Greg KH wrote:
>
> On Fri, May 19, 2000 at 12:00:21PM -0500, Al Borchers wrote:
> >
> > Our driver has a problem with select--select reports our device is ready
> > for writing, but write sometimes returns -EAGAIN.
>
> Not to say that the driver shouldn't be fixed to work properly though :)
I fixed this problem by having chars_in_buffer return 256 when the write_urb
status was -EINPROGRESS. The normal_poll function in the line discipline
code (drivers/char/n_tty.c) handles select and poll. If the driver reports
chars_in_buffer is less than 256 it assumes there is room to write more. So
if we aren't ready for a write (for example, status==-EINPROGRESS) we have
to have chars_in_buffer report at least 256.
Brian already figured this out in the Keyspan driver, but his chars_in_buffer
only returns 256 if transmit is throttled--that is right, but not enough.
Keyspan has the same problem with select as the Digi driver--select thinks
the port is writable when -EINPROGRESS is set, but it is not.
-- Al
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