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    Subject[PATCH 4.19 289/639] spi: bcm2835aux: fix driver to not allow 65535 (=-1) cs-gpios
    Date
    From: Martin Sperl <kernel@martin.sperl.org>

    [ Upstream commit 509c583620e9053e43d611bf1614fc3d3abafa96 ]

    The original driver by default defines num_chipselects as -1.
    This actually allicates an array of 65535 entries in
    of_spi_register_master.

    There is a side-effect for buggy device trees that (contrary to
    dt-binding documentation) have no cs-gpio defined.

    This mode was never supported by the driver due to limitations
    of native cs and additional code complexity and is explicitly
    not stated to be implemented.

    To keep backwards compatibility with such buggy DTs we limit
    the number of chip_selects to 1, as for all practical purposes
    it is only ever realistic to use a single chip select in
    native cs mode without negative side-effects.

    Fixes: 1ea29b39f4c812ec ("spi: bcm2835aux: add bcm2835 auxiliary spi device...")
    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 | 13 ++++++++++++-
    1 file changed, 12 insertions(+), 1 deletion(-)

    diff --git a/drivers/spi/spi-bcm2835aux.c b/drivers/spi/spi-bcm2835aux.c
    index 12c1fa5b06c5b..c63ed402cf860 100644
    --- a/drivers/spi/spi-bcm2835aux.c
    +++ b/drivers/spi/spi-bcm2835aux.c
    @@ -416,7 +416,18 @@ static int bcm2835aux_spi_probe(struct platform_device *pdev)
    platform_set_drvdata(pdev, master);
    master->mode_bits = (SPI_CPOL | SPI_CS_HIGH | SPI_NO_CS);
    master->bits_per_word_mask = SPI_BPW_MASK(8);
    - master->num_chipselect = -1;
    + /* even though the driver never officially supported native CS
    + * allow a single native CS for legacy DT support purposes when
    + * no cs-gpio is configured.
    + * Known limitations for native cs are:
    + * * multiple chip-selects: cs0-cs2 are all simultaniously asserted
    + * whenever there is a transfer - this even includes SPI_NO_CS
    + * * SPI_CS_HIGH: is ignores - cs are always asserted low
    + * * cs_change: cs is deasserted after each spi_transfer
    + * * cs_delay_usec: cs is always deasserted one SCK cycle after
    + * a spi_transfer
    + */
    + master->num_chipselect = 1;
    master->transfer_one = bcm2835aux_spi_transfer_one;
    master->handle_err = bcm2835aux_spi_handle_err;
    master->prepare_message = bcm2835aux_spi_prepare_message;
    --
    2.20.1


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