[PATCH] spi: spidev: Use separate TX and RX bounce buffers

[PATCH] spi: spidev: Use separate TX and RX bounce buffers

[Ray Jui]

By using separate TX and RX bounce buffers, we avoid potential cache
flush and invalidation sequence issue that may be encountered when a
single bounce buffer is shared between TX and RX

Signed-off-by: Ray Jui <rjui@broadcom.com>
Reviewed-by: JD (Jiandong) Zheng <jdzheng@broadcom.com>
---
 drivers/spi/spidev.c |   79 +++++++++++++++++++++++++++++++++-----------------
 1 file changed, 52 insertions(+), 27 deletions(-)

diff --git a/drivers/spi/spidev.c b/drivers/spi/spidev.c
index e3bc23b..e50039f 100644
--- a/drivers/spi/spidev.c
+++ b/drivers/spi/spidev.c
@@ -82,10 +82,11 @@ struct spidev_data {
 	struct spi_device	*spi;
 	struct list_head	device_entry;
 
-	/* buffer is NULL unless this device is open (users > 0) */
+	/* TX/RX buffers are NULL unless this device is open (users > 0) */
 	struct mutex		buf_lock;
 	unsigned		users;
-	u8			*buffer;
+	u8			*tx_buffer;
+	u8			*rx_buffer;
 };
 
 static LIST_HEAD(device_list);
@@ -135,7 +136,7 @@ static inline ssize_t
 spidev_sync_write(struct spidev_data *spidev, size_t len)
 {
 	struct spi_transfer	t = {
-			.tx_buf		= spidev->buffer,
+			.tx_buf		= spidev->tx_buffer,
 			.len		= len,
 		};
 	struct spi_message	m;
@@ -149,7 +150,7 @@ static inline ssize_t
 spidev_sync_read(struct spidev_data *spidev, size_t len)
 {
 	struct spi_transfer	t = {
-			.rx_buf		= spidev->buffer,
+			.rx_buf		= spidev->rx_buffer,
 			.len		= len,
 		};
 	struct spi_message	m;
@@ -179,7 +180,7 @@ spidev_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
 	if (status > 0) {
 		unsigned long	missing;
 
-		missing = copy_to_user(buf, spidev->buffer, status);
+		missing = copy_to_user(buf, spidev->rx_buffer, status);
 		if (missing == status)
 			status = -EFAULT;
 		else
@@ -206,7 +207,7 @@ spidev_write(struct file *filp, const char __user *buf,
 	spidev = filp->private_data;
 
 	mutex_lock(&spidev->buf_lock);
-	missing = copy_from_user(spidev->buffer, buf, count);
+	missing = copy_from_user(spidev->tx_buffer, buf, count);
 	if (missing == 0)
 		status = spidev_sync_write(spidev, count);
 	else
@@ -224,7 +225,7 @@ static int spidev_message(struct spidev_data *spidev,
 	struct spi_transfer	*k_tmp;
 	struct spi_ioc_transfer *u_tmp;
 	unsigned		n, total;
-	u8			*buf;
+	u8			*tx_buf, *rx_buf;
 	int			status = -EFAULT;
 
 	spi_message_init(&msg);
@@ -236,7 +237,8 @@ static int spidev_message(struct spidev_data *spidev,
 	 * We walk the array of user-provided transfers, using each one
 	 * to initialize a kernel version of the same transfer.
 	 */
-	buf = spidev->buffer;
+	tx_buf = spidev->tx_buffer;
+	rx_buf = spidev->rx_buffer;
 	total = 0;
 	for (n = n_xfers, k_tmp = k_xfers, u_tmp = u_xfers;
 			n;
@@ -250,20 +252,21 @@ static int spidev_message(struct spidev_data *spidev,
 		}
 
 		if (u_tmp->rx_buf) {
-			k_tmp->rx_buf = buf;
+			k_tmp->rx_buf = rx_buf;
 			if (!access_ok(VERIFY_WRITE, (u8 __user *)
 						(uintptr_t) u_tmp->rx_buf,
 						u_tmp->len))
 				goto done;
 		}
 		if (u_tmp->tx_buf) {
-			k_tmp->tx_buf = buf;
-			if (copy_from_user(buf, (const u8 __user *)
+			k_tmp->tx_buf = tx_buf;
+			if (copy_from_user(tx_buf, (const u8 __user *)
 						(uintptr_t) u_tmp->tx_buf,
 					u_tmp->len))
 				goto done;
 		}
-		buf += k_tmp->len;
+		tx_buf += k_tmp->len;
+		rx_buf += k_tmp->len;
 
 		k_tmp->cs_change = !!u_tmp->cs_change;
 		k_tmp->tx_nbits = u_tmp->tx_nbits;
@@ -290,17 +293,17 @@ static int spidev_message(struct spidev_data *spidev,
 		goto done;
 
