> Unfortuantely it's the wrong semantics, because it's a bo flag and
>>>>>>>>>>> disables implicit sync on an allocated buffer completely.
>>>>>>>>>>>
>>>>>>>>>>> We _do_ want implicit sync, but control it explicitly. For this we
>>>>>>>>>>> need a flag on the drm_file, so that a given userspace (like vulkan)
>>>>>>>>>>> can manage the implicit sync slots explicitly. The other side of the
>>>>>>>>>>> pipeline (compositor, other process or just different stage in a media
>>>>>>>>>>> pipeline in the same process) can then either do the same, or fully
>>>>>>>>>>> participate in the implicit sync as implemented by the kernel by
>>>>>>>>>>> default.
>>>>>>>>>>>
>>>>>>>>>>> By building on the existing flag for buffers we avoid any issues with
>>>>>>>>>>> opening up additional security concerns - anything this new flag here
>>>>>>>>>>> allows is already.
>>>>>>>>>>>
>>>>>>>>>>> All drivers which supports this concept of a userspace-specific
>>>>>>>>>>> opt-out of implicit sync have a flag in their CS ioctl, but in reality
>>>>>>>>>>> that turned out to be a bit too inflexible. See the discussion below,
>>>>>>>>>>> let's try to do a bit better for amdgpu.
>>>>>>>>>>>
>>>>>>>>>>> This alone only allows us to completely avoid any stalls due to
>>>>>>>>>>> implicit sync, it does not yet allow us to use implicit sync as a
>>>>>>>>>>> strange form of IPC for sync_file.
>>>>>>>>>>>
>>>>>>>>>>> For that we need two more pieces:
>>>>>>>>>>>
>>>>>>>>>>> - a way to get the current implicit sync fences out of a buffer. Could
>>>>>>>>>>>       be done in a driver ioctl, but everyone needs this, and generally a
>>>>>>>>>>>       dma-buf is involved anyway to establish the sharing. So an ioctl on
>>>>>>>>>>>       the dma-buf makes a ton more sense:
>>>>>>>>>>>
>>>>>>>>>>>       https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fdri-devel%2F20210520190007.534046-4-jason%40jlekstrand.net%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C517f0d3467324e7ce05008d936581f60%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637600574408265873%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=gntXLzlrqPxYj4Q3mQflD3arT9ad40S9AqsvtOXV4nk%3D&amp;reserved=0
>>>>>>>>>>>
>>>>>>>>>>>       Current drivers in upstream solves this by having the opt-out flag
>>>>>>>>>>>       on their CS ioctl. This has the downside that very often the CS
>>>>>>>>>>>       which must actually stall for the implicit fence is run a while
>>>>>>>>>>>       after the implicit fence point was logically sampled per the api
>>>>>>>>>>>       spec (vk passes an explicit syncobj around for that afaiui), and so
>>>>>>>>>>>       results in oversync. Converting the implicit sync fences into a
>>>>>>>>>>>       snap-shot sync_file is actually accurate.
>>>>>>>>>>>
>>>>>>>>>>> - Simillar we need to be able to set the exclusive implicit fence.
>>>>>>>>>>>       Current drivers again do this with a CS ioctl flag, with again the
>>>>>>>>>>>       same problems that the time the CS happens additional dependencies
>>>>>>>>>>>       have been added. An explicit ioctl to only insert a sync_file (while
>>>>>>>>>>>       respecting the rules for how exclusive and shared fence slots must
>>>>>>>>>>>       be update in struct dma_resv) is much better. This is proposed here:
>>>>>>>>>>>
>>>>>>>>>>>       https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Fdri-devel%2F20210520190007.534046-5-jason%40jlekstrand.net%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C517f0d3467324e7ce05008d936581f60%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637600574408265873%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=YtqHT756jlt5NX7Ydr3Kk1UMTb98nQhlcOlrnr%2B48HE%3D&amp;reserved=0
>>>>>>>>>>>
>>>>>>>>>>> These three pieces together allow userspace to fully control implicit
>>>>>>>>>>> fencing and remove all unecessary stall points due to them.
