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    SubjectRe: [PATCH v3] ad7877: keep dma rx buffers in seperate cache lines
    On Mon, May 10, 2010 at 23:05:47 -0700, Dmitry Torokhov wrote:
    > OK, then I have the following which I will apply unless someone shouts.

    Looks good, we tested it on G45, works fine.

    Oskar


    > --
    > Dmitry
    >
    > Input: ad7877 - keep dma rx buffers in seperate cache lines
    >
    > From: Oskar Schirmer <os@emlix.com>
    >
    > 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 <os@emlix.com>
    > Signed-off-by: Daniel Glöckner <dg@emlix.com>
    > Signed-off-by: Oliver Schneidewind <osw@emlix.com>
    > Signed-off-by: Johannes Weiner <jw@emlix.com>
    > Acked-by: Mike Frysinger <vapier@gentoo.org>
    > [dtor@mail.ru - changed to use ___cacheline_aligned at suggestion
    > of akpm]
    > Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
    > ---
    >
    > drivers/input/touchscreen/ad7877.c | 15 ++++++++++++---
    > 1 files changed, 12 insertions(+), 3 deletions(-)
    >
    >
    > diff --git a/drivers/input/touchscreen/ad7877.c b/drivers/input/touchscreen/ad7877.c
    > index e019d53..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;
    >
    >

    --
    oskar schirmer, emlix gmbh, http://www.emlix.com
    fon +49 551 30664-0, fax -11, bahnhofsallee 1b, 37081 göttingen, germany
    sitz der gesellschaft: göttingen, amtsgericht göttingen hr b 3160
    geschäftsführer: dr. uwe kracke, ust-idnr.: de 205 198 055

    emlix - your embedded linux partner
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