linux-kernel - [PATCH 2/2 v2] mmc_spi: lock the SPI bus when accessing the card

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Message-Id: <1253235134-25571-1-git-send-email-vapier@gentoo.org>
Date:	Thu, 17 Sep 2009 20:52:14 -0400
From:	Mike Frysinger <vapier@...too.org>
To:	spi-devel-general@...ts.sourceforge.net,
	David Brownell <dbrownell@...rs.sourceforge.net>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, Yi Li <yi.li@...log.com>
Subject: [PATCH 2/2 v2] mmc_spi: lock the SPI bus when accessing the card

From: Yi Li <yi.li@...log.com>

The MMC/SPI spec does not play well with typical SPI design -- it often
needs to send out a command in one message, read a response, then do some
other arbitrary step.  Since we can't let another SPI client use the bus
during this time, use the new SPI lock/unlock functions to provide the
required exclusivity.

Signed-off-by: Yi Li <yi.li@...log.com>
Signed-off-by: Mike Frysinger <vapier@...too.org>
---
v2
	- drop now unused maybe_count_child as pointed out by H Hartley Sweeten

 drivers/mmc/host/mmc_spi.c |   41 ++---------------------------------------
 1 files changed, 2 insertions(+), 39 deletions(-)

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index a461017..c3563a7 100644
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1084,6 +1084,7 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
 #endif
 
 	/* issue command; then optionally data and stop */
+	spi_lock_bus(host->spi);
 	status = mmc_spi_command_send(host, mrq, mrq->cmd, mrq->data != NULL);
 	if (status == 0 && mrq->data) {
 		mmc_spi_data_do(host, mrq->cmd, mrq->data, mrq->data->blksz);
@@ -1092,7 +1093,7 @@ static void mmc_spi_request(struct mmc_host *mmc, struct mmc_request *mrq)
 		else
 			mmc_cs_off(host);
 	}
-
+	spi_unlock_bus(host->spi);
 	mmc_request_done(host->mmc, mrq);
 }
 
@@ -1294,18 +1295,6 @@ struct count_children {
 	struct bus_type	*bus;
 };
 
-static int maybe_count_child(struct device *dev, void *c)
-{
-	struct count_children *ccp = c;
-
-	if (dev->bus == ccp->bus) {
-		if (ccp->n)
-			return -EBUSY;
-		ccp->n++;
-	}
-	return 0;
-}
-
 static int mmc_spi_probe(struct spi_device *spi)
 {
 	void			*ones;
@@ -1337,32 +1326,6 @@ static int mmc_spi_probe(struct spi_device *spi)
 		return status;
 	}
 
-	/* We can use the bus safely iff nobody else will interfere with us.
-	 * Most commands consist of one SPI message to issue a command, then
-	 * several more to collect its response, then possibly more for data
-	 * transfer.  Clocking access to other devices during that period will
-	 * corrupt the command execution.
-	 *
-	 * Until we have software primitives which guarantee non-interference,
-	 * we'll aim for a hardware-level guarantee.
-	 *
-	 * REVISIT we can't guarantee another device won't be added later...
-	 */
-	if (spi->master->num_chipselect > 1) {
-		struct count_children cc;
-
-		cc.n = 0;
-		cc.bus = spi->dev.bus;
-		status = device_for_each_child(spi->dev.parent, &cc,
-				maybe_count_child);
-		if (status < 0) {
-			dev_err(&spi->dev, "can't share SPI bus\n");
-			return status;
-		}
-
-		dev_warn(&spi->dev, "ASSUMING SPI bus stays unshared!\n");
-	}
-
 	/* We need a supply of ones to transmit.  This is the only time
 	 * the CPU touches these, so cache coherency isn't a concern.
 	 *
-- 
1.6.5.rc1

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