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staging: fbtft: Do not hardcode SPI CS polarity inversion 

The current use of the mode flag SPI_CS_HIGH is fragile: it
overwrites anything already assigned by the SPI core.

Assign ^= SPI_CS_HIGH since we might be active high
already, and that is usually the case with GPIOs used
for chip select, even if they are in practice active low.

Add a comment clarifying why ^= SPI_CS_HIGH is the right
choice here.

Reported-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20191204233230.22309-1-linus.walleij@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
This commit is contained in:
Linus Walleij 2019-12-05 00:32:30 +01:00 committed by Greg Kroah-Hartman
parent 1184fd9966
commit 453a4b6d8e
2 changed files with 19 additions and 6 deletions
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12
drivers/staging/fbtft/fb_uc1611.c
View File

@ -63,11 +63,17 @@ static int init_display(struct fbtft_par *par)
{
int ret;
/* Set CS active high */
par->spi->mode |= SPI_CS_HIGH;
/*
* Set CS active inverse polarity: just setting SPI_CS_HIGH does not
* work with GPIO based chip selects that are logically active high
* but inverted inside the GPIO library, so enforce inverted
* semantics.
*/
par->spi->mode ^= SPI_CS_HIGH;
ret = spi_setup(par->spi);
if (ret) {
dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
dev_err(par->info->device,
"Could not set inverse CS polarity\n");
return ret;
}

13
drivers/staging/fbtft/fb_watterott.c
View File

@ -150,10 +150,17 @@ static int init_display(struct fbtft_par *par)
/* enable SPI interface by having CS and MOSI low during reset */
save_mode = par->spi->mode;
par->spi->mode |= SPI_CS_HIGH;
ret = spi_setup(par->spi); /* set CS inactive low */
/*
* Set CS active inverse polarity: just setting SPI_CS_HIGH does not
* work with GPIO based chip selects that are logically active high
* but inverted inside the GPIO library, so enforce inverted
* semantics.
*/
par->spi->mode ^= SPI_CS_HIGH;
ret = spi_setup(par->spi);
if (ret) {
dev_err(par->info->device, "Could not set SPI_CS_HIGH\n");
dev_err(par->info->device,
"Could not set inverse CS polarity\n");
return ret;
}
write_reg(par, 0x00); /* make sure mode is set */