From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Tue, 1 Feb 2011 11:03:48 +0000
Subject: [PATCH] mmci: make sure DMA transfers wait for FIFO drain
In-Reply-To: <1296509980-29987-1-git-send-email-linus.walleij@linaro.org>
References: <1296509980-29987-1-git-send-email-linus.walleij@linaro.org>
Message-ID: <20110201110348.GB31216@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Mon, Jan 31, 2011 at 10:39:40PM +0100, Linus Walleij wrote:
> The DMA mode also needs to wait until the FIFO is drained before
> enabling the MCI_DATAEND IRQ.

Hmm.  This will cause attempted DMA usage on ARM MMCI primecells to get
stuck as we'll wait for the never-delivered callback.

With the code I have in place, you'll notice I have:

        /* Wait up to 1ms for the DMA to complete */
        for (i = 0; ; i++) {
                status = readl(host->base + MMCISTATUS);
                if (!(status & MCI_RXDATAAVLBLMASK) || i >= 100)
                        break;
                udelay(10);
        }

This waits for the DMA controller to read the last data out of the FIFO
before allowing the request to complete.  As it has a timeout, it is
able to detect ARMs broken DMA setup on their MMCI/DMAC, and disable DMA
support for this primecell rather than getting stuck.

This may be sufficient without using the DMA callbacks.