 	/* copy any rx data out of bounce buffer */
-	buf = spidev->buffer;
+	rx_buf = spidev->rx_buffer;
 	for (n = n_xfers, u_tmp = u_xfers; n; n--, u_tmp++) {
 		if (u_tmp->rx_buf) {
 			if (__copy_to_user((u8 __user *)
-					(uintptr_t) u_tmp->rx_buf, buf,
+					(uintptr_t) u_tmp->rx_buf, rx_buf,
 					u_tmp->len)) {
 				status = -EFAULT;
 				goto done;
 			}
 		}
-		buf += u_tmp->len;
+		rx_buf += u_tmp->len;
 	}
 	status = total;
 
@@ -508,22 +511,41 @@ static int spidev_open(struct inode *inode, struct file *filp)
 			break;
 		}
 	}
-	if (status == 0) {
-		if (!spidev->buffer) {
-			spidev->buffer = kmalloc(bufsiz, GFP_KERNEL);
-			if (!spidev->buffer) {
+
+	if (status) {
+		pr_debug("spidev: nothing for minor %d\n", iminor(inode));
+		goto err_find_dev;
+	}
+
+	if (!spidev->tx_buffer) {
+		spidev->tx_buffer = kmalloc(bufsiz, GFP_KERNEL);
+		if (!spidev->tx_buffer) {
 				dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
 				status = -ENOMEM;
+			goto err_find_dev;
 			}
 		}
-		if (status == 0) {
-			spidev->users++;
-			filp->private_data = spidev;
-			nonseekable_open(inode, filp);
+
+	if (!spidev->rx_buffer) {
+		spidev->rx_buffer = kmalloc(bufsiz, GFP_KERNEL);
+		if (!spidev->rx_buffer) {
+			dev_dbg(&spidev->spi->dev, "open/ENOMEM\n");
+			status = -ENOMEM;
+			goto err_alloc_rx_buf;
 		}
-	} else
-		pr_debug("spidev: nothing for minor %d\n", iminor(inode));
+	}
+
+	spidev->users++;
+	filp->private_data = spidev;
+	nonseekable_open(inode, filp);
+
+	mutex_unlock(&device_list_lock);
+	return 0;
 
+err_alloc_rx_buf:
+	kfree(spidev->tx_buffer);
+	spidev->tx_buffer = NULL;
+err_find_dev:
 	mutex_unlock(&device_list_lock);
 	return status;
 }
@@ -542,8 +564,11 @@ static int spidev_release(struct inode *inode, struct file *filp)
 	if (!spidev->users) {
 		int		dofree;
 
-		kfree(spidev->buffer);
-		spidev->buffer = NULL;
+		kfree(spidev->tx_buffer);
+		spidev->tx_buffer = NULL;
+
+		kfree(spidev->rx_buffer);
+		spidev->rx_buffer = NULL;
 
 		/* ... after we unbound from the underlying device? */
 		spin_lock_irq(&spidev->spi_lock);
-- 
1.7.9.5

Re: [PATCH] spi: spidev: Use separate TX and RX bounce buffers

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 268 bytes --]

On Thu, Oct 09, 2014 at 11:19:25AM -0700, Ray Jui wrote:
> By using separate TX and RX bounce buffers, we avoid potential cache
> flush and invalidation sequence issue that may be encountered when a
> single bounce buffer is shared between TX and RX

Applied, thanks.

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Re: [PATCH] spi: spidev: Use separate TX and RX bounce buffers

[Ray Jui]

On 10/13/2014 4:07 AM, Mark Brown wrote:
> On Thu, Oct 09, 2014 at 11:19:25AM -0700, Ray Jui wrote:
>> By using separate TX and RX bounce buffers, we avoid potential cache
>> flush and invalidation sequence issue that may be encountered when a
>> single bounce buffer is shared between TX and RX
>
> Applied, thanks.
>
Thanks, Mark.
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[PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Ray Jui]

The PL022 SPI driver maps the DMA RX buffer before the DMA TX buffer. In
most cases, the sequence of the mapping does not matter. But in cases
where TX and RX happen to use the same buffer, e.g., spidev, it causes
the cached TX data not written to memory, because the same memory has
been marked invalid when dma_map_sg on the RX buffer is called

The solution is to reverse the sequence so it maps the TX buffer before
the RX buffer

