mmc: spi: Toggle SPI polarity, do not hardcode it

commit af3ed119329cf9690598c5a562d95dfd128e91d6 upstream.

The code in mmc_spi_initsequence() tries to send a burst with
high chipselect and for this reason hardcodes the device into
SPI_CS_HIGH.

This is not good because the SPI_CS_HIGH flag indicates
logical "asserted" CS not always the physical level. In
some cases the signal is inverted in the GPIO library and
in that case SPI_CS_HIGH is already set, and enforcing
SPI_CS_HIGH again will actually drive it low.

Instead of hard-coding this, toggle the polarity so if the
default is LOW it goes high to assert chipselect but if it
is already high then toggle it low instead.

Cc: Phil Elwell <phil@raspberrypi.org>
Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Mark Brown <broonie@kernel.org>
Link: https://lore.kernel.org/r/20191204152749.12652-1-linus.walleij@linaro.org
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/mmc/host/mmc_spi.c b/drivers/mmc/host/mmc_spi.c
index c2df68e..279d5da 100644 (file)
--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1157,17 +1157,22 @@ static void mmc_spi_initsequence(struct mmc_spi_host *host)
         * SPI protocol.  Another is that when chipselect is released while
         * the card returns BUSY status, the clock must issue several cycles
         * with chipselect high before the card will stop driving its output.
+        *
+        * SPI_CS_HIGH means "asserted" here. In some cases like when using
+        * GPIOs for chip select, SPI_CS_HIGH is set but this will be logically
+        * inverted by gpiolib, so if we want to ascertain to drive it high
+        * we should toggle the default with an XOR as we do here.
         */
-       host->spi->mode |= SPI_CS_HIGH;
+       host->spi->mode ^= SPI_CS_HIGH;
        if (spi_setup(host->spi) != 0) {
                /* Just warn; most cards work without it. */
                dev_warn(&host->spi->dev,
                                "can't change chip-select polarity\n");
-               host->spi->mode &= ~SPI_CS_HIGH;
+               host->spi->mode ^= SPI_CS_HIGH;
        } else {
                mmc_spi_readbytes(host, 18);
 
-               host->spi->mode &= ~SPI_CS_HIGH;
+               host->spi->mode ^= SPI_CS_HIGH;
                if (spi_setup(host->spi) != 0) {
                        /* Wot, we can't get the same setup we had before? */
                        dev_err(&host->spi->dev,