[RFC 20/24] SERIAL: core: add xmit buffer allocation callbacks

[linux@arm.linux.org.uk (Russell King - ARM Linux)]

On Sat, Oct 06, 2012 at 04:49:56PM +0100, Alan Cox wrote:
> On Sat, 06 Oct 2012 13:45:47 +0100
> Russell King <rmk+kernel@arm.linux.org.uk> wrote:
> 
> > This allows drivers (such as OMAP serial) to allocate and free their
> > transmit buffers in a sane manner, rather than working around the
> > buffer allocation provided by serial_core.
> 
> I think this just illustrates how broken the serial_core layering is in
> that drivers can't treat it as a library but get constrained by it.
> 
> Fine for now and actually probably a useful hook to begin removing the
> circ buffers for the kernel generic kfifo and other work that needs doing
> eventually.

Yes, I was thinking about turning the 'default' buffer allocation into
a library call which drivers would set, but I felt that's just asking
for a big patch and problems with new drivers appearing.

We could transition it by providing a default buffer allocation call,
converting all the drivers, and then making that call mandatory.  That
probably would then give us a better path to convert to kfifo.

The view that serial_core should be a library is one that Ted mentioned
when I created serial_core originally - I disagreed at the time, and
I still believe it would've ended up being much more complex - and
hairy - to go that route at that time.  Maybe as things have moved
forward in the tty layer that's changed, but I've been out of tty stuff
for too long to properly comment.