[PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[kernel-TqfNSX0MhmxHKSADF0wUEw]

From: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>

This resulted in the use of polling mode when other approaches
(dma or interrupts) would have been more appropriate.

Happened for transfers longer than 477 bytes.

Reported-by: Noralf Tronnes <noralf-L59+Z2yzLopAfugRpC6u6w@public.gmane.org>
Signed-off-by: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
---
 drivers/spi/spi-bcm2835.c |   10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index c9357bb..e7874a6 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -480,7 +480,7 @@ static int bcm2835_spi_transfer_one_poll(struct spi_master *master,
 					 struct spi_device *spi,
 					 struct spi_transfer *tfr,
 					 u32 cs,
-					 unsigned long xfer_time_us)
+					 unsigned long long xfer_time_us)
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long timeout;
@@ -531,7 +531,8 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long spi_hz, clk_hz, cdiv;
-	unsigned long spi_used_hz, xfer_time_us;
+	unsigned long spi_used_hz;
+	unsigned long long xfer_time_us;
 	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
 
 	/* set clock */
@@ -573,9 +574,10 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 	bs->rx_len = tfr->len;
 
 	/* calculate the estimated time in us the transfer runs */
-	xfer_time_us = tfr->len
+	xfer_time_us = (unsigned long long)tfr->len
 		* 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */
-		* 1000000 / spi_used_hz;
+		* 1000000;
+	do_div(xfer_time_us, spi_used_hz);
 
 	/* for short requests run polling*/
 	if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US)
-- 
1.7.10.4

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Re: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[Mark Brown]

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On Wed, Jul 29, 2015 at 07:34:10AM +0000, kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org wrote:
> From: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
> 
> This resulted in the use of polling mode when other approaches
> (dma or interrupts) would have been more appropriate.

Please describe the actual issue and how it's being fixed in the commit
message.  In this case the fix appears to be converting the timeout
variable to a long long which will make things better but obviously
isn't a complete fix for overflows - presumably the ideal thing here is
to handle saturation better?

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Re: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[Martin Sperl]

> On 29.07.2015, at 16:03, Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org> wrote:
> 
> On Wed, Jul 29, 2015 at 07:34:10AM +0000, kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org wrote:
>> From: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
>> 
>> This resulted in the use of polling mode when other approaches
>> (dma or interrupts) would have been more appropriate.
> 
> Please describe the actual issue and how it's being fixed in the commit
> message.  In this case the fix appears to be converting the timeout
> variable to a long long which will make things better but obviously
> isn't a complete fix for overflows - presumably the ideal thing here is
> to handle saturation better?

Will change the description of the commit and resubmit.

As for saturation I guess that nobody will ever run a spi-transfer
of len=2049638230413 bytes (at which point it would wrap) which:

a) would take 4679 days to reach at 125MHz 
  (the max frequency of the bcm2835 SPI HW limit)
b) would not fit spi_transfer->len (defined as unsigned)

So handling saturation is not an issue when using "long long”
in the context of this device.

Martin--
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Re: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[Martin Sperl]

Hi Mark!

> On 29.07.2015, at 16:31, Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org> wrote:
> 
> Will change the description of the commit and resubmit.

Now that you have applied the patch already, do I need to
resubmit the commit with a changed description?

Martin
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Re: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

[Mark Brown]

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On Wed, Jul 29, 2015 at 04:35:03PM +0200, Martin Sperl wrote:

> Now that you have applied the patch already, do I need to
> resubmit the commit with a changed description?

No, it's fine.

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Applied "spi: bcm2835: fix overflow in calculation of transfer time" to the spi tree

[Mark Brown]

The patch

   spi: bcm2835: fix overflow in calculation of transfer time

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From c020e378b2b388b712a40dce2da6d437d2b6e0e0 Mon Sep 17 00:00:00 2001
From: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
Date: Wed, 29 Jul 2015 07:34:10 +0000
Subject: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

This resulted in the use of polling mode when other approaches
(dma or interrupts) would have been more appropriate.

Happened for transfers longer than 477 bytes.

