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Date: Sat, 14 Jul 2007 00:03:58 +0400 From: Sergei Shtylyov <sshtylyov@...mvista.com> To: Mark Lord <lkml@....ca> Cc: Mark Lord <liml@....ca>, Alan Cox <alan@...rguk.ukuu.org.uk>, Bartlomiej Zolnierkiewicz <bzolnier@...il.com>, Suleiman Souhlal <ssouhlal@...ebsd.org>, linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/3] Make the IDE DMA timeout modifiable Mark Lord wrote: >>>> The original question concerned specifically the DMA command >>>> timeout which is twice more than the usual one, WAIT_CMD (10 seconds)... >>> When a drive is in standby, we don't send it anything special to wake >>> up. >>> So even DMA commands have to have a long enough timeout to allow >>> for spinning up. >> Yes, but why *twice* as long as the others? > I would guess simply because DMA has to transfer up to 256 sectors of data, > possibly with sector reallocations, in addition to waiting for the drive > to spin up. Other commands don't. What?! PIO commands don't have to do this as well? :-) > At the time that was coded (?), I suspect that PIO READ/WRITE commands > were fed data as it became available to/from the drive. This may or may I don't see *any* difference with the DMA commands here -- the drive has always been free to assert and deassert DMARQ at its well. > not still be the case, but it does imply that they don't need to hang > around as long on the timeouts as do DMA commands (which have to wait > for *everything* to be transferred). Ah, that makes sense -- during PIO interrupts happen a lot more often. 20 secs still seem to be too much. > Cheers MBR, Sergei PS: Your mail server still keeps bouncing me off. :-( - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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