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Date: Thu, 8 Apr 2021 11:34:48 +0200
From: Christian König <christian.koenig@....com>
To: David Stevens <stevensd@...omium.org>
Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>,
Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>,
Sumit Semwal <sumit.semwal@...aro.org>,
ML dri-devel <dri-devel@...ts.freedesktop.org>,
open list <linux-kernel@...r.kernel.org>,
Linux Media Mailing List <linux-media@...r.kernel.org>,
"moderated list:DMA BUFFER SHARING FRAMEWORK"
<linaro-mm-sig@...ts.linaro.org>
Subject: Re: [PATCH] Revert "drm/syncobj: use dma_fence_get_stub"
Am 08.04.21 um 11:30 schrieb David Stevens:
> On Thu, Apr 8, 2021 at 4:03 PM Christian König <christian.koenig@....com> wrote:
>> Am 08.04.21 um 06:59 schrieb David Stevens:
>>> From: David Stevens <stevensd@...omium.org>
>>>
>>> This reverts commit 86bbd89d5da66fe760049ad3f04adc407ec0c4d6.
>>>
>>> Using the singleton stub fence in drm_syncobj_assign_null_handle means
>>> that all syncobjs created in an already signaled state or any syncobjs
>>> signaled by userspace will reference the singleton fence when exported
>>> to a sync_file. If those sync_files are queried with SYNC_IOC_FILE_INFO,
>>> then the timestamp_ns value returned will correspond to whenever the
>>> singleton stub fence was first initialized. This can break the ability
>>> of userspace to use timestamps of these fences, as the singleton stub
>>> fence's timestamp bears no relationship to any meaningful event.
>> And why exactly is having the timestamp of the call to
>> drm_syncobj_assign_null_handle() better?
> The timestamp returned by SYNC_IOC_FILE_INFO is the "timestamp of
> status change in nanoseconds". If userspace signals the fence with
> DRM_IOCTL_SYNCOBJ_SIGNAL, then a timestamp from
> drm_syncobj_assign_null_handle corresponds to the status change. If
> userspace sets DRM_SYNCOBJ_CREATE_SIGNALED when creating a fence, then
> the status change happens immediately upon creation, which again
> corresponds to when drm_syncobj_assign_null_handle gets called.
Ok, that makes sense.
>
>> Additional if you really need that please don't revert the patch.
>> Instead provide a function which returns a newly initialized stub fence
>> in the dma_fence.c code.
> Ack.
Just add a something like dma_fence_get_new_stub() with kmalloc(),
dma_fence_init() and dma_fence_signal().
Shouldn't be more than a six liner.
Thanks,
Christian.
>
> -David
>
>> Regards,
>> Christian.
>>
>>> Signed-off-by: David Stevens <stevensd@...omium.org>
>>> ---
>>> drivers/gpu/drm/drm_syncobj.c | 58 ++++++++++++++++++++++++++---------
>>> 1 file changed, 44 insertions(+), 14 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/drm_syncobj.c b/drivers/gpu/drm/drm_syncobj.c
>>> index 349146049849..7cc11f1a83f4 100644
>>> --- a/drivers/gpu/drm/drm_syncobj.c
>>> +++ b/drivers/gpu/drm/drm_syncobj.c
>>> @@ -211,6 +211,21 @@ struct syncobj_wait_entry {
>>> static void syncobj_wait_syncobj_func(struct drm_syncobj *syncobj,
>>> struct syncobj_wait_entry *wait);
>>>
>>> +struct drm_syncobj_stub_fence {
>>> + struct dma_fence base;
>>> + spinlock_t lock;
>>> +};
>>> +
>>> +static const char *drm_syncobj_stub_fence_get_name(struct dma_fence *fence)
>>> +{
>>> + return "syncobjstub";
>>> +}
>>> +
>>> +static const struct dma_fence_ops drm_syncobj_stub_fence_ops = {
>>> + .get_driver_name = drm_syncobj_stub_fence_get_name,
>>> + .get_timeline_name = drm_syncobj_stub_fence_get_name,
>>> +};
>>> +
>>> /**
>>> * drm_syncobj_find - lookup and reference a sync object.
>>> * @file_private: drm file private pointer
>>> @@ -344,18 +359,24 @@ void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
>>> }
>>> EXPORT_SYMBOL(drm_syncobj_replace_fence);
>>>
>>> -/**
>>> - * drm_syncobj_assign_null_handle - assign a stub fence to the sync object
>>> - * @syncobj: sync object to assign the fence on
>>> - *
>>> - * Assign a already signaled stub fence to the sync object.
>>> - */
>>> -static void drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
>>> +static int drm_syncobj_assign_null_handle(struct drm_syncobj *syncobj)
>>> {
>>> - struct dma_fence *fence = dma_fence_get_stub();
>>> + struct drm_syncobj_stub_fence *fence;
>>>
>>> - drm_syncobj_replace_fence(syncobj, fence);
>>> - dma_fence_put(fence);
>>> + fence = kzalloc(sizeof(*fence), GFP_KERNEL);
>>> + if (fence == NULL)
>>> + return -ENOMEM;
>>> +
>>> + spin_lock_init(&fence->lock);
>>> + dma_fence_init(&fence->base, &drm_syncobj_stub_fence_ops,
>>> + &fence->lock, 0, 0);
>>> + dma_fence_signal(&fence->base);
>>> +
>>> + drm_syncobj_replace_fence(syncobj, &fence->base);
>>> +
>>> + dma_fence_put(&fence->base);
>>> +
>>> + return 0;
>>> }
>>>
>>> /* 5s default for wait submission */
>>> @@ -469,6 +490,7 @@ EXPORT_SYMBOL(drm_syncobj_free);
>>> int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
>>> struct dma_fence *fence)
>>> {
>>> + int ret;
>>> struct drm_syncobj *syncobj;
>>>
>>> syncobj = kzalloc(sizeof(struct drm_syncobj), GFP_KERNEL);
>>> @@ -479,8 +501,13 @@ int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
>>> INIT_LIST_HEAD(&syncobj->cb_list);
>>> spin_lock_init(&syncobj->lock);
>>>
>>> - if (flags & DRM_SYNCOBJ_CREATE_SIGNALED)
>>> - drm_syncobj_assign_null_handle(syncobj);
>>> + if (flags & DRM_SYNCOBJ_CREATE_SIGNALED) {
>>> + ret = drm_syncobj_assign_null_handle(syncobj);
>>> + if (ret < 0) {
>>> + drm_syncobj_put(syncobj);
>>> + return ret;
>>> + }
>>> + }
>>>
>>> if (fence)
>>> drm_syncobj_replace_fence(syncobj, fence);
>>> @@ -1322,8 +1349,11 @@ drm_syncobj_signal_ioctl(struct drm_device *dev, void *data,
>>> if (ret < 0)
>>> return ret;
>>>
>>> - for (i = 0; i < args->count_handles; i++)
>>> - drm_syncobj_assign_null_handle(syncobjs[i]);
>>> + for (i = 0; i < args->count_handles; i++) {
>>> + ret = drm_syncobj_assign_null_handle(syncobjs[i]);
>>> + if (ret < 0)
>>> + break;
>>> + }
>>>
>>> drm_syncobj_array_free(syncobjs, args->count_handles);
>>>
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