spi: introduce spi_delay struct as "value + unit" & spi_delay_exec()

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>
Link: https://lore.kernel.org/r/20190926105147.7839-3-alexandru.ardelean@analog.com
Signed-off-by: Mark Brown <broonie@kernel.org>

diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 7ba981cdb86bde1e752f6ecc8ba020b2d368ecb1..7499a4efbaba5b24a5c62446485a2e8d56395ea9 100644 (file)
--- 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 27f6b046cf92312d632af0307a34df9a2b2f4428..8f643de3197b4d78c51e42ae69606ccc4f6fab27 100644 (file)
--- a/include/linux/spi/spi.h
+++ b/include/linux/spi/spi.h
@@ -90,6 +90,21 @@ 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.
@@ -887,9 +902,6 @@ 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;