[EXT] [PATCH 14/65] media: amphion: Delete v4l2_fh synchronously in .release()

[Ming Qian]

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>Jacopo Mondi <jacopo.mondi at ideasonboard.com>
>Subject: [EXT] [PATCH 14/65] media: amphion: Delete v4l2_fh synchronously
>in .release()
>
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>
>From: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>
>The v4l2_fh initialized and added in vpu_v4l2_open() is delete and cleaned up
>when the last reference to the vpu_inst is released. This may happen later than
>at vpu_v4l2_close() time.
>
>Not deleting and cleaning up the v4l2_fh when closing the file handle to the
>video device is not ideal, as the v4l2_fh will still be present in the video device's
>fh_list, and will store a copy of events queued to the video device. There may
>also be other side effects of keeping alive an object that represents an open file
>handle after the file handle is closed.
>
>The v4l2_fh instance is embedded in the vpu_inst structure, and is accessed in
>two different ways:
>
>- in vpu_notify_eos() and vpu_notify_source_change(), to queue V4L2
>  events to the file handle ; and
>
>- through the driver to access the v4l2_fh.m2m_ctx pointer.
>
>The v4l2_fh.m2m_ctx pointer is not touched by v4l2_fh_del() and
>v4l2_fh_exit(). It is set to NULL by the driver when closing the file handle, in
>vpu_v4l2_close().
>
>The vpu_notify_eos() and vpu_notify_source_change() functions are called in
>vpu_set_last_buffer_dequeued() and vdec_handle_resolution_change()
>respectively, only if the v4l2_fh.m2m_ctx pointer is not NULL. There is therefore
>a guarantee that no new event will be queued to the v4l2_fh after
>vpu_v4l2_close() destroys the m2m_ctx.
>
>The vpu_notify_eos() function is also called from vpu_vb2_buf_finish(), which
>is guaranteed to be called for all queued buffers when
>vpu_v4l2_close() calls v4l2_m2m_ctx_release(), and will not be called later.
>
>It is therefore safe to assume that the driver will not touch the v4l2_fh, except
>to check the m2m_ctx pointer, after vpu_v4l2_close() destroys the m2m_ctx.
>We can safely delete and cleanup the v4l2_fh synchronously in
>vpu_v4l2_close().
>
>Signed-off-by: Laurent Pinchart <laurent.pinchart at ideasonboard.com>
>Signed-off-by: Jacopo Mondi <jacopo.mondi at ideasonboard.com>

Reviewed-by: Ming Qian <ming.qian at oss.nxp.com>

>---
> drivers/media/platform/amphion/vpu_v4l2.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/media/platform/amphion/vpu_v4l2.c
>b/drivers/media/platform/amphion/vpu_v4l2.c
>index
>306d94e0f8e79faaacfa35b28e5786860f7bd1ca..57ca6262bb04b356a85e217ef
>51cfb13cb9a0a36 100644
>--- a/drivers/media/platform/amphion/vpu_v4l2.c
>+++ b/drivers/media/platform/amphion/vpu_v4l2.c
>@@ -724,8 +724,6 @@ static int vpu_v4l2_release(struct vpu_inst *inst)
>
>        v4l2_ctrl_handler_free(&inst->ctrl_handler);
>        mutex_destroy(&inst->lock);
>-       v4l2_fh_del(&inst->fh);
>-       v4l2_fh_exit(&inst->fh);
>
>        call_void_vop(inst, cleanup);
>
>@@ -794,6 +792,8 @@ int vpu_v4l2_open(struct file *file, struct vpu_inst
>*inst)
>
>        return 0;
> error:
>+       v4l2_fh_del(&inst->fh);
>+       v4l2_fh_exit(&inst->fh);
>        vpu_inst_put(inst);
>        return ret;
> }
>@@ -813,6 +813,9 @@ int vpu_v4l2_close(struct file *file)
>        call_void_vop(inst, release);
>        vpu_inst_unlock(inst);
>
>+       v4l2_fh_del(&inst->fh);
>+       v4l2_fh_exit(&inst->fh);
>+
>        vpu_inst_unregister(inst);
>        vpu_inst_put(inst);
>
>
>--
>2.49.0