linux-kernel - Re: [PATCH] serdev: Restore serdev_device_write

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Date:   Wed, 17 May 2017 14:46:14 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Stefan Wahren <stefan.wahren@...e.com>
Cc:     Johan Hovold <johan@...nel.org>, Rob Herring <robh@...nel.org>,
        Jiri Slaby <jslaby@...e.com>,
        Sebastian Reichel <sre@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Andrey Smirnov <andrew.smirnov@...il.com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] serdev: Restore serdev_device_write_buf for atomic
 context

On Wed, May 17, 2017 at 01:38:40PM +0200, Stefan Wahren wrote:
> Hi Greg,
> 
> Am 08.05.2017 um 17:18 schrieb Johan Hovold:
> > On Thu, May 04, 2017 at 03:32:53PM -0500, Rob Herring wrote:
> >> On Thu, May 4, 2017 at 11:22 AM, Stefan Wahren <stefan.wahren@...e.com> wrote:
> >>> Am 02.05.2017 um 15:18 schrieb Johan Hovold:
> >>>> On Tue, May 02, 2017 at 07:41:34AM -0500, Rob Herring wrote:
> >>>>> On Tue, May 2, 2017 at 4:06 AM, Johan Hovold <johan@...nel.org> wrote:
> >>>>>> On Fri, Apr 28, 2017 at 01:47:21PM +0200, Stefan Wahren wrote:
> >>>>>>> Starting with commit 6fe729c4bdae ("serdev: Add serdev_device_write
> >>>>>>> subroutine") the function serdev_device_write_buf cannot be used in
> >>>>>>> atomic context anymore (mutex_lock is sleeping). So restore the old
> >>>>>>> behavior.
> >>>>>> Yeah, preventing use in atomic context seems unnecessary, although any
> >>>>>> clients writing must now deal with serialisation themselves (as before,
> >>>>>> and as they should).
> >>>>> We could just remove the mutex for serdev_device_write and always make
> >>>>> the client responsible for serialization.
> >>>> That sounds reasonable.
> >>> So it's unwanted to have 2 write functions (non-atomic, atomic)?
> >> No, it's unwanted to have more than we need.
> >>
> >> Looking closer, we'd also have to ensure the wait for completion is
> >> not called also. So probably better to just leave it as you have done
> >> it.
> > Indeed. Sorry if my reply above was unclear on that point (i.e. that
> > Stefan's patch is still needed regardless of whether we keep the mutex
> > or not).
> >
> > Thanks,
> > Johan
> 
> are you okay with this patch and can you please apply it?

I'll work to catch up on tty/serial patches soon...