linux-kernel - Re: [PATCH] n_gsm: Fix write handling for zero bytes written

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Message-ID: <20200818104714.GR2994@atomide.com>
Date:   Tue, 18 Aug 2020 13:47:14 +0300
From:   Tony Lindgren <tony@...mide.com>
To:     Jiri Slaby <jirislaby@...nel.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        linux-serial@...r.kernel.org, linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Subject: Re: [PATCH] n_gsm: Fix write handling for zero bytes written

* Jiri Slaby <jirislaby@...nel.org> [200818 10:14]:
> On 18. 08. 20, 11:56, Tony Lindgren wrote:
> > Hi,
> > 
> > * Jiri Slaby <jirislaby@...nel.org> [200818 08:24]:
> >> On 17. 08. 20, 15:54, Tony Lindgren wrote:
> >>> If write returns zero we currently end up removing the message
> >>> from the queue. Instead of removing the message, we want to just
> >>> break out of the loop just like we already do for error codes.
> >>
> >> When exactly does the only writer (gsmld_output) return zero for
> >> non-zero len parameter?
> > 
> > I ran into this when testing with the WIP serial core PM runtime
> > changes from Andy Shevchenko earlier. If there are also other
> > cases where we have serial drivers return 0, I don't know about
> > them.
> 
> Sorry, I don't understand: my gsmld_output() ignores the return value
> from drivers' write and returns something greater than zero or a
> negative error. What tree/SHA do you run?

Oh right, good catch. I also had my WIP serdev-ngsm patches applied
that uses gsm_serdev_output() and returns the bytes written. Andy's
patches do not touch n_gsm.c.

Hmm sounds like we should also start returning value also from
gsmld_output()? Any objections to making that change?

For reference, Andy's WIP serial cor PM runtime changes are at:

https://gitlab.com/andy-shev/next.git/ topic/uart/rpm-plus

Regards,

Tony