>>>>>>>>>>>
>>>>>>>>>>> Well, as much as the implicit fencing model fundamentally allows:
>>>>>>>>>>> There is only one set of fences, you can only choose to sync against
>>>>>>>>>>> only writers (exclusive slot), or everyone. Hence suballocating
>>>>>>>>>>> multiple buffers or anything else like this is fundamentally not
>>>>>>>>>>> possible, and can only be fixed by a proper explicit fencing model.
>>>>>>>>>>>
>>>>>>>>>>> Aside from that caveat this model gets implicit fencing as closely to
>>>>>>>>>>> explicit fencing semantics as possible:
>>>>>>>>>>>
>>>>>>>>>>> On the actual implementation I opted for a simple setparam ioctl, no
>>>>>>>>>>> locking (just atomic reads/writes) for simplicity. There is a nice
>>>>>>>>>>> flag parameter in the VM ioctl which we could use, except:
>>>>>>>>>>> - it's not checked, so userspace likely passes garbage
>>>>>>>>>>> - there's already a comment that userspace _does_ pass garbage in the
>>>>>>>>>>>       priority field
>>>>>>>>>>> So yeah unfortunately this flag parameter for setting vm flags is
>>>>>>>>>>> useless, and we need to hack up a new one.
>>>>>>>>>>>
>>>>>>>>>>> v2: Explain why a new SETPARAM (Jason)
>>>>>>>>>>>
>>>>>>>>>>> v3: Bas noticed I forgot to hook up the dependency-side shortcut. We
>>>>>>>>>>> need both, or this doesn't do much.
>>>>>>>>>>>
>>>>>>>>>>> v4: Rebase over the amdgpu patch to always set the implicit sync
>>>>>>>>>>> fences.
>>>>>>>>>> So I think there is still a case missing in this implementation.
>>>>>>>>>> Consider these 3 cases
>>>>>>>>>>
>>>>>>>>>> (format: a->b: b waits on a. Yes, I know arrows are hard)
>>>>>>>>>>
>>>>>>>>>> explicit->explicit: This doesn't wait now, which is good
>>>>>>>>>> Implicit->explicit: This doesn't wait now, which is good
>>>>>>>>>> explicit->implicit : This still waits as the explicit submission still
>>>>>>>>>> adds shared fences and most things that set an exclusive fence for
>>>>>>>>>> implicit sync will hence wait on it.
>>>>>>>>>>
>>>>>>>>>> This is probably good enough for what radv needs now but also sounds
>>>>>>>>>> like a risk wrt baking in new uapi behavior that we don't want to be
>>>>>>>>>> the end result.
>>>>>>>>>>
>>>>>>>>>> Within AMDGPU this is probably solvable in two ways:
>>>>>>>>>>
>>>>>>>>>> 1) Downgrade AMDGPU_SYNC_NE_OWNER to AMDGPU_SYNC_EXPLICIT for shared fences.
>>>>>>>>> I'm not sure that works. I think the right fix is that radeonsi also
>>>>>>>>> switches to this model, with maybe a per-bo CS flag to set indicate
>>>>>>>>> write access, to cut down on the number of ioctls that are needed
>>>>>>>>> otherwise on shared buffers. This per-bo flag would essentially select
>>>>>>>>> between SYNC_NE_OWNER and SYNC_EXPLICIT on a per-buffer basis.
>>>>>>>> Yeah, but I'm still not entirely sure why that approach isn't sufficient?
>>>>>>>>
>>>>>>>> Problem with the per context or per vm flag is that you then don't get
>>>>>>>> any implicit synchronization any more when another process starts using
>>>>>>>> the buffer.
>>>>>>> That is exactly what I want for Vulkan :)
>>>>>> Yeah, but as far as I know this is not something we can do.
>>>>>>
>>>>>> See we have use cases like screen capture and debug which rely on that
>>>>>> behavior.
>>>>> They will keep working, if (and only if) the vulkan side sets the
>>>>> winsys fences correctly. Also, everything else in vulkan aside from
>>>>> winsys is explicitly not synced at all, you have to import drm syncobj
>>>>> timeline on the gl side.
>>>>>
>>>>>> The only thing we can do is to say on a per buffer flag that a buffer
>>>>>> should not participate in implicit sync at all.
