The patch titled
spi: spi_write_then_read() regression fix
has been added to the -mm tree. Its filename is
spi-spi_write_then_read-regression-fix.patch
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------------------------------------------------------
Subject: spi: spi_write_then_read() regression fix
From: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
The recent "simplify spi_write_then_read()" patch included a small
regression from the 2.6.27 behavior with its performance win.
All SPI transfers are full duplex, and are packaged as half duplex
by either discarding the data that's read ("write only"), or else
by writing zeroes ("read only"). That patch wasn't ensuring that
zeroes were getting written out during the "half duplex read" part
of the transaction; instead, old RX bits were getting sent.
The fix is trivial: zero the buffer before using it.
Signed-off-by: David Brownell <dbrownell@xxxxxxxxxxxxxxxxxxxxx>
Cc: Vernon Sauder <vernoninhand@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
drivers/spi/spi.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)
diff -puN drivers/spi/spi.c~spi-spi_write_then_read-regression-fix drivers/spi/spi.c
--- a/drivers/spi/spi.c~spi-spi_write_then_read-regression-fix
+++ a/drivers/spi/spi.c
@@ -677,11 +677,13 @@ int spi_write_then_read(struct spi_devic
/* ... unless someone else is using the pre-allocated buffer */
if (!mutex_trylock(&lock)) {
- local_buf = kmalloc(SPI_BUFSIZ, GFP_KERNEL);
+ local_buf = kzalloc(SPI_BUFSIZ, GFP_KERNEL);
if (!local_buf)
return -ENOMEM;
- } else
+ } else {
local_buf = buf;
+ memset(local_buf, 0, x.len);
+ }
memcpy(local_buf, txbuf, n_tx);
x.tx_buf = local_buf;
_
Patches currently in -mm which might be from dbrownell@xxxxxxxxxxxxxxxxxxxxx are
spi-spi_write_then_read-regression-fix.patch
linux-next.patch
acpi-fix-acpi_fadt_s4_rtc_wake-comment.patch
documentation-when-to-bug-and-when-to-not-bug.patch
spi_gpio-driver.patch
spi_gpio-driver-cleanups.patch
atmel_spi-clean-up-spiv1-quirk-handling.patch
spi-atmel_spi-update-chipselect-handling.patch
spi-use-generic-gpio-calls-in-spi_s3c24xx_gpio.patch
drivers-spi-move-a-dereference-below-a-null-test.patch
mfd-da903x-section-fix.patch
rtc-ds1307-remove-legacy-probe-checks.patch
rtc-bunch-of-drivers-fix-no-irq-case-handing.patch
twl4030-gpio-cleanup-debounce.patch
gpio-pca953x-handles-more-chips-i2c-fault-codes.patch
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