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authorMartin Sperl <kernel@martin.sperl.org>2019-02-23 08:49:48 +0000
committerMark Brown <broonie@kernel.org>2019-05-08 18:28:51 +0900
commit0ff2de8bb163551ec4230a5a6f3c40c1f6adec4f (patch)
treee144d1f35586e40c4048cf982a63eeff126186ba /drivers/spi
parent154f7da56f1ecba42021d550c9e8432ac8d32c26 (diff)
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spi: core: allow defining time that cs is deasserted
For some SPI devices that support speed_hz > 1MHz the default 10 us delay when cs_change = 1 is typically way to long and may result in poor spi bus utilization. This patch makes it possible to control the delay at micro or nano second resolution on a per spi_transfer basis. It even allows an "as fast as possible" mode with: xfer.cs_change_delay_unit = SPI_DELAY_UNIT_NSECS; xfer.cs_change_delay = 0; The delay code is shared between delay_usecs and cs_change_delay for consistency and reuse, so in the future this change_delay_unit could also apply to delay_usec as well. Note that on slower SOCs/CPU actually reaching ns deasserts on cs is not realistic as the gpio overhead alone (