linux-kernel - Re: [PATCH 4/7] mmc: at91_mci: add multiwrite switch

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Date:	Mon, 9 Jun 2008 12:42:49 +0200
From:	Pierre Ossman <drzeus@...eus.cx>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Linux Kernel list <linux-kernel@...r.kernel.org>,
	Andrew Victor <linux@...im.org.za>,
	Eric BENARD <ebenard@...e.fr>,
	ARM Linux Mailing List 
	<linux-arm-kernel@...ts.arm.linux.org.uk>
Subject: Re: [PATCH 4/7] mmc: at91_mci: add multiwrite switch

On Sun, 1 Jun 2008 15:42:52 +0100
Russell King - ARM Linux <linux@....linux.org.uk> wrote:

> If Pierre wants to remove the MULTIWRITE flag, I'd like to hear his
> solution for the pxamci driver, where the only way to ascertain how
> many bytes were transmitted may be to walk the SG list comparing the
> DMA pointer with what was in the hardware DMA engine at the time.
> Maybe.

You set bytes_xfered to 0. As mentioned in my previous mail, I had a
chat with Jens about this and upper layers can only expect to get the
lower bound in how many bytes were written. Other hardware/drivers
already behaves like this so there is no point in crippling the MMC
layer in an effort to give nicer guarantees.

This is why I asked people to audit their drivers to make sure it's
the lower bound that's returned, but I've not received much in the way
of replies.

Rgds
Pierre

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