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    Subject[PATCH 4.19 12/57] spi: bcm2835aux: fix corruptions for longer spi transfers
    Date
    [ Upstream commit 73b114ee7db1750c0b535199fae383b109bd61d0 ]

    On long running tests with a mcp2517fd can controller it showed that
    on rare occations the data read shows corruptions for longer spi transfers.

    Example of a 22 byte transfer:

    expected (as captured on logic analyzer):
    FF FF 78 00 00 00 08 06 00 00 91 20 77 56 84 85 86 87 88 89 8a 8b

    read by the driver:
    FF FF 78 00 00 00 08 06 00 00 91 20 77 56 84 88 89 8a 00 00 8b 9b

    To fix this use BCM2835_AUX_SPI_STAT_RX_LVL to determine when we may
    read data from the fifo reliably without any corruption.

    Surprisingly the only values ever empirically read in
    BCM2835_AUX_SPI_STAT_RX_LVL are 0x00, 0x10, 0x20 and 0x30.
    So whenever the mask is not 0 we can read from the fifo in a safe manner.

    The patch has now been tested intensively and we are no longer
    able to reproduce the "RX" issue any longer.

    Fixes: 1ea29b39f4c812ec ("spi: bcm2835aux: add bcm2835 auxiliary spi device...")
    Reported-by: Hubert Denkmair <h.denkmair@intence.de>
    Signed-off-by: Martin Sperl <kernel@martin.sperl.org>
    Acked-by: Stefan Wahren <stefan.wahren@i2se.com>
    Signed-off-by: Mark Brown <broonie@kernel.org>
    Signed-off-by: Sasha Levin <sashal@kernel.org>
    ---
    drivers/spi/spi-bcm2835aux.c | 8 ++++----
    1 file changed, 4 insertions(+), 4 deletions(-)

    diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
    index b4217f9480014..12c1fa5b06c5b 100644
    --- a/drivers/spi/spi-bcm2835aux.c
    +++ b/drivers/spi/spi-bcm2835aux.c
    @@ -180,12 +180,12 @@ static void bcm2835aux_spi_reset_hw(struct bcm2835aux_spi *bs)

    static void bcm2835aux_spi_transfer_helper(struct bcm2835aux_spi *bs)
    {
    + u32 stat = bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT);
    +
    /* check if we have data to read */
    - while (bs->rx_len &&
    - (!(bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT) &
    - BCM2835_AUX_SPI_STAT_RX_EMPTY))) {
    + for (; bs->rx_len && (stat & BCM2835_AUX_SPI_STAT_RX_LVL);
    + stat = bcm2835aux_rd(bs, BCM2835_AUX_SPI_STAT))
    bcm2835aux_rd_fifo(bs);
    - }

    /* check if we have data to write */
    while (bs->tx_len &&
    --
    2.20.1


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