[PATCH v2 1/1] spi: Assume GPIO CS active high in ACPI case

[Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>]

Currently GPIO CS handling, when descriptors are in use, doesn't
take into consideration that in ACPI case the default polarity
is Active High and can't be altered. Instead we have to use the
per-chip definition provided by SPISerialBus() resource.

Fixes: 766c6b63aa04 ("spi: fix client driver breakages when using GPIO descriptors")
Cc: Liguang Zhang <zhangliguang@xxxxxxxxxxxxxxxxx>
Cc: Jay Fang <f.fangjian@xxxxxxxxxx>
Cc: Sven Van Asbroeck <thesven73@xxxxxxxxx>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Tested-by: Xin Hao <xhao@xxxxxxxxxxxxxxxxx>
---
v2: refactor to avoid ternary (Mark, Sven), dropped comment changes (Mark)
 drivers/spi/spi.c | 22 ++++++++++++++++++----
 1 file changed, 18 insertions(+), 4 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index cd40421b8f55..36ee33514b40 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -820,15 +820,29 @@ static void spi_set_cs(struct spi_device *spi, bool enable, bool force)
 
 	if (spi->cs_gpiod || gpio_is_valid(spi->cs_gpio)) {
 		if (!(spi->mode & SPI_NO_CS)) {
-			if (spi->cs_gpiod)
-				/* polarity handled by gpiolib */
-				gpiod_set_value_cansleep(spi->cs_gpiod, activate);
-			else
+			if (spi->cs_gpiod) {
+				/*
+				 * Historically ACPI has no means of the GPIO polarity and
+				 * thus the SPISerialBus() resource defines it on the per-chip
+				 * basis. In order to avoid a chain of negations, the GPIO
+				 * polarity is considered being Active High. Even for the cases
+				 * when _DSD() is involved (in the updated versions of ACPI)
+				 * the GPIO CS polarity must be defined Active High to avoid
+				 * ambiguity. That's why we use enable, that takes SPI_CS_HIGH
+				 * into account.
+				 */
+				if (has_acpi_companion(&spi->dev))
+					gpiod_set_value_cansleep(spi->cs_gpiod, !enable);
+				else
+					/* Polarity handled by GPIO library */
+					gpiod_set_value_cansleep(spi->cs_gpiod, activate);
+			} else {
 				/*
 				 * invert the enable line, as active low is
 				 * default for SPI.
 				 */
 				gpio_set_value_cansleep(spi->cs_gpio, !enable);
+			}
 		}
 		/* Some SPI masters need both GPIO CS & slave_select */
 		if ((spi->controller->flags & SPI_MASTER_GPIO_SS) &&
-- 
2.30.2