Reported-by: Noralf Tronnes <noralf-L59+Z2yzLopAfugRpC6u6w@public.gmane.org>
Signed-off-by: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
Signed-off-by: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 drivers/spi/spi-bcm2835.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index 59705ab..767aa00 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -480,7 +480,7 @@ static int bcm2835_spi_transfer_one_poll(struct spi_master *master,
 					 struct spi_device *spi,
 					 struct spi_transfer *tfr,
 					 u32 cs,
-					 unsigned long xfer_time_us)
+					 unsigned long long xfer_time_us)
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long timeout;
@@ -531,7 +531,8 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long spi_hz, clk_hz, cdiv;
-	unsigned long spi_used_hz, xfer_time_us;
+	unsigned long spi_used_hz;
+	unsigned long long xfer_time_us;
 	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
 
 	/* set clock */
@@ -575,9 +576,10 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 	bs->rx_len = tfr->len;
 
 	/* calculate the estimated time in us the transfer runs */
-	xfer_time_us = tfr->len
+	xfer_time_us = (unsigned long long)tfr->len
 		* 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */
-		* 1000000 / spi_used_hz;
+		* 1000000;
+	do_div(xfer_time_us, spi_used_hz);
 
 	/* for short requests run polling*/
 	if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US)
-- 
2.1.4

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Applied "spi: bcm2835: fix overflow in calculation of transfer time" to the spi tree

[Mark Brown]

The patch

   spi: bcm2835: fix overflow in calculation of transfer time

has been applied to the spi tree at

   git://git.kernel.org/pub/scm/linux/kernel/git/broonie/spi.git 

All being well this means that it will be integrated into the linux-next
tree (usually sometime in the next 24 hours) and sent to Linus during
the next merge window (or sooner if it is a bug fix), however if
problems are discovered then the patch may be dropped or reverted.  

You may get further e-mails resulting from automated or manual testing
and review of the tree, please engage with people reporting problems and
send followup patches addressing any issues that are reported if needed.

If any updates are required or you are submitting further changes they
should be sent as incremental updates against current git, existing
patches will not be replaced.

Please add any relevant lists and maintainers to the CCs when replying
to this mail.

Thanks,
Mark

>From 0122a5183088e3117bb9c8fbe248914efb502f3f Mon Sep 17 00:00:00 2001
From: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
Date: Wed, 29 Jul 2015 07:34:10 +0000
Subject: [PATCH] spi: bcm2835: fix overflow in calculation of transfer time

This resulted in the use of polling mode when other approaches
(dma or interrupts) would have been more appropriate.

Happened for transfers longer than 477 bytes.

Reported-by: Noralf Tronnes <noralf-L59+Z2yzLopAfugRpC6u6w@public.gmane.org>
Signed-off-by: Martin Sperl <kernel-TqfNSX0MhmxHKSADF0wUEw@public.gmane.org>
Signed-off-by: Mark Brown <broonie-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
---
 drivers/spi/spi-bcm2835.c | 10 ++++++----
 1 file changed, 6 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi-bcm2835.c b/drivers/spi/spi-bcm2835.c
index c9357bb..e7874a6 100644
--- a/drivers/spi/spi-bcm2835.c
+++ b/drivers/spi/spi-bcm2835.c
@@ -480,7 +480,7 @@ static int bcm2835_spi_transfer_one_poll(struct spi_master *master,
 					 struct spi_device *spi,
 					 struct spi_transfer *tfr,
 					 u32 cs,
-					 unsigned long xfer_time_us)
+					 unsigned long long xfer_time_us)
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long timeout;
@@ -531,7 +531,8 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 {
 	struct bcm2835_spi *bs = spi_master_get_devdata(master);
 	unsigned long spi_hz, clk_hz, cdiv;
-	unsigned long spi_used_hz, xfer_time_us;
+	unsigned long spi_used_hz;
+	unsigned long long xfer_time_us;
 	u32 cs = bcm2835_rd(bs, BCM2835_SPI_CS);
 
 	/* set clock */
@@ -573,9 +574,10 @@ static int bcm2835_spi_transfer_one(struct spi_master *master,
 	bs->rx_len = tfr->len;
 
 	/* calculate the estimated time in us the transfer runs */
-	xfer_time_us = tfr->len
+	xfer_time_us = (unsigned long long)tfr->len
 		* 9 /* clocks/byte - SPI-HW waits 1 clock after each byte */
-		* 1000000 / spi_used_hz;
+		* 1000000;
+	do_div(xfer_time_us, spi_used_hz);
 
 	/* for short requests run polling*/
 	if (xfer_time_us <= BCM2835_SPI_POLLING_LIMIT_US)
-- 
2.5.0

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