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Subject[PATCH v4 02/19] spi: introduce spi_delay struct as "value + unit" & spi_delay_exec()
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There are plenty of delays that have been introduced in SPI core. Most of
them are in micro-seconds, some need to be in nano-seconds, and some in
clock-cycles.

For some of these delays (related to transfers & CS timing) it may make
sense to have a `spi_delay` struct that abstracts these a bit.

The important element of these delays [for unification] seems to be the
`unit` of the delay.
It looks like micro-seconds is good enough for most people, but every-once
in a while, some delays seem to require other units of measurement.

This change adds the `spi_delay` struct & a `spi_delay_exec()` function
that processes a `spi_delay` object/struct to execute the delay.
It's a copy of the `cs_change_delay` mechanism, but without the default
for 10 uS.

The clock-cycle delay unit is a bit special, as it needs to be bound to an
`spi_transfer` object to execute.

Signed-off-by: Alexandru Ardelean <alexandru.ardelean@analog.com>
---
drivers/spi/spi.c | 51 +++++++++++++++++++++++++++++++++++++++++
include/linux/spi/spi.h | 18 ++++++++++++---
2 files changed, 66 insertions(+), 3 deletions(-)

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index c90e02e6d62f..1883de8ffa82 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1106,6 +1106,57 @@ static void _spi_transfer_delay_ns(u32 ns)
}
}

+static int _spi_delay_to_ns(struct spi_delay *_delay, struct spi_transfer *xfer)
+{
+ u32 delay = _delay->value;
+ u32 unit = _delay->unit;
+ u32 hz;
+
+ if (!delay)
+ return 0;
+
+ switch (unit) {
+ case SPI_DELAY_UNIT_USECS:
+ delay *= 1000;
+ break;
+ case SPI_DELAY_UNIT_NSECS: /* nothing to do here */
+ break;
+ case SPI_DELAY_UNIT_SCK:
+ /* clock cycles need to be obtained from spi_transfer */
+ if (!xfer)
+ return -EINVAL;
+ /* if there is no effective speed know, then approximate
+ * by underestimating with half the requested hz
+ */
+ hz = xfer->effective_speed_hz ?: xfer->speed_hz / 2;
+ if (!hz)
+ return -EINVAL;
+ delay *= DIV_ROUND_UP(1000000000, hz);
+ break;
+ default:
+ return -EINVAL;
+ }
+
+ return delay;
+}
+
+int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer)
+{
+ int delay;
+
+ if (!_delay)
+ return -EINVAL;
+
+ delay = _spi_delay_to_ns(_delay, xfer);
+ if (delay < 0)
+ return delay;
+
+ _spi_transfer_delay_ns(delay);
+
+ return 0;
+}
+EXPORT_SYMBOL_GPL(spi_delay_exec);
+
static void _spi_transfer_cs_change_delay(struct spi_message *msg,
struct spi_transfer *xfer)
{
diff --git a/include/linux/spi/spi.h b/include/linux/spi/spi.h
index af4f265d0f67..c18cfa7cda35 100644
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -89,6 +89,21 @@ void spi_statistics_add_transfer_stats(struct spi_statistics *stats,
#define SPI_STATISTICS_INCREMENT_FIELD(stats, field) \
SPI_STATISTICS_ADD_TO_FIELD(stats, field, 1)

+/**
+ * struct spi_delay - SPI delay information
+ * @value: Value for the delay
+ * @unit: Unit for the delay
+ */
+struct spi_delay {
+#define SPI_DELAY_UNIT_USECS 0
+#define SPI_DELAY_UNIT_NSECS 1
+#define SPI_DELAY_UNIT_SCK 2
+ u16 value;
+ u8 unit;
+};
+
+extern int spi_delay_exec(struct spi_delay *_delay, struct spi_transfer *xfer);
+
/**
* struct spi_device - Controller side proxy for an SPI slave device
* @dev: Driver model representation of the device.
@@ -834,9 +849,6 @@ struct spi_transfer {
u16 delay_usecs;
u16 cs_change_delay;
u8 cs_change_delay_unit;
-#define SPI_DELAY_UNIT_USECS 0
-#define SPI_DELAY_UNIT_NSECS 1
-#define SPI_DELAY_UNIT_SCK 2
u32 speed_hz;
u16 word_delay;

--
2.20.1
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