Re: [PATCH] 2.5.15 IDE 61

From: Neil Conway <nconway.list@ukaea.org.uk>
To: Mike Fedyk <mfedyk@matchmail.com>
Cc: vda@port.imtp.ilyichevsk.odessa.ua,
	Martin Dalecki <dalecki@evision-ventures.com>,
	Anton Altaparmakov <aia21@cantab.net>,
	Alan Cox <alan@lxorguk.ukuu.org.uk>,
	Russell King <rmk@arm.linux.org.uk>,
	linux-kernel@vger.kernel.org
Subject: Re: [PATCH] 2.5.15 IDE 61
Date: Fri, 17 May 2002 12:06:45 +0100	[thread overview]
Message-ID: <3CE4E445.3F9F57A3@ukaea.org.uk> (raw)
In-Reply-To: <E177dYp-00083c-00@the-village.bc.nu> <5.1.0.14.2.20020514202811.01fcc1d0@pop.cus.cam.ac.uk> <3CE22B2B.5080506@evision-ventures.com> <200205151138.g4FBcGY13110@Port.imtp.ilyichevsk.odessa.ua> <3CE24CB9.8DFC5821@ukaea.org.uk> <20020517070750.GD627@matchmail.com>

Mike Fedyk wrote:
> On Wed, May 15, 2002 at 12:55:37PM +0100, Neil Conway wrote:
> > You can (and must) safely "touch the cable" in between TCQ commands in
> > the right circumstances.  You are therefore touching the cable while the
> > hwgroup is busy, hence my suggestion that the flag we use to prevent
> > touching the cable during DMA should be named something other than busy.
> Ahh, but with TCQ the concept of busy changes.  The wire (simplified) is
> only busy when the tags are being transfered, otherwise the cable is unused
> unless the cable has been "locked" by one of the devices.

Hmm: "locked by one of the devices": do you mean a DMA transfer for
example?  These are initiated by the host, but proceed asynchronously,
so I'm not sure I'd describe it as being locked "by the device" as
such.  At any rate, the IDE code has to remember that the cable is
asynchronously active until DMA ends...  (Or I suppose it could just
check the hwif BMDMA bits for the active state.)

I don't think you're actually disagreeing with me here btw; if you are
then I've obviously missed your point ;-))

Neil