From mboxrd@z Thu Jan 1 00:00:00 1970 From: Jeff Garzik Subject: Re: jgarzik and max-sectors: out of memory Date: Sat, 27 May 2006 16:02:06 -0400 Message-ID: <4478B03E.9060202@garzik.org> References: <4478AA6C.5070305@garzik.org> <4478AD4B.5090404@rtr.ca> Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit Return-path: Received: from srv5.dvmed.net ([207.36.208.214]:35983 "EHLO mail.dvmed.net") by vger.kernel.org with ESMTP id S964931AbWE0UCK (ORCPT ); Sat, 27 May 2006 16:02:10 -0400 In-Reply-To: <4478AD4B.5090404@rtr.ca> Sender: linux-ide-owner@vger.kernel.org List-Id: linux-ide@vger.kernel.org To: Mark Lord Cc: "linux-ide@vger.kernel.org" , Tejun Heo , Alan Cox , Jens Axboe , Hannes Reinecke Mark Lord wrote: > Jeff Garzik wrote: > .. >> Further -- someone with a long ATA memory correct me -- I think that >> we can increase ATA_MAX_PRD beyond 256. Most DMA engines should just >> keep chugging along, provided that we continue to respect the 64k IDE >> DMA boundaries. > > MAX_PRD used to be equal to MAX_SECTORS, as that's the worst case scenario. Not for lba48, which has a larger max-sectors but is still clamped to the same 256 PRD entries... > The only real gotcha I remember from the original IDE driver, > was that some (very few) controllers were buggy with handing > of a sector_count of zero (256), so setting the limit to a slightly > lower value prevented that from ever being a problem. Yeah, a couple of Alan's PATA drivers are fixed at 255. > That was in the days before the block layer could limit the segment count. Ahhhhh, useful to know. Jeff