Commit 453a4b6d authored by Linus Walleij's avatar Linus Walleij Committed by Greg Kroah-Hartman
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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: default avatarMark Brown <broonie@kernel.org>
Signed-off-by: default avatarLinus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20191204233230.22309-1-linus.walleij@linaro.org


Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 1184fd99

drivers/staging/fbtft/fb_uc1611.c

+9 −3
Original line number Diff line number Diff line
@@ -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;

	}

drivers/staging/fbtft/fb_watterott.c

+10 −3
Original line number Diff line number Diff line
@@ -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 */