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    Subject[PATCH v6 06/15] dma-buf/sync_file: Support (E)POLLPRI
    Date
    From: Rob Clark <robdclark@chromium.org>

    Allow userspace to use the EPOLLPRI/POLLPRI flag to indicate an urgent
    wait (as opposed to a "housekeeping" wait to know when to cleanup after
    some work has completed). Usermode components of GPU driver stacks
    often poll() on fence fd's to know when it is safe to do things like
    free or reuse a buffer, but they can also poll() on a fence fd when
    waiting to read back results from the GPU. The EPOLLPRI/POLLPRI flag
    lets the kernel differentiate these two cases.

    Signed-off-by: Rob Clark <robdclark@chromium.org>
    ---
    drivers/dma-buf/sync_file.c | 8 ++++++++
    1 file changed, 8 insertions(+)

    diff --git a/drivers/dma-buf/sync_file.c b/drivers/dma-buf/sync_file.c
    index 418021cfb87c..cbe96295373b 100644
    --- a/drivers/dma-buf/sync_file.c
    +++ b/drivers/dma-buf/sync_file.c
    @@ -192,6 +192,14 @@ static __poll_t sync_file_poll(struct file *file, poll_table *wait)
    {
    struct sync_file *sync_file = file->private_data;

    + /*
    + * The POLLPRI/EPOLLPRI flag can be used to signal that
    + * userspace wants the fence to signal ASAP, express this
    + * as an immediate deadline.
    + */
    + if (poll_requested_events(wait) & EPOLLPRI)
    + dma_fence_set_deadline(sync_file->fence, ktime_get());
    +
    poll_wait(file, &sync_file->wq, wait);

    if (list_empty(&sync_file->cb.node) &&
    --
    2.39.1
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