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

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Message-ID: <539F0F32.7080506@hurleysoftware.com>
Date:	Mon, 16 Jun 2014 11:37:22 -0400
From:	Peter Hurley <peter@...leysoftware.com>
To:	Sam Ravnborg <sam@...nborg.org>
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

On 06/15/2014 02:56 PM, Sam Ravnborg wrote:
> 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.

I'm working on the audit right now, but its not entirely accurate to
call this is a regression.

All of these drivers were already broken on resume-from-suspend
and hard flow control restart.

Regards,
Peter Hurley
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