linux-kernel - Re: sata_nv and dynamically changing DMA mask?

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Message-ID: <20071030100542.3efe01ee@the-village.bc.nu>
Date:	Tue, 30 Oct 2007 10:05:42 +0000
From:	Alan Cox <alan@...rguk.ukuu.org.uk>
To:	Robert Hancock <hancockr@...w.ca>
Cc:	linux-kernel <linux-kernel@...r.kernel.org>,
	ide <linux-ide@...r.kernel.org>
Subject: Re: sata_nv and dynamically changing DMA mask?

On Mon, 29 Oct 2007 22:17:40 -0600
Robert Hancock <hancockr@...w.ca> wrote:

> In the sata_nv driver, when running in ADMA mode, we can do 64-bit DMA. 
> However, when an ATAPI device like a DVD drive is connected, we can't 
> use ADMA mode, and so we have to abide by the restrictions of a normal 
> SFF ATA controller and can only do 32-bit DMA. We detect this and try to 
> set the blk_queue_bounce_limit, blk_queue_segment_boundary and 
> blk_queue_max_hw_segments to the values corresponding to a normal SFF 
> controller.

What about the DMA padding buffer from nv_adma_port_start and internal
buffers for commands like request sense that don't come via the request
queue directly.

Also it seems nv_adma_use_reg_mode() can decide to send other commands
via the non ADMA interface even for ATA devices. Are we 100% certain it
never decides to let through a command with DMA via the register
interface in this case - what do you see if you instrument the function ?

Alan
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