mmc: omap_hsmmc: fix DMA API warning

While booting with rootfs on MMC, the following warning is encountered
on OMAP4430:

omap-dma-engine 4a056000.dma-controller: DMA-API: mapping sg segment longer than device claims to support [len=69632] [max=65536]

This is because the DMA engine has a default maximum segment size of 64K
but HSMMC sets:

        mmc->max_blk_size = 512;       /* Block Length at max can be 1024 */
        mmc->max_blk_count = 0xFFFF;    /* No. of Blocks is 16 bits */
        mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count;
        mmc->max_seg_size = mmc->max_req_size;

which ends up telling the block layer that we support a maximum segment
size of 65535*512, which exceeds the advertised DMA engine capabilities.

Fix this by clamping the maximum segment size to the lower of the
maximum request size and of the DMA engine device used for either DMA
channel.
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

drivers/mmc/host/omap_hsmmc.c

@@ -1909,7 +1909,6 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 	mmc->max_blk_size = 512;       /* Block Length at max can be 1024 */
 	mmc->max_blk_count = 0xFFFF;    /* No. of Blocks is 16 bits */
 	mmc->max_req_size = mmc->max_blk_size * mmc->max_blk_count;
-	mmc->max_seg_size = mmc->max_req_size;
 
 	mmc->caps |= MMC_CAP_MMC_HIGHSPEED | MMC_CAP_SD_HIGHSPEED |
 		     MMC_CAP_WAIT_WHILE_BUSY | MMC_CAP_ERASE | MMC_CAP_CMD23;
@@ -1939,6 +1938,17 @@ static int omap_hsmmc_probe(struct platform_device *pdev)
 		goto err_irq;
 	}
 
+	/*
+	 * Limit the maximum segment size to the lower of the request size
+	 * and the DMA engine device segment size limits.  In reality, with
+	 * 32-bit transfers, the DMA engine can do longer segments than this
+	 * but there is no way to represent that in the DMA model - if we
+	 * increase this figure here, we get warnings from the DMA API debug.
+	 */
+	mmc->max_seg_size = min3(mmc->max_req_size,
+			dma_get_max_seg_size(host->rx_chan->device->dev),
+			dma_get_max_seg_size(host->tx_chan->device->dev));
+
 	/* Request IRQ for MMC operations */
 	ret = devm_request_irq(&pdev->dev, host->irq, omap_hsmmc_irq, 0,
 			mmc_hostname(mmc), host);