From: Ai Chao <aichao@xxxxxxxxxx>
The Alcor Corp. Slave camera (1b17:6684 and 2017:0011) returns a wrong
dwMaxPayloadTransferSize value for compressed formats. Valid values are
typically up to 3072 bytes per interval (for high-speed, high-bandwidth
devices), and those faulty devices request 2752512 bytes per interval.
This is a firmware issue, but the manufacturer cannot provide a fixed
firmware.
Fix this by checking the dwMaxPayloadTransferSize field, and hardcoding
a value of 1024 if it exceeds 3072 for compressed formats transferred
over isochronous endpoints. While at it, document the other quirk that
handles a bandwidth issue for uncompressed formats.
Signed-off-by: Ai Chao <aichao@xxxxxxxxxx>
---
I have dropped the Reviewed-by tags as the patch has changed
significantly.
Ricardo, do you know if the 3072 bytes limit is fine with super-speed
devices, or does it need to be increased ?
---
drivers/media/usb/uvc/uvc_video.c | 31 +++++++++++++++++++++++++++++++
1 file changed, 31 insertions(+)
diff --git a/drivers/media/usb/uvc/uvc_video.c b/drivers/media/usb/uvc/uvc_video.c
index d4b023d4de7c..c6351d3b24cf 100644
--- a/drivers/media/usb/uvc/uvc_video.c
+++ b/drivers/media/usb/uvc/uvc_video.c
@@ -200,6 +200,20 @@ static void uvc_fixup_video_ctrl(struct uvc_streaming *stream,
if ((ctrl->dwMaxPayloadTransferSize & 0xffff0000) == 0xffff0000)
ctrl->dwMaxPayloadTransferSize &= ~0xffff0000;
+ /*
+ * Many devices report an incorrect dwMaxPayloadTransferSize value. The
+ * most common issue is devices requesting the maximum possible USB
+ * bandwidth (3072 bytes per interval for high-speed, high-bandwidth
+ * isochronous endpoints) while they actually require less, preventing
+ * multiple cameras from being used at the same time due to bandwidth
+ * overallocation.
+ *
+ * For those devices, replace the dwMaxPayloadTransferSize value based
+ * on an estimation calculated from the frame format and size. This is
+ * only possible for uncompressed formats, as not enough information is
+ * available to reliably estimate the bandwidth requirements for
+ * compressed formats.
+ */
if (!(format->flags & UVC_FMT_FLAG_COMPRESSED) &&
stream->dev->quirks & UVC_QUIRK_FIX_BANDWIDTH &&
stream->intf->num_altsetting > 1) {
@@ -236,6 +250,23 @@ static void uvc_fixup_video_ctrl(struct uvc_streaming *stream,
ctrl->dwMaxPayloadTransferSize = bandwidth;
}
+
+ /*
+ * Another issue is with devices that report a transfer size that
+ * greatly exceeds the maximum supported by any existing USB version
+ * for isochronous transfers. For instance, the "Slave camera" devices
+ * from Alcor Corp. (2017:0011 and 1b17:66B8) request 2752512 bytes per
+ * interval.
+ *
+ * For uncompressed formats, this can be addressed by the FIX_BANDWIDTH
+ * quirk, but for compressed format we can't meaningfully estimate the
+ * required bandwidth. Just hardcode it to 1024 bytes per interval,
+ * which should be large enough for compressed formats.
+ */
+ if ((format->flags & UVC_FMT_FLAG_COMPRESSED) &&
+ ctrl->dwMaxPayloadTransferSize > 3072 &&
+ stream->intf->num_altsetting > 1)
+ ctrl->dwMaxPayloadTransferSize = 1024;
}
static size_t uvc_video_ctrl_size(struct uvc_streaming *stream)
--
Regards,
Laurent Pinchart
