linux-kernel - Re: [PATCH] libata: always use polling SETXFER

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Date:	Fri, 25 May 2007 14:52:06 +0200
From:	Tejun Heo <htejun@...il.com>
To:	Jeff Garzik <jeff@...zik.org>
CC:	Alan Cox <alan@...rguk.ukuu.org.uk>, linux-ide@...r.kernel.org,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] libata: always use polling SETXFER

Jeff Garzik wrote:
> Tejun Heo wrote:
>> So, I don't think the problem exists for SATA in the first place.  At
>> least there hasn't been any report of it and doing SETXFER by polling
>> can handle all the existing cases.  We can and probably should deal with
>> such SATA devices when and if they come up.  How are we gonna verify the
>> controller doesn't crap itself and ahci TF register monitoring HSM can
>> work around the weirdo when we don't have any such device?  Even if we
>> determine that we need to do HSM over intelligent SATA controller now, I
>> think we still need to push polling SETXFER first to take care of the
>> existing cases.
> 
> Doing SETXFER by polling only handles the cases where the driver
> actually honors ATA_TFLAG_POLLING, which is /not/ always the case.
> 
> If the new policy ensures that it continues to be OK to /not/ honor
> ATA_TFLAG_POLLING -- thus limiting SETXFER polling assumptions to older
> hardware -- that's fine, and it merely needs to be documented.

Basically this flag applies to drivers which is SFF compliant, at least
at TF interface level.  There also are other flags/callbacks which only
apply to SFF or BMDMA.  It would be nice to separate them out in the
long term and yeah it needs documentation.

> But let us not make the assumption that this bandaid fixes all cases,
> because the bandaid is not applied in all cases.

It covers all the known cases but I agree that SFF specific things
certainly need documentation.

Thanks.

-- 
tejun
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