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[2001:1c00:c32:7800:5bfa:a036:83f0:f9ec]) by smtp.gmail.com with ESMTPSA id a640c23a62f3a-aab963c5489sm602543066b.186.2024.12.18.12.37.46 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Wed, 18 Dec 2024 12:37:47 -0800 (PST) Message-ID: <84b0f212-cd88-46bb-8e6f-b94ec3eccba6@redhat.com> Date: Wed, 18 Dec 2024 21:37:46 +0100 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH 0/3] media: uvcvideo: Prepare deprecation of nodrop To: Ricardo Ribalda , Laurent Pinchart , Mauro Carvalho Chehab Cc: linux-media@vger.kernel.org, linux-kernel@vger.kernel.org References: <20241217-uvc-deprecate-v1-0-57d353f68f8f@chromium.org> Content-Language: en-US, nl From: Hans de Goede In-Reply-To: <20241217-uvc-deprecate-v1-0-57d353f68f8f@chromium.org> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Ricardo, Thank you for working on this. On 17-Dec-24 10:06 PM, Ricardo Ribalda wrote: > We intend to deprecate the nodrop parameter in the future and adopt the > default behaviour of the other media drivers: drop invalid packages. Actually the default behaviour of other media drivers is: "return buffers with an error to userspace with V4L2_BUF_FLAG_ERROR set in v4l2_buffer.flags". It is not "drop invalid packages". The commit messages of patch 1/3 has some related unclear wording, please fix this. Looking at this I actually have found what arguably is a bug in the UVC driver when nodrop is set, or at least something which we must change before making nodrop=1 the default. Currently uvc_queue_buffer_complete() looks like this: static void uvc_queue_buffer_complete(struct kref *ref) { struct uvc_buffer *buf = container_of(ref, struct uvc_buffer, ref); struct vb2_buffer *vb = &buf->buf.vb2_buf; struct uvc_video_queue *queue = vb2_get_drv_priv(vb->vb2_queue); if ((queue->flags & UVC_QUEUE_DROP_CORRUPTED) && buf->error) { uvc_queue_buffer_requeue(queue, buf); return; } buf->state = buf->error ? UVC_BUF_STATE_ERROR : UVC_BUF_STATE_DONE; vb2_set_plane_payload(&buf->buf.vb2_buf, 0, buf->bytesused); vb2_buffer_done(&buf->buf.vb2_buf, VB2_BUF_STATE_DONE); } Notice how the last line does not propagate buf->error to the videobuf2 code, so when nodrop=1 is set then buffers with errors are not only returned to userspace, they are returned to userspace without V4L2_BUF_FLAG_ERROR getting set in v4l2_buffer.flags . The right thing to do in this case is to set V4L2_BUF_FLAG_ERROR IOW the last line of uvc_queue_buffer_complete() should be changed to: vb2_buffer_done(&buf->buf.vb2_buf, buf->error ? VB2_BUF_STATE_ERROR : VB2_BUF_STATE_DONE); And this should probably be the first patch in a v2 series for this. Regards, Hans