>>>>> Nah, this doesn't work. Because it's not a global decision, is a local
>>>>> decision for the rendered. Vulkan wants to control implicit sync
>>>>> explicitly, and the kernel can't force more synchronization. If a
>>>>> buffer is shared as a winsys buffer between vulkan client and gl using
>>>>> compositor, then you _have_ to use implicit sync on it. But vk needs
>>>>> to set the fences directly (and if the app gets it wrong, you get
>>>>> misrendering, but that is the specified behavour of vulkan).
>>>> Yeah, but that's exactly what we tried to avoid.
>>>>
>>>> Mhm, when we attach the flag to the process/VM then this would break the
>>>> use case of VA-API and Vulkan in the same process.
>>>>
>>>> But I think if you attach the flag to the context that should indeed
>>>> work fine.
>>> Yeah that's a question I have, whether the drm_file is shared within
>>> one process among everything, or whether radeonsi/libva/vk each have
>>> their own. If each have their own drm_file, then we should be fine,
>>> otherwise we need to figure out another place to put this (worst case
>>> as a CS extension that vk just sets on every submit).
>> libdrm_amdgpu dedupes it all so we mostly end up with one drm_file per
>> process (modulo minigbm on chromeos and modulo a master fd).
>>
>> That said the current proposal is for the context right? And on the
>> context this should pretty much work? So I'm not sure why this is the
>> part we are discussing?
> It's on the fpriv->vm, so on the FD. I assumed vulkan at least would want
> to have it's private VM for this. And on the quick I didn't see any other
> way to create a VM than to have an FD of your own.

You can't have your own FD in libdrm_amdgpu userspace. We had a pretty 
hard design discussion about that already.

What you could do is to load your own copy of libdrm_amdgpu, but I won't 
recommend that.

Just putting the flag on the context instead of the VM is much cleaner 
as far as I can see anyway.

Christian.

> If there's something else that means "gpu context with it's own vm" then
> the flag would need to be moved there, pointers appreciated (but maybe
> someone with hw + userspace can do that quicker).
> -Daniel
>
>>> Also yes this risks that a vk app which was violationing the winsys
>>> spec will now break, which is why I think we should do this sooner
>>> than later. Otherwise the list of w/a we might need to apply in vk
>>> userspace will become very long :-( At least since this is purely
>>> opt-in from userspace, we only need to have the w/a list in userspace,
>>> where mesa has the infrastructure for that already.
>>> -Daniel
>>>
>>>> Christian.
>>>>
>>>>> -Daniel
>>>>>
>>>>>> Regards,
>>>>>> Christian.
>>>>>>
>>>>>>>>> The current amdgpu uapi just doesn't allow any other model without an
>>>>>>>>> explicit opt-in. So current implicit sync userspace just has to
>>>>>>>>> oversync, there's not much choice.
>>>>>>>>>
>>>>>>>>>> 2) Have an EXPLICIT fence owner that is used for explicit submissions
>>>>>>>>>> that is ignored by AMDGPU_SYNC_NE_OWNER.
>>>>>>>>>>
>>>>>>>>>> But this doesn't solve cross-driver interactions here.
>>>>>>>>> Yeah cross-driver is still entirely unsolved, because
>>>>>>>>> amdgpu_bo_explicit_sync() on the bo didn't solve that either.
>>>>>>>> Hui? You have lost me. Why is that still unsolved?
>>>>>>> The part we're trying to solve with this patch is Vulkan should not
>>>>>>> participate in any implicit sync at all wrt submissions (and then
>>>>>>> handle the implicit sync for WSI explicitly using the fence
>>>>>>> import/export stuff that Jason wrote). As long we add shared fences to
>>>>>>> the dma_resv we participate in implicit sync (at the level of an
>>>>>>> implicit sync read) still, at least from the perspective of later jobs
>>>>>>> waiting on these fences.
>>>>>>>
>>>>>>>> Regards,
>>>>>>>> Christian.
