linux-kernel - [RFC PATCH v2 11/16] mmc: omap_hsmmc: limit max

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Message-Id: <1349982281-10785-12-git-send-email-mporter@ti.com>
Date:	Thu, 11 Oct 2012 15:04:36 -0400
From:	Matt Porter <mporter@...com>
To:	Tony Lindgren <tony@...mide.com>, Sekhar Nori <nsekhar@...com>,
	Grant Likely <grant.likely@...retlab.ca>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Benoit Cousson <b-cousson@...com>,
	Russell King <linux@....linux.org.uk>,
	Vinod Koul <vinod.koul@...el.com>,
	Rob Landley <rob@...dley.net>, Chris Ball <cjb@...top.org>
Cc:	Devicetree Discuss <devicetree-discuss@...ts.ozlabs.org>,
	Linux OMAP List <linux-omap@...r.kernel.org>,
	Linux ARM Kernel List <linux-arm-kernel@...ts.infradead.org>,
	Linux DaVinci Kernel List 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Documentation List <linux-doc@...r.kernel.org>,
	Linux MMC List <linux-mmc@...r.kernel.org>,
	Linux SPI Devel List 
	<spi-devel-general@...ts.sourceforge.net>,
	Arnd Bergmann <arnd@...db.de>, Dan Williams <djbw@...com>,
	Rob Herring <rob.herring@...xeda.com>
Subject: [RFC PATCH v2 11/16] mmc: omap_hsmmc: limit max_segs with the EDMA DMAC

The EDMA DMAC has a hardware limitation that prevents supporting
scatter gather lists with any number of segments. Since the EDMA
DMA Engine driver sets the maximum segments to 16, we do the
same.

TODO: this will be replaced once the DMA Engine API supports an
API to query the DMAC's segment size limit.

Signed-off-by: Matt Porter <mporter@...com>
---
 drivers/mmc/host/omap_hsmmc.c |   10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/mmc/host/omap_hsmmc.c b/drivers/mmc/host/omap_hsmmc.c
index b327cd0..52bab01 100644
--- a/drivers/mmc/host/omap_hsmmc.c
+++ b/drivers/mmc/host/omap_hsmmc.c
@@ -1828,6 +1828,16 @@ static int __devinit omap_hsmmc_probe(struct platform_device *pdev)
 	 * as we want. */
 	mmc->max_segs = 1024;
 
+	/* Eventually we should get our max_segs limitation for EDMA by
+	 * querying the dmaengine API */
+	if (pdev->dev.of_node) {
+		struct device_node *parent = pdev->dev.of_node->parent;
+		struct device_node *node;
+		node = of_find_node_by_name(parent, "edma");
+		if (node)
+			mmc->max_segs = 16;
+	}
+
 	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;
-- 
1.7.9.5

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