Hi Laurent, Laurent Pinchart wrote: > Hi Sakari, > > On Monday 29 June 2015 10:23:34 Sakari Ailus wrote: >> Helen Fornazier wrote: >>> According to the V4L2 API, the VIDIOC_STREAMON ioctl should return EPIPE >>> when the pipeline configuration is invalid. >>> >>> As the .vidioc_streamon in the v4l2_ioctl_ops usually forwards the error >>> caused by the v4l2_subdev_link_validate_default (if it is in use), it >>> should return -EPIPE if it detects a format mismatch in the pipeline >>> configuration >> >> Only link configuration errors have yielded -EPIPE so far, sub-device >> format configuration error has returned -INVAL instead as you noticed. > > It should also be noted that while v4l2_subdev_link_validate() will return - > EINVAL in case of error, the only driver that performs custom link validation > (omap3isp/ispccdc.c) will return -EPIPE. Good point. That has escaped me until now. >> There are not many sources of -EINVAL while enabling streaming and all >> others are directly caused by the application; I lean towards thinking >> the code is good as it was. The documentation could be improved though. >> It may not be clear which error codes could be caused by different >> conditions. >> >> The debug level messages from media module >> (drivers/media/media-entity.c) do provide more information if needed, >> albeit this certainly is not an application interface. >> >> I wonder what others think. > > There's a discrepancy between the implementation and the documentation, so at > least one of them need to be fixed. -EPIPE would be coherent with the > documentation and seems appropriately named, but another error code would > allow userspace to tell link configuration and format configuration problems > apart. That was the original intent, I think. > Do you think -EINVAL is the most appropriate error code for format > configuration ? It's already used to indicate that the stream type is invalid > or that not enough buffers have been allocated, and is also used by drivers > directly for various purposes. That's true, it's been used also for that purpose. At the time this certainly was not the primary concern. If you can think of a better error code for the purpose (than EINVAL) I'm certainly fine with using one. I still think that -EPIPE is worse for telling about incorrect format configuration than -EINVAL since it's relatively easy to avoid -EINVAL for the documented reasons. -- Kind regards, Sakari Ailus sakari.ailus@xxxxxxxxxxxxxxx -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
