lkml.org 
[lkml]   [2020]   [Feb]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
Patch in this message
/
From
Subject[PATCH 4.4 19/91] mmc: spi: Toggle SPI polarity, do not hardcode it
Date
From: Linus Walleij <linus.walleij@linaro.org>

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>

---
drivers/mmc/host/mmc_spi.c | 11 ++++++++---
1 file changed, 8 insertions(+), 3 deletions(-)

--- a/drivers/mmc/host/mmc_spi.c
+++ b/drivers/mmc/host/mmc_spi.c
@@ -1153,17 +1153,22 @@ static void mmc_spi_initsequence(struct
* 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,

\
 
 \ /
  Last update: 2020-02-13 17:11    [W:0.268 / U:33.800 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site