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 18:34:43 -0500 Message-ID: <474CA993.3080703@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> <474CA8DD.3040004@rtr.ca> 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]:2873 "EHLO mail.rtr.ca" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757362AbXK0Xep (ORCPT ); Tue, 27 Nov 2007 18:34:45 -0500 In-Reply-To: <474CA8DD.3040004@rtr.ca> 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 Mark Lord wrote: > 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. .. Or, for that matter, shared with a port multiplier and several other devices ?