linux-kernel - Re: Linux 3.15: SPARC serial console regression

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Message-ID: <20140615185635.GA22577@ravnborg.org>
Date:	Sun, 15 Jun 2014 20:56:35 +0200
From:	Sam Ravnborg <sam@...nborg.org>
To:	Peter Hurley <peter@...leysoftware.com>
Cc:	Aaro Koskinen <aaro.koskinen@....fi>,
	David Miller <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Seth Bollinger <sethb@...i.com>,
	LinusTorvaldstorvalds@...ux-foundation.org
Subject: Re: Linux 3.15: SPARC serial console regression

Hi Peter.

On Tue, Jun 10, 2014 at 05:20:08PM -0400, Peter Hurley wrote:
> Hi Sam,
> 
> On 06/10/2014 03:24 PM, Sam Ravnborg wrote:
> >>From: Peter Hurley <peter@...leysoftware.com>
> >>Date: Mon, 9 Jun 2014 19:21:43 -0400
> >>Subject: [PATCH] serial: sunsab: Test for no tx data on tx restart
> >>
> >>Commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c,
> >>'serial_core: Fix conditional start_tx on ring buffer not empty'
> >>exposes an incorrect assumption in sunsab's start_tx method; the
> >>tx ring buffer can, in fact, be empty when restarting tx when
> >>performing flow control.

We have a report that commit 717f3bbab3c7628736ef738fdbf3d9a28578c26c
("serial_core: Fix conditional start_tx on ring buffer not empty")
broke at least one more driver:

    Aaro Koskinen <aaro.koskinen@....fi> reported:
    The same problem is present also on PowerPC G5 Xserve (pmac_zilog driver)

And based on code review a third driver is broken:

    Sam Ravnborg <sam@...nborg.org> reported:
    Can you please take a look at sunzilog.c.
    It looks like the same test is missing in sunzilog_start_tx():

This is a regression so we should either revert the above commit
or review and fix the remaining drivers.

	Sam
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