Signed-off-by: Ray Jui <rjui-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
Reviewed-by: JD (Jiandong) Zheng <jdzheng-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
Tested-by: Scott Branden <sbranden-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
Reviewed-by: Scott Branden <sbranden-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
---
 drivers/spi/spi-pl022.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/drivers/spi/spi-pl022.c b/drivers/spi/spi-pl022.c
index 1189cfd..edb7298 100644
--- a/drivers/spi/spi-pl022.c
+++ b/drivers/spi/spi-pl022.c
@@ -773,10 +773,10 @@ static void *next_transfer(struct pl022 *pl022)
 static void unmap_free_dma_scatter(struct pl022 *pl022)
 {
 	/* Unmap and free the SG tables */
-	dma_unmap_sg(pl022->dma_tx_channel->device->dev, pl022->sgt_tx.sgl,
-		     pl022->sgt_tx.nents, DMA_TO_DEVICE);
 	dma_unmap_sg(pl022->dma_rx_channel->device->dev, pl022->sgt_rx.sgl,
 		     pl022->sgt_rx.nents, DMA_FROM_DEVICE);
+	dma_unmap_sg(pl022->dma_tx_channel->device->dev, pl022->sgt_tx.sgl,
+		     pl022->sgt_tx.nents, DMA_TO_DEVICE);
 	sg_free_table(&pl022->sgt_rx);
 	sg_free_table(&pl022->sgt_tx);
 }
@@ -1026,16 +1026,16 @@ static int configure_dma(struct pl022 *pl022)
 			  pl022->cur_transfer->len, &pl022->sgt_tx);
 
 	/* Map DMA buffers */
-	rx_sglen = dma_map_sg(rxchan->device->dev, pl022->sgt_rx.sgl,
-			   pl022->sgt_rx.nents, DMA_FROM_DEVICE);
-	if (!rx_sglen)
-		goto err_rx_sgmap;
-
 	tx_sglen = dma_map_sg(txchan->device->dev, pl022->sgt_tx.sgl,
 			   pl022->sgt_tx.nents, DMA_TO_DEVICE);
 	if (!tx_sglen)
 		goto err_tx_sgmap;
 
+	rx_sglen = dma_map_sg(rxchan->device->dev, pl022->sgt_rx.sgl,
+			   pl022->sgt_rx.nents, DMA_FROM_DEVICE);
+	if (!rx_sglen)
+		goto err_rx_sgmap;
+
 	/* Send both scatterlists */
 	rxdesc = dmaengine_prep_slave_sg(rxchan,
 				      pl022->sgt_rx.sgl,
@@ -1070,12 +1070,12 @@ err_txdesc:
 	dmaengine_terminate_all(txchan);
 err_rxdesc:
 	dmaengine_terminate_all(rxchan);
+	dma_unmap_sg(rxchan->device->dev, pl022->sgt_rx.sgl,
+		     pl022->sgt_rx.nents, DMA_FROM_DEVICE);
+err_rx_sgmap:
 	dma_unmap_sg(txchan->device->dev, pl022->sgt_tx.sgl,
 		     pl022->sgt_tx.nents, DMA_TO_DEVICE);
 err_tx_sgmap:
-	dma_unmap_sg(rxchan->device->dev, pl022->sgt_rx.sgl,
-		     pl022->sgt_tx.nents, DMA_FROM_DEVICE);
-err_rx_sgmap:
 	sg_free_table(&pl022->sgt_tx);
 err_alloc_tx_sg:
 	sg_free_table(&pl022->sgt_rx);
-- 
1.7.9.5

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Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 623 bytes --]

On Tue, Oct 07, 2014 at 09:38:47PM -0700, Ray Jui wrote:

> The PL022 SPI driver maps the DMA RX buffer before the DMA TX buffer. In
> most cases, the sequence of the mapping does not matter. But in cases
> where TX and RX happen to use the same buffer, e.g., spidev, it causes
> the cached TX data not written to memory, because the same memory has
> been marked invalid when dma_map_sg on the RX buffer is called

This seems like it is a bug in spidev, using the same buffer simultaneously
for both directions isn't something I'd think would be expected to work
reliably unless it was explicitly mapped as bidirectional.

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Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Ray Jui]

On 10/8/2014 4:21 AM, Mark Brown wrote:
> On Tue, Oct 07, 2014 at 09:38:47PM -0700, Ray Jui wrote:
>
>> The PL022 SPI driver maps the DMA RX buffer before the DMA TX buffer. In
>> most cases, the sequence of the mapping does not matter. But in cases
>> where TX and RX happen to use the same buffer, e.g., spidev, it causes
>> the cached TX data not written to memory, because the same memory has
>> been marked invalid when dma_map_sg on the RX buffer is called
>
> This seems like it is a bug in spidev, using the same buffer simultaneously
> for both directions isn't something I'd think would be expected to work
> reliably unless it was explicitly mapped as bidirectional.
>
Hi Mark,

Thanks for the reply. It looks like you are also the maintainer of 
spidev. In this case, could you please help to confirm that you expect 
spidev to use separate buffers for TX and RX? If so, I can go ahead and 
make the change in spidev.