>>>>>>>>
>>>>>>>>> -Daniel
>>>>>>>>>
>>>>>>>>>>> Cc: mesa-dev@lists.freedesktop.org
>>>>>>>>>>> Cc: Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>
>>>>>>>>>>> Cc: Dave Airlie <airlied@gmail.com>
>>>>>>>>>>> Cc: Rob Clark <robdclark@chromium.org>
>>>>>>>>>>> Cc: Kristian H. Kristensen <hoegsberg@google.com>
>>>>>>>>>>> Cc: Michel Dänzer <michel@daenzer.net>
>>>>>>>>>>> Cc: Daniel Stone <daniels@collabora.com>
>>>>>>>>>>> Cc: Sumit Semwal <sumit.semwal@linaro.org>
>>>>>>>>>>> Cc: "Christian König" <christian.koenig@amd.com>
>>>>>>>>>>> Cc: Alex Deucher <alexander.deucher@amd.com>
>>>>>>>>>>> Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
>>>>>>>>>>> Cc: Deepak R Varma <mh12gx2825@gmail.com>
>>>>>>>>>>> Cc: Chen Li <chenli@uniontech.com>
>>>>>>>>>>> Cc: Kevin Wang <kevin1.wang@amd.com>
>>>>>>>>>>> Cc: Dennis Li <Dennis.Li@amd.com>
>>>>>>>>>>> Cc: Luben Tuikov <luben.tuikov@amd.com>
>>>>>>>>>>> Cc: linaro-mm-sig@lists.linaro.org
>>>>>>>>>>> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
>>>>>>>>>>> ---
>>>>>>>>>>>      drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c  |  7 +++++--
>>>>>>>>>>>      drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c | 21 +++++++++++++++++++++
>>>>>>>>>>>      drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h  |  6 ++++++
>>>>>>>>>>>      include/uapi/drm/amdgpu_drm.h           | 10 ++++++++++
>>>>>>>>>>>      4 files changed, 42 insertions(+), 2 deletions(-)
>>>>>>>>>>>
>>>>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>>>>>>>>>> index 65df34c17264..c5386d13eb4a 100644
>>>>>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>>>>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_cs.c
>>>>>>>>>>> @@ -498,6 +498,7 @@ static int amdgpu_cs_parser_bos(struct amdgpu_cs_parser *p,
>>>>>>>>>>>             struct amdgpu_bo *gds;
>>>>>>>>>>>             struct amdgpu_bo *gws;
>>>>>>>>>>>             struct amdgpu_bo *oa;
>>>>>>>>>>> +       bool no_implicit_sync = READ_ONCE(fpriv->vm.no_implicit_sync);
>>>>>>>>>>>             int r;
>>>>>>>>>>>
>>>>>>>>>>>             INIT_LIST_HEAD(&p->validated);
>>>>>>>>>>> @@ -577,7 +578,8 @@ static int amdgpu_cs_parser_bos(struct amdgpu_cs_parser *p,
>>>>>>>>>>>
>>>>>>>>>>>                     e->bo_va = amdgpu_vm_bo_find(vm, bo);
>>>>>>>>>>>
>>>>>>>>>>> -               if (bo->tbo.base.dma_buf && !amdgpu_bo_explicit_sync(bo)) {
>>>>>>>>>>> +               if (bo->tbo.base.dma_buf &&
>>>>>>>>>>> +                   !(no_implicit_sync || amdgpu_bo_explicit_sync(bo))) {
>>>>>>>>>>>                             e->chain = dma_fence_chain_alloc();
>>>>>>>>>>>                             if (!e->chain) {
>>>>>>>>>>>                                     r = -ENOMEM;
>>>>>>>>>>> @@ -649,6 +651,7 @@ static int amdgpu_cs_sync_rings(struct amdgpu_cs_parser *p)
>>>>>>>>>>>      {
>>>>>>>>>>>             struct amdgpu_fpriv *fpriv = p->filp->driver_priv;
>>>>>>>>>>>             struct amdgpu_bo_list_entry *e;
>>>>>>>>>>> +       bool no_implicit_sync = READ_ONCE(fpriv->vm.no_implicit_sync);
>>>>>>>>>>>             int r;
>>>>>>>>>>>
>>>>>>>>>>>             list_for_each_entry(e, &p->validated, tv.head) {
>>>>>>>>>>> @@ -656,7 +659,7 @@ static int amdgpu_cs_sync_rings(struct amdgpu_cs_parser *p)
>>>>>>>>>>>                     struct dma_resv *resv = bo->tbo.base.resv;
>>>>>>>>>>>                     enum amdgpu_sync_mode sync_mode;
>>>>>>>>>>>
>>>>>>>>>>> -               sync_mode = amdgpu_bo_explicit_sync(bo) ?
