Re: [PATCH v2 resend] media: dvb: usb: Fix WARNING in dib0700_i2c_xfer/usb_submit_urb

Alan Stern
2025-03-29T14:31:57Z

On Sat, Mar 29, 2025 at 07:05:49AM +0100, Wolfram Sang wrote:
>
> > In the case of dib0700, it was clear from the source code that the
> > driver uses USB Control transfers to tell the hardware about I2C
> > messages. I don't know if other bridges work in the same way. In
> > theory a bridge could use USB Bulk transfers instead; they aren't
> > subject to this restriction on length-0 reads. Or a bridge could use a
> > Control read transfer but include extra header material along with the
> > actual data, so that a length-0 message wouldn't end up generating a
> > length-0 read.
>
> Fully understood, thanks for your explanation.
>
> > So the short answer is that you would need to find someone who really
> > understands what's going on here -- which I don't. Sorry.
>
> No worries. There are only 5 drivers or so, I will manually check if
> they use a control_read and have no own header. Doesn't sound hard.

Good... Feel free to ask me if you have any questions or need any other
help.

Alan Stern