Message-ID: <567951FF.1020203@suse.de>
Date:	Tue, 22 Dec 2015 14:37:03 +0100
From:	Hannes Reinecke <hare@...e.de>
To:	Finn Thain <fthain@...egraphics.com.au>
Cc:	"James E.J. Bottomley" <JBottomley@...n.com>,
	Michael Schmitz <schmitzmic@...il.com>,
	linux-m68k@...r.kernel.org, linux-scsi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	"Martin K. Petersen" <martin.petersen@...cle.com>
Subject: Re: [PATCH v3 18/77] ncr5380: Eliminate USLEEP_WAITLONG delay

On 12/22/2015 01:38 PM, Finn Thain wrote:
>
> On Tue, 22 Dec 2015, Hannes Reinecke wrote:
>
>> On 12/22/2015 02:17 AM, Finn Thain wrote:
>>> Linux 2.1.105 introduced the USLEEP_WAITLONG delay, apparently "needed for
>>> Mustek scanners". It is intended to stall the issue queue for 5 seconds.
>>> There are a number of problems with this.
>>>
>>> 1. Only g_NCR5380 enables the delay, which implies that the other five
>>>      drivers using the NCR5380.c core driver remain incompatible with
>>>      Mustek scanners.
>>>
>>> 2. The delay is not implemented by atari_NCR5380.c, which is problematic
>>>      for re-unifying the two core driver forks.
>>>
>>> 3. The delay is implemented using NCR5380_set_timer() which makes it
>>>      unreliable. A new command queued by the mid-layer cancels the delay.
>>>
>>> 4. The delay is applied indiscriminately in several situations in which
>>>      NCR5380_select() returns -1. These are-- reselection by the target,
>>>      failure of the target to assert BSY, and failure of the target to
>>>      assert REQ. It's clear from the comments that USLEEP_WAITLONG is not
>>>      relevant to the reselection case. And reportedly, these scanners do
>>>      not disconnect.
>>>
>>> 5. atari_NCR5380.c was forked before Linux 2.1.105, so it was spared some
>>>      of the damage done to NCR5380.c. In this case, the atari_NCR5380.c core
>>>      driver was more standard-compliant and may not have needed any
>>>      workaround like the USLEEP_WAITLONG kludge. The compliance issue was
>>>      addressed in the previous patch.
>>>
>>> If these scanners still don't work, we need a better solution. Retrying
>>> selection until EH aborts a command offers equivalent robustness. Bugs in
>>> the existing driver prevent EH working correctly but this is addressed in
>>> a subsequent patch. Remove USLEEP_WAITLONG.
>>>
>>> Signed-off-by: Finn Thain <fthain@...egraphics.com.au>
>>>
>>> ---
>>>    drivers/scsi/NCR5380.c   |   19 +++++--------------
>>>    drivers/scsi/g_NCR5380.c |    1 -
>>>    2 files changed, 5 insertions(+), 15 deletions(-)
>>>
>>> Index: linux/drivers/scsi/NCR5380.c
>>> ===================================================================
>>> --- linux.orig/drivers/scsi/NCR5380.c	2015-12-22 12:15:51.000000000 +1100
>>> +++ linux/drivers/scsi/NCR5380.c	2015-12-22 12:15:52.000000000 +1100
>>> @@ -468,10 +468,6 @@ static void NCR5380_print_phase(struct S
>>>    #ifndef USLEEP_POLL
>>>    #define USLEEP_POLL msecs_to_jiffies(200)
>>>    #endif
>>> -#ifndef USLEEP_WAITLONG
>>> -/* RvC: (reasonable time to wait on select error) */
>>> -#define USLEEP_WAITLONG USLEEP_SLEEP
>>> -#endif
>>>
>>>    /*
>>>     * Function : int should_disconnect (unsigned char cmd)
>>> @@ -619,8 +615,8 @@ static void prepare_info(struct Scsi_Hos
>>>              "can_queue %d, cmd_per_lun %d, "
>>>              "sg_tablesize %d, this_id %d, "
>>>              "flags { %s%s%s%s}, "
>>> -#if defined(USLEEP_POLL) && defined(USLEEP_WAITLONG)
>>> -		 "USLEEP_POLL %lu, USLEEP_WAITLONG %lu, "
>>> +#if defined(USLEEP_POLL) && defined(USLEEP_SLEEP)
>>> +		 "USLEEP_POLL %lu, USLEEP_SLEEP %lu, "
>>>    #endif
>>>              "options { %s} ",
>>>              instance->hostt->name, instance->io_port, instance->n_io_port,
>>> @@ -631,8 +627,8 @@ static void prepare_info(struct Scsi_Hos
>>>              hostdata->flags & FLAG_DTC3181E      ? "DTC3181E "      : "",
>>>              hostdata->flags & FLAG_NO_PSEUDO_DMA ? "NO_PSEUDO_DMA " : "",
>>>              hostdata->flags & FLAG_TOSHIBA_DELAY ? "TOSHIBA_DELAY "  : "",
>>> -#if defined(USLEEP_POLL) && defined(USLEEP_WAITLONG)
>>> -	         USLEEP_POLL, USLEEP_WAITLONG,
>>> +#if defined(USLEEP_POLL) && defined(USLEEP_SLEEP)
>>> +	         USLEEP_POLL, USLEEP_SLEEP,
>>>    #endif
>>>    #ifdef AUTOPROBE_IRQ
>>>              "AUTOPROBE_IRQ "
>> Wouldn't it make more sense to remove the USLEEP_WAITLONG completely?
>>  From what I can see it is meant to indicate that WAITLONG is enabled,
>> but we've just removed that functionality...
>
> Actually, this patch does remove USLEEP_WAITLONG completely. It does not
> remove USLEEP_POLL and USLEEP_SLEEP. In patch 25, the USLEEP_POLL and
> USLEEP_SLEEP stuff is replaced by an algorithm that sleeps while polling.
>
> You are right that adding USLEEP_SLEEP to this snprintf() is a change that
> doesn't really belong here. But since I was changing those lines anyway,
> it seemed like a good time to fix a mistake I made when I first added the
> snprintf() and wrote "USLEEP_POLL, USLEEP_WAITLONG" instead of
> "USLEEP_POLL, USLEEP_SLEEP".
>
> Shall I revise this patch? That will affect patch 25. Or perhaps I should
> add the snprintf() change in the commit log?
>
> Thanks for your review.
>
Na, that's fine. The entire thing got removed in a later patch, so no 
worries.

Reviewed-by: Hannes Reinecke <hare@...e.com>

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		      zSeries & Storage
hare@...e.de			      +49 911 74053 688
SUSE LINUX Products GmbH, Maxfeldstr. 5, 90409 Nürnberg
GF: J. Hawn, J. Guild, F. Imendörffer, HRB 16746 (AG Nürnberg)
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