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

On Tue, May 30, 2017 at 02:42:13PM +0100, Alan Cox wrote:

I sent a second patch recently:

https://patchwork.kernel.org/patch/9725625/

quoted

quoted

Fixes: 18a4208826dd0a13eb06de724c86bba2c225f943 ("imx-serial: Reduce
RX DMA startup latency when opening for reading")

Cc: cphealy@gmail.com
Cc: Peter Senna Tschudin <redacted>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Jiri Slaby <redacted>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andrey Smirnov <redacted>
---

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