[PATCH v2] spi: bitbang: Replace spinlock by mutex

[Nicolas Boichat]

chipselect (in the case of spi-gpio: spi_gpio_chipselect, which
calls gpiod_set_raw_value_cansleep) can sleep, so we should not
hold a spinlock while calling it from spi_bitbang_setup.

This issue was introduced by this commit, which converted spi-gpio
to cansleep variants:
d9dda5a191 "spi: spi-gpio: Use 'cansleep' variants to access GPIO"

Replacing the lock variable by a mutex fixes the issue: This is
safe as all instances where the lock is used are called from
contexts that can sleep.

Finally, update spi-ppc4xx and and spi-s3c24xx to use mutex
functions, as they directly hold the lock for similar purpose.

Signed-off-by: Nicolas Boichat <drinkcat at chromium.org>
---
Going the "safer" way and just replacing the spinlock by a
mutex.

Applies on top of broonie-sound/for-next, and compile-tested on
x86-64/arm (allyesconfig) and ppc44x (defconfig+SPI driver),
and runtime-tested on an arm platform.

Thanks!

 drivers/spi/spi-bitbang.c       | 17 +++++++----------
 drivers/spi/spi-ppc4xx.c        |  4 ++--
 drivers/spi/spi-s3c24xx.c       |  4 ++--
 include/linux/spi/spi_bitbang.h |  2 +-
 4 files changed, 12 insertions(+), 15 deletions(-)

diff --git a/drivers/spi/spi-bitbang.c b/drivers/spi/spi-bitbang.c
index 840a498..ef43ef5 100644
--- a/drivers/spi/spi-bitbang.c
+++ b/drivers/spi/spi-bitbang.c
@@ -180,7 +180,6 @@ int spi_bitbang_setup(struct spi_device *spi)
 {
 	struct spi_bitbang_cs	*cs = spi->controller_state;
 	struct spi_bitbang	*bitbang;
-	unsigned long		flags;
 
 	bitbang = spi_master_get_devdata(spi->master);
 
@@ -210,12 +209,12 @@ int spi_bitbang_setup(struct spi_device *spi)
 	 */
 
 	/* deselect chip (low or high) */
-	spin_lock_irqsave(&bitbang->lock, flags);
+	mutex_lock(&bitbang->lock);
 	if (!bitbang->busy) {
 		bitbang->chipselect(spi, BITBANG_CS_INACTIVE);
 		ndelay(cs->nsecs);
 	}
-	spin_unlock_irqrestore(&bitbang->lock, flags);
+	mutex_unlock(&bitbang->lock);
 
 	return 0;
 }
@@ -255,13 +254,12 @@ static int spi_bitbang_bufs(struct spi_device *spi, struct spi_transfer *t)
 static int spi_bitbang_prepare_hardware(struct spi_master *spi)
 {
 	struct spi_bitbang	*bitbang;
-	unsigned long		flags;
 
 	bitbang = spi_master_get_devdata(spi);
 
-	spin_lock_irqsave(&bitbang->lock, flags);
+	mutex_lock(&bitbang->lock);
 	bitbang->busy = 1;
-	spin_unlock_irqrestore(&bitbang->lock, flags);
+	mutex_unlock(&bitbang->lock);
 
 	return 0;
 }
@@ -378,13 +376,12 @@ static int spi_bitbang_transfer_one(struct spi_master *master,
 static int spi_bitbang_unprepare_hardware(struct spi_master *spi)
 {
 	struct spi_bitbang	*bitbang;
-	unsigned long		flags;
 
 	bitbang = spi_master_get_devdata(spi);
 
-	spin_lock_irqsave(&bitbang->lock, flags);
+	mutex_lock(&bitbang->lock);
 	bitbang->busy = 0;
-	spin_unlock_irqrestore(&bitbang->lock, flags);
+	mutex_unlock(&bitbang->lock);
 
 	return 0;
 }
@@ -427,7 +424,7 @@ int spi_bitbang_start(struct spi_bitbang *bitbang)
 	if (!master || !bitbang->chipselect)
 		return -EINVAL;
 
-	spin_lock_init(&bitbang->lock);
+	mutex_init(&bitbang->lock);
 
 	if (!master->mode_bits)
 		master->mode_bits = SPI_CPOL | SPI_CPHA | bitbang->flags;
diff --git a/drivers/spi/spi-ppc4xx.c b/drivers/spi/spi-ppc4xx.c
index 54fb984..dd3d0a2 100644
--- a/drivers/spi/spi-ppc4xx.c
+++ b/drivers/spi/spi-ppc4xx.c
@@ -210,12 +210,12 @@ static int spi_ppc4xx_setupxfer(struct spi_device *spi, struct spi_transfer *t)
 	if (in_8(&hw->regs->cdm) != cdm)
 		out_8(&hw->regs->cdm, cdm);
 
-	spin_lock(&hw->bitbang.lock);
+	mutex_lock(&hw->bitbang.lock);
 	if (!hw->bitbang.busy) {
 		hw->bitbang.chipselect(spi, BITBANG_CS_INACTIVE);
 		/* Need to ndelay here? */
 	}
-	spin_unlock(&hw->bitbang.lock);
+	mutex_unlock(&hw->bitbang.lock);
 
 	return 0;
 }
diff --git a/drivers/spi/spi-s3c24xx.c b/drivers/spi/spi-s3c24xx.c
index f36bc32..4e7d1bf 100644
--- a/drivers/spi/spi-s3c24xx.c
+++ b/drivers/spi/spi-s3c24xx.c
@@ -198,12 +198,12 @@ static int s3c24xx_spi_setup(struct spi_device *spi)
 	if (ret)
 		return ret;
 
-	spin_lock(&hw->bitbang.lock);
+	mutex_lock(&hw->bitbang.lock);
 	if (!hw->bitbang.busy) {
 		hw->bitbang.chipselect(spi, BITBANG_CS_INACTIVE);
 		/* need to ndelay for 0.5 clocktick ? */
 	}
-	spin_unlock(&hw->bitbang.lock);
+	mutex_unlock(&hw->bitbang.lock);
 
 	return 0;
 }
diff --git a/include/linux/spi/spi_bitbang.h b/include/linux/spi/spi_bitbang.h
index 85578d4..154788e 100644
--- a/include/linux/spi/spi_bitbang.h
+++ b/include/linux/spi/spi_bitbang.h
@@ -4,7 +4,7 @@
 #include <linux/workqueue.h>
 
 struct spi_bitbang {
-	spinlock_t		lock;
+	struct mutex		lock;
 	u8			busy;
 	u8			use_dma;
 	u8			flags;		/* extra spi->mode support */
-- 
2.5.0.276.gf5e568e