>>>>>>>>>>> +               sync_mode = no_implicit_sync || amdgpu_bo_explicit_sync(bo) ?
>>>>>>>>>>>                             AMDGPU_SYNC_EXPLICIT : AMDGPU_SYNC_NE_OWNER;
>>>>>>>>>>>                     r = amdgpu_sync_resv(p->adev, &p->job->sync, resv, sync_mode,
>>>>>>>>>>>                                          &fpriv->vm);
>>>>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>>>>>> index c080ba15ae77..f982626b5328 100644
>>>>>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_drv.c
>>>>>>>>>>> @@ -1724,6 +1724,26 @@ int amdgpu_file_to_fpriv(struct file *filp, struct amdgpu_fpriv **fpriv)
>>>>>>>>>>>             return 0;
>>>>>>>>>>>      }
>>>>>>>>>>>
>>>>>>>>>>> +int amdgpu_setparam_ioctl(struct drm_device *dev, void *data,
>>>>>>>>>>> +                         struct drm_file *filp)
>>>>>>>>>>> +{
>>>>>>>>>>> +       struct drm_amdgpu_setparam *setparam = data;
>>>>>>>>>>> +       struct amdgpu_fpriv *fpriv = filp->driver_priv;
>>>>>>>>>>> +
>>>>>>>>>>> +       switch (setparam->param) {
>>>>>>>>>>> +       case AMDGPU_SETPARAM_NO_IMPLICIT_SYNC:
>>>>>>>>>>> +               if (setparam->value)
>>>>>>>>>>> +                       WRITE_ONCE(fpriv->vm.no_implicit_sync, true);
>>>>>>>>>>> +               else
>>>>>>>>>>> +                       WRITE_ONCE(fpriv->vm.no_implicit_sync, false);
>>>>>>>>>>> +               break;
>>>>>>>>>>> +       default:
>>>>>>>>>>> +               return -EINVAL;
>>>>>>>>>>> +       }
>>>>>>>>>>> +
>>>>>>>>>>> +       return 0;
>>>>>>>>>>> +}
>>>>>>>>>>> +
>>>>>>>>>>>      const struct drm_ioctl_desc amdgpu_ioctls_kms[] = {
>>>>>>>>>>>             DRM_IOCTL_DEF_DRV(AMDGPU_GEM_CREATE, amdgpu_gem_create_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>>             DRM_IOCTL_DEF_DRV(AMDGPU_CTX, amdgpu_ctx_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>> @@ -1742,6 +1762,7 @@ const struct drm_ioctl_desc amdgpu_ioctls_kms[] = {
>>>>>>>>>>>             DRM_IOCTL_DEF_DRV(AMDGPU_GEM_VA, amdgpu_gem_va_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>>             DRM_IOCTL_DEF_DRV(AMDGPU_GEM_OP, amdgpu_gem_op_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>>             DRM_IOCTL_DEF_DRV(AMDGPU_GEM_USERPTR, amdgpu_gem_userptr_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>> +       DRM_IOCTL_DEF_DRV(AMDGPU_SETPARAM, amdgpu_setparam_ioctl, DRM_AUTH|DRM_RENDER_ALLOW),
>>>>>>>>>>>      };
>>>>>>>>>>>
>>>>>>>>>>>      static const struct drm_driver amdgpu_kms_driver = {
>>>>>>>>>>> diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>>>>>>>>>> index ddb85a85cbba..0e8c440c6303 100644
>>>>>>>>>>> --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>>>>>>>>>> +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_vm.h
>>>>>>>>>>> @@ -321,6 +321,12 @@ struct amdgpu_vm {
>>>>>>>>>>>             bool                    bulk_moveable;
>>>>>>>>>>>             /* Flag to indicate if VM is used for compute */
>>>>>>>>>>>             bool                    is_compute_context;
>>>>>>>>>>> +       /*
>>>>>>>>>>> +        * Flag to indicate whether implicit sync should always be skipped on
>>>>>>>>>>> +        * this context. We do not care about races at all, userspace is allowed
>>>>>>>>>>> +        * to shoot itself with implicit sync to its fullest liking.
>>>>>>>>>>> +        */
>>>>>>>>>>> +       bool no_implicit_sync;
>>>>>>>>>>>      };
>>>>>>>>>>>
>>>>>>>>>>>      struct amdgpu_vm_manager {
>>>>>>>>>>> diff --git a/include/uapi/drm/amdgpu_drm.h b/include/uapi/drm/amdgpu_drm.h
>>>>>>>>>>> index 0cbd1540aeac..9eae245c14d6 100644
>>>>>>>>>>> --- a/include/uapi/drm/amdgpu_drm.h
>>>>>>>>>>> +++ b/include/uapi/drm/amdgpu_drm.h
>>>>>>>>>>> @@ -54,6 +54,7 @@ extern "C" {
>>>>>>>>>>>      #define DRM_AMDGPU_VM                  0x13
>>>>>>>>>>>      #define DRM_AMDGPU_FENCE_TO_HANDLE     0x14
>>>>>>>>>>>      #define DRM_AMDGPU_SCHED               0x15
>>>>>>>>>>> +#define DRM_AMDGPU_SETPARAM            0x16
>>>>>>>>>>>
>>>>>>>>>>>      #define DRM_IOCTL_AMDGPU_GEM_CREATE    DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_CREATE, union drm_amdgpu_gem_create)
>>>>>>>>>>>      #define DRM_IOCTL_AMDGPU_GEM_MMAP      DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_GEM_MMAP, union drm_amdgpu_gem_mmap)
>>>>>>>>>>> @@ -71,6 +72,7 @@ extern "C" {
>>>>>>>>>>>      #define DRM_IOCTL_AMDGPU_VM            DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_VM, union drm_amdgpu_vm)
>>>>>>>>>>>      #define DRM_IOCTL_AMDGPU_FENCE_TO_HANDLE DRM_IOWR(DRM_COMMAND_BASE + DRM_AMDGPU_FENCE_TO_HANDLE, union drm_amdgpu_fence_to_handle)
>>>>>>>>>>>      #define DRM_IOCTL_AMDGPU_SCHED         DRM_IOW(DRM_COMMAND_BASE + DRM_AMDGPU_SCHED, union drm_amdgpu_sched)
>>>>>>>>>>> +#define DRM_IOCTL_AMDGPU_SETPARAM      DRM_IOW(DRM_COMMAND_BASE + DRM_AMDGPU_SETPARAM, struct drm_amdgpu_setparam)
>>>>>>>>>>>
>>>>>>>>>>>      /**
>>>>>>>>>>>       * DOC: memory domains
>>>>>>>>>>> @@ -306,6 +308,14 @@ union drm_amdgpu_sched {
>>>>>>>>>>>             struct drm_amdgpu_sched_in in;
>>>>>>>>>>>      };
>>>>>>>>>>>
>>>>>>>>>>> +#define AMDGPU_SETPARAM_NO_IMPLICIT_SYNC       1
>>>>>>>>>>> +
>>>>>>>>>>> +struct drm_amdgpu_setparam {
>>>>>>>>>>> +       /* AMDGPU_SETPARAM_* */
>>>>>>>>>>> +       __u32   param;
>>>>>>>>>>> +       __u32   value;
>>>>>>>>>>> +};
>>>>>>>>>>> +
>>>>>>>>>>>      /*
>>>>>>>>>>>       * This is not a reliable API and you should expect it to fail for any
>>>>>>>>>>>       * number of reasons and have fallback path that do not use userptr to
>>>>>>>>>>> --
>>>>>>>>>>> 2.32.0.rc2
>>>>>>>>>>>
>>>
>>> --
>>> Daniel Vetter
>>> Software Engineer, Intel Corporation
>>> https://nam11.safelinks.protection.outlook.com/?url=http%3A%2F%2Fblog.ffwll.ch%2F&amp;data=04%7C01%7Cchristian.koenig%40amd.com%7C517f0d3467324e7ce05008d936581f60%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637600574408265873%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C1000&amp;sdata=tc6ZdgYzOXpER4vpuOiOlyIsr7YTAHLMcuFaNjSs6YE%3D&amp;reserved=0

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