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Subject[PATCH v4 15/19] spi: implement SW control for CS times
Date
This change implements CS control for setup, hold & inactive delays.

The `cs_setup` delay is completely new, and can help with cases where
asserting the CS, also brings the device out of power-sleep, where there
needs to be a longer (than usual), before transferring data.

The `cs_hold` time can overlap with the `delay` (or `delay_usecs`) from an
SPI transfer. The main difference is that `cs_hold` implies that CS will be
de-asserted.

The `cs_inactive` delay does not have a clear use-case yet. It has been
implemented mostly because the `spi_set_cs_timing()` function implements
it. To some degree, this could overlap or replace `cs_change_delay`, but
this will require more consideration/investigation in the future.

All these delays have been added to the `spi_controller` struct, as they
would typically be configured by calling `spi_set_cs_timing()` after an
`spi_setup()` call.

Software-mode for CS control, implies that the `set_cs_timing()` hook has
not been provided for the `spi_controller` object.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
drivers/spi/spi.c | 45 ++++++++++++++++++++++++++++++++++++++++-
include/linux/spi/spi.h | 5 +++++
2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 122af2264bfe..61ef286f954a 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -775,6 +775,15 @@ int spi_register_board_info(struct spi_board_info const *info, unsigned n)

static void spi_set_cs(struct spi_device *spi, bool enable)
{
+ bool enable1 = enable;
+
+ if (!spi->controller->set_cs_timing) {
+ if (enable1)
+ spi_delay_exec(&spi->controller->cs_setup, NULL);
+ else
+ spi_delay_exec(&spi->controller->cs_hold, NULL);
+ }
+
if (spi->mode & SPI_CS_HIGH)
enable = !enable;

@@ -800,6 +809,11 @@ static void spi_set_cs(struct spi_device *spi, bool enable)
} else if (spi->controller->set_cs) {
spi->controller->set_cs(spi, !enable);
}
+
+ if (!spi->controller->set_cs_timing) {
+ if (!enable1)
+ spi_delay_exec(&spi->controller->cs_inactive, NULL);
+ }
}

#ifdef CONFIG_HAS_DMA
@@ -3156,10 +3170,39 @@ EXPORT_SYMBOL_GPL(spi_setup);
int spi_set_cs_timing(struct spi_device *spi, struct spi_delay *setup,
struct spi_delay *hold, struct spi_delay *inactive)
{
+ size_t len;
+
if (spi->controller->set_cs_timing)
return spi->controller->set_cs_timing(spi, setup, hold,
inactive);
- return -ENOTSUPP;
+
+ if ((setup && setup->unit == SPI_DELAY_UNIT_SCK) ||
+ (hold && hold->unit == SPI_DELAY_UNIT_SCK) ||
+ (inactive && inactive->unit == SPI_DELAY_UNIT_SCK)) {
+ dev_err(&spi->dev,
+ "Clock-cycle delays for CS not supported in SW mode\n");
+ return -ENOTSUPP;
+ }
+
+ len = sizeof(struct spi_delay);
+
+ /* copy delays to controller */
+ if (setup)
+ memcpy(&spi->controller->cs_setup, setup, len);
+ else
+ memset(&spi->controller->cs_setup, 0, len);
+
+ if (hold)
+ memcpy(&spi->controller->cs_hold, hold, len);
+ else
+ memset(&spi->controller->cs_hold, 0, len);
+
+ if (inactive)
+ memcpy(&spi->controller->cs_inactive, inactive, len);
+ else
+ memset(&spi->controller->cs_inactive, 0, len);
+
+ return 0;
}
EXPORT_SYMBOL_GPL(spi_set_cs_timing);

diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index 592e50aae998..66031c8d0093 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -602,6 +602,11 @@ struct spi_controller {
/* Optimized handlers for SPI memory-like operations. */
const struct spi_controller_mem_ops *mem_ops;

+ /* CS delays */
+ struct spi_delay cs_setup;
+ struct spi_delay cs_hold;
+ struct spi_delay cs_inactive;
+
/* gpio chip select */
int *cs_gpios;
struct gpio_desc **cs_gpiods;
--
2.20.1
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