From 3843384a055496dfed3c93ae883d964d8290fdab Mon Sep 17 00:00:00 2001 From: Oskar Schirmer Date: Thu, 13 May 2010 00:42:23 -0700 Subject: [PATCH] Input: ad7877 - keep dma rx buffers in seperate cache lines MIME-Version: 1.0 Content-Type: text/plain; charset=utf8 Content-Transfer-Encoding: 8bit With dma based spi transmission, data corruption is observed occasionally. With dma buffers located right next to msg and xfer fields, cache lines correctly flushed in preparation for dma usage may be polluted again when writing to fields in the same cache line. Make sure cache fields used with dma do not share cache lines with fields changed during dma handling. As both fields are part of a struct that is allocated via kzalloc, thus cache aligned, moving the fields to the 1st position and insert padding for alignment does the job. Signed-off-by: Oskar Schirmer Signed-off-by: Daniel Glöckner Signed-off-by: Oliver Schneidewind Signed-off-by: Johannes Weiner Acked-by: Mike Frysinger [dtor@mail.ru - changed to use ___cacheline_aligned as suggested by akpm] Signed-off-by: Dmitry Torokhov --- drivers/input/touchscreen/ad7877.c | 15 ++++++++++++--- 1 file changed, 12 insertions(+), 3 deletions(-) diff --git a/drivers/input/touchscreen/ad7877.c b/drivers/input/touchscreen/ad7877.c index e019d53d..0d2d7e5 100644 --- a/drivers/input/touchscreen/ad7877.c +++ b/drivers/input/touchscreen/ad7877.c @@ -156,9 +156,14 @@ struct ser_req { u16 reset; u16 ref_on; u16 command; - u16 sample; struct spi_message msg; struct spi_transfer xfer[6]; + + /* + * DMA (thus cache coherency maintenance) requires the + * transfer buffers to live in their own cache lines. + */ + u16 sample ____cacheline_aligned; }; struct ad7877 { @@ -182,8 +187,6 @@ struct ad7877 { u8 averaging; u8 pen_down_acc_interval; - u16 conversion_data[AD7877_NR_SENSE]; - struct spi_transfer xfer[AD7877_NR_SENSE + 2]; struct spi_message msg; @@ -195,6 +198,12 @@ struct ad7877 { spinlock_t lock; struct timer_list timer; /* P: lock */ unsigned pending:1; /* P: lock */ + + /* + * DMA (thus cache coherency maintenance) requires the + * transfer buffers to live in their own cache lines. + */ + u16 conversion_data[AD7877_NR_SENSE] ____cacheline_aligned; }; static int gpio3; -- 2.7.4