linux-kernel - Re: NEC ND-4550A problems reading DVD-R

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Date:	Fri, 04 Mar 2011 23:16:46 +0100
From:	Jens Axboe <axboe@...nel.dk>
To:	Tejun Heo <tj@...nel.org>
CC:	Stephen Clark <sclark46@...thlink.net>,
	Mark Lord <kernel@...savvy.com>,
	Krzysztof Halasa <khc@...waw.pl>, linux-ide@...r.kernel.org,
	lkml <linux-kernel@...r.kernel.org>, linux-scsi@...r.kernel.org,
	James Bottomley <James.Bottomley@...senPartnership.com>
Subject: Re: NEC ND-4550A problems reading DVD-R

On 2011-03-04 12:07, Tejun Heo wrote:
> (cc'ing Jens and James)
> 
> On Tue, Mar 01, 2011 at 10:47:41AM -0500, Stephen Clark wrote:
>> On 03/01/2011 08:48 AM, Mark Lord wrote:
>>> On 11-03-01 03:01 AM, Tejun Heo wrote:
>>> ..
>>>> I think that's determined by drivers/scsi/sr.h::SR_TIMEOUT which is
>>>> hardcoded to be 30 seconds.  Maybe it's better to move it to use the
>>>> block parameter.  Anyways, the drive actually takes longer than 30secs
>>>> to recognize the media?
>>> That slow behaviour is not uncommon, especially as drives struggle
>>> to recognize various forms of copy-protected media (DVD-Video).
>>> A longer default, or tuneable timeout, would help.
>>
>> I agree with Mark, this should be a user tuneable value. My 2006 LG
>> dvd-rw frequently times out
>> trying to identify the media. But after numerous timeout error
>> messages it usually suceeds.
> 
> I don't think it should be a user tunable value.  It should be
> something automatic.  I mean, how many would know to go some cryptic
> place and increase sr probing timeout?
> 
> At the same time, increasing it for other cases is quite unattractive,
> so it probably would be a good idea to only use higher timeout value
> for the TUR right after media presence change event.
> 
> Anyone interested in doing it?

A higher timeout would be the easy fix. And unless there's a solid way
to detect whether the drive is truly hung or just busy trying to grok
the media, I think it's the only feasible solution.

-- 
Jens Axboe

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