+ Grant

Thanks,

Ray

Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 481 bytes --]

On Wed, Oct 08, 2014 at 09:14:35AM -0700, Ray Jui wrote:

> Thanks for the reply. It looks like you are also the maintainer of spidev.
> In this case, could you please help to confirm that you expect spidev to use
> separate buffers for TX and RX? If so, I can go ahead and make the change in
> spidev.

Yes, that would be my expectation for maximum robustness (or if it is
going to use one buffer it explicitly maps it for mixed use but I'd
expect that to be asking for trouble).

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Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Ray Jui]

On 10/8/2014 11:21 AM, Mark Brown wrote:
> On Wed, Oct 08, 2014 at 09:14:35AM -0700, Ray Jui wrote:
>
>> Thanks for the reply. It looks like you are also the maintainer of spidev.
>> In this case, could you please help to confirm that you expect spidev to use
>> separate buffers for TX and RX? If so, I can go ahead and make the change in
>> spidev.
>
> Yes, that would be my expectation for maximum robustness (or if it is
> going to use one buffer it explicitly maps it for mixed use but I'd
> expect that to be asking for trouble).
>
Okay, Mark. I'm going to make the change in the spidev and submit a new 
patch.

Thanks for the feedback.

Ray
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Re: [PATCH] spi: pl022: Fix broken spidev when DMA is enabled

[Geert Uytterhoeven]

On Wed, Oct 8, 2014 at 8:21 PM, Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> On Wed, Oct 08, 2014 at 09:14:35AM -0700, Ray Jui wrote:
>> Thanks for the reply. It looks like you are also the maintainer of spidev.
>> In this case, could you please help to confirm that you expect spidev to use
>> separate buffers for TX and RX? If so, I can go ahead and make the change in
>> spidev.
>
> Yes, that would be my expectation for maximum robustness (or if it is
> going to use one buffer it explicitly maps it for mixed use but I'd
> expect that to be asking for trouble).

Having two separate buffers avoids false successes when running
"spidev_test --loop" on a buggy SPI master driver.
Been there, done that ;-)

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert-Td1EMuHUCqxL1ZNQvxDV9g@public.gmane.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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[PATCH] spi: pl022: Fix incorrect dma_unmap_sg

[Ray Jui]

When mapped RX DMA entries are unmapped in an error condition when DMA
is firstly configured in the driver, the number of TX DMA entries was
passed in, which is incorrect

Signed-off-by: Ray Jui <rjui-dY08KVG/lbpWk0Htik3J/w@public.gmane.org>
---
 drivers/spi/spi-pl022.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/spi/spi-pl022.c b/drivers/spi/spi-pl022.c
index f35f723..fc2dd84 100644
--- a/drivers/spi/spi-pl022.c
+++ b/drivers/spi/spi-pl022.c
@@ -1106,7 +1106,7 @@ err_rxdesc:
 		     pl022->sgt_tx.nents, DMA_TO_DEVICE);
 err_tx_sgmap:
 	dma_unmap_sg(rxchan->device->dev, pl022->sgt_rx.sgl,
-		     pl022->sgt_tx.nents, DMA_FROM_DEVICE);
+		     pl022->sgt_rx.nents, DMA_FROM_DEVICE);
 err_rx_sgmap:
 	sg_free_table(&pl022->sgt_tx);
 err_alloc_tx_sg:
-- 
1.7.9.5

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Re: [PATCH] spi: pl022: Fix incorrect dma_unmap_sg

[Mark Brown]

[-- Attachment #1: Type: text/plain, Size: 252 bytes --]

On Thu, Oct 09, 2014 at 11:44:54AM -0700, Ray Jui wrote:
> When mapped RX DMA entries are unmapped in an error condition when DMA
> is firstly configured in the driver, the number of TX DMA entries was
> passed in, which is incorrect

Applied, thanks.

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Re: [PATCH] spi: pl022: Fix incorrect dma_unmap_sg

[Ray Jui]

On 10/13/2014 4:08 AM, Mark Brown wrote:
> On Thu, Oct 09, 2014 at 11:44:54AM -0700, Ray Jui wrote:
>> When mapped RX DMA entries are unmapped in an error condition when DMA
>> is firstly configured in the driver, the number of TX DMA entries was
>> passed in, which is incorrect
>
> Applied, thanks.
>
Thanks, Mark.
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