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

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Date:   Mon, 8 May 2017 17:18:58 +0200
From:   Johan Hovold <johan@...nel.org>
To:     Rob Herring <robh@...nel.org>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Johan Hovold <johan@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.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 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