From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mark Lord Subject: Re: [PATCH 13/13] libata: use PIO for misc ATAPI commands Date: Tue, 27 Nov 2007 18:31:41 -0500 Message-ID: <474CA8DD.3040004@rtr.ca> References: <11961764391983-git-send-email-htejun@gmail.com> <11961764413291-git-send-email-htejun@gmail.com> <20071127165600.39b8c383@the-village.bc.nu> <474CA1E2.1060008@gmail.com> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from rtr.ca ([76.10.145.34]:4364 "EHLO mail.rtr.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757491AbXK0Xbm (ORCPT ); Tue, 27 Nov 2007 18:31:42 -0500 In-Reply-To: <474CA1E2.1060008@gmail.com> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Tejun Heo Cc: Alan Cox , jeff@garzik.org, linux-ide@vger.kernel.org, albertl@mail.com, jens.axboe@oracle.com Tejun Heo wrote: > Alan Cox wrote: .. > Because we can't use DMA uniformly, I went the other way and tried to > use PIO uniformly. Another important point is that the other OS which > is probably the only platform most ATAPI device vendors test against use > PIO for these commands. > >> - Control over the DMA/PIO strategy belongs with the driver. If we mess >> that up it will cost us dearly later. > > And I don't get what we'll lose. Care to deliberate? .. Mmmm.. so what happens with the various controllers that can do PIO using host-DMA and host-queuing ? Dropping to *real* PIO mode can be quite expensive on those, especially when the channel is shared with a hard disk. Curious.