Re: [RFC, PATCH] imx: serial: Take tty->files_lock opportunistically

[Alan Cox]

> > Fixes: 18a4208826dd0a13eb06de724c86bba2c225f943 ("imx-serial: Reduce
> > RX DMA startup latency when opening for reading")
> >
> > Cc: cphealy@xxxxxxxxx
> > Cc: Peter Senna Tschudin <peter.senna@xxxxxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Jiri Slaby <jslaby@xxxxxxxx>
> > Cc: linux-kernel@xxxxxxxxxxxxxxx
> > Signed-off-by: Andrey Smirnov <andrew.smirnov@xxxxxxxxx>
> > ---
> >
> > Not sure if this is the best way to solve the problem (hence the RFC
> > tag). If anyone has a better idea, or if there's a better fix for this
> > already, please let me know.  
> 
> IMO, the low level serial drivers shouldn't be accessing
> tty->tty_files in the first place. Is being opened for write-only that
> common and is skipping the DMA setup really necessary?

Seconded - the Reduce RX DMA startup latency patch should just be
reverted (and shouldn't ever IMHO have gotten in).

Not all readers and writers to a tty have a file handle any more anyway,
so it's not only icky and layer violating it's fundamentally broken
beyond the locking.

Alan