spi: Assume GPIO CS active high in ACPI case
PATCH 1/1 spi: Assume GPIO CS active high in ACPI case
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.
--- drivers/spi/spi.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-)
drivers/spi/spi.c +14 -3
@@ -820,12 +820,23 @@ 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 )) { +/* +* 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. +*/ +bool value =has_acpi_companion (&spi->dev) ? !enable : activate; +if (spi->cs_gpiod) -/* polarity handled by gpiolib */ -gpiod_set_value_cansleep (spi->cs_gpiod, activate); +/* Polarity handled by GPIO library */ +gpiod_set_value_cansleep (spi->cs_gpiod, value);else /* -* invert the enable line, as active low is +* Invert the enable line, as active low is * default for SPI. */ gpio_set_value_cansleep (spi->cs_gpio, !enable);
Signature · 1 line
2.30.2
Hi Andy, see below.
drivers/spi/spi.c static void spi_set_cs(struct spi_device *spi, bool enable, bool force) · line 832
Quoted 13 lines · Andy Shevchenko
if (spi->cs_gpiod || gpio_is_valid(spi->cs_gpio)) { if (!(spi->mode & SPI_NO_CS)) {drivers/spi/spi.c +10
-0+/* +* 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. +*/ +bool value =has_acpi_companion (&spi->dev) ? !enable : activate;
There are three booleans involved now: "value", "enable" and "activate". It might be quite hard for someone reading this code later, to work out what's going on? I've got to admit that my previous choice of "enable1" was also not perfect, to say the least...
AFAIK there are two basic concepts in this function:
- enable: indicates chip-select enabled or disabled (independent of gpio polarity)
- level : indicates the required level of the chip-select gpio
So maybe we can simplify like this?
static void spi_set_cs(struct spi_device *spi, bool enable, bool force) {
bool level = (spi->mode & SPI_CS_HIGH) ? enable : !enable;
if cs_gpio => use level : gpio_set_value_cansleep(level)
else if cs_gpiod(acpi) => use level : gpiod_set_value_cansleep(level)
else if cs_gpiod(_) => use enable :gpiod_set_value_cansleep(enable);
}
Mark Brown
maintainerdrivers/spi/spi.c static void spi_set_cs(struct spi_device *spi, bool enable, bool force) · line 832
Quoted 1 line · Andy Shevchenko
drivers/spi/spi.c +1
-0+bool value =has_acpi_companion (&spi->dev) ? !enable : activate;
Please write normal conditional statements to improve legibility.
drivers/spi/spi.c static void spi_set_cs(struct spi_device *spi, bool enable, bool force) · line 840
Quoted 10 lines
drivers/spi/spi.c +3
-3if (spi->cs_gpiod) -/* polarity handled by gpiolib */ -gpiod_set_value_cansleep (spi->cs_gpiod, activate); +/* Polarity handled by GPIO library */ +gpiod_set_value_cansleep (spi->cs_gpiod, value);else /* -* invert the enable line, as active low is +* Invert the enable line, as active low is * default for SPI.
The change would be clearer with the documentation formatting changes split out from the rest of it.
Quoted 5 lines · Mark Brown
drivers/spi/spi.c static void spi_set_cs(struct spi_device *spi, bool enable, bool force) · line 832
Quoted 1 line · Andy Shevchenko
drivers/spi/spi.c +1
-0+bool value =has_acpi_companion (&spi->dev) ? !enable : activate;Please write normal conditional statements to improve legibility.
OK!
Quoted 5 lines
Quoted 5 lines
drivers/spi/spi.c +2
-2if (spi->cs_gpiod) -/* polarity handled by gpiolib */ -gpiod_set_value_cansleep (spi->cs_gpiod, activate); +/* Polarity handled by GPIO library */ +gpiod_set_value_cansleep (spi->cs_gpiod, value);
Quoted 8 lines
drivers/spi/spi.c static void spi_set_cs(struct spi_device *spi, bool enable, bool force) · line 840
Quoted 5 lines
drivers/spi/spi.c +1
-1else /* -* invert the enable line, as active low is +* Invert the enable line, as active low is * default for SPI. The change would be clearer with the documentation formatting changes split out from the rest of it.
Will remove these changes from a fix in v2.
P.S> something is odd about the series I have submitted, i.e. half of the patches simply didn't make it. I would wait with any new submission until it will be clarified, otherwise it's a chance to miss more patches without any reason why.
Signature · 2 lines
With Best Regards, Andy Shevchenko