linux-kernel - Re: libata passthru: support PIO multi commands

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Message-ID: <46703A2D.6000207@rtr.ca>
Date:	Wed, 13 Jun 2007 14:40:45 -0400
From:	Mark Lord <liml@....ca>
To:	albertl@...l.com
Cc:	Alan Cox <alan@...rguk.ukuu.org.uk>, Jeff Garzik <jeff@...zik.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	IDE/ATA development list <linux-ide@...r.kernel.org>
Subject: Re: libata passthru: support PIO multi commands

Albert Lee wrote:
> ..
> It looks like the ATA passthru commands contain more information than
> what libata needs to execute a command.
> 
> e.g. protocol number:
>      libata could possibly infer the protocol from the command opcode.
> 
> e.g. multi_count:
>      libata caches dev->multi_count. Passing multi_count along with
>      each passthru command looks useless for libata.     
> 
> e.g. t_dir:
>      libata could possible infer the direction from the command opcode
>      or from the protocol number (e.g. 4: PIO_IN / 5: PIO_OUT).

I wonder if the *intent* of the specification was that the low-level driver
should perform whatever setup is necessary to issue the command as given.

So if the command specifies a multcount of 8, then the LLD should issue the
appropriate initialization commands to use a multcount of 8, and then issue
the given R/W MULT command, and then perhaps reset the multcount back to
what it was normally (beforehand) ?

Ditto for the others.

I am *not* proposing that we actually do it this way,
but rather just suggesting a possible rationale.

What does the SAT spec say?  Any further hints as to the intent?

Cheers
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