linux-kernel - Re: [PATCH 1/3] Make the IDE DMA timeout modifiable

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Message-ID: <4697D425.7000300@rtr.ca>
Date:	Fri, 13 Jul 2007 15:36:05 -0400
From:	Mark Lord <liml@....ca>
To:	Sergei Shtylyov <sshtylyov@...mvista.com>
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Suleiman Souhlal <ssouhlal@...ebsd.org>,
	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/3] Make the IDE DMA timeout modifiable

Sergei Shtylyov wrote:
> Mark Lord wrote:
> 
>>> O> >>    BTW, why the timeout is so damn long? 2*WAIT_CMD is 20 secs, 
>>> and if DMA is not complete or interrupt pending, it may wait 10 more secs...
..
>> I've lost the original question from this thread, but the idea of the 
> 
>    The original question concerned specifically the DMA command timeout 
> which is twice more than the usual one, WAIT_CMD (10 seconds).
> 
>> longish
>> timeouts was that drive *may* be spun down ("standby"), and thus have 
>> to spin
>> up again to complete media commands.  Back then, drives were much 
>> slower at
>> spinning up than nowadays, and the ATA spec says to allow up to 30 
>> seconds.
> 
>    Well, that doesn't explain the DMA case.

When a drive is in standby, we don't send it anything special to wake up.
So even DMA commands have to have a long enough timeout to allow
for spinning up.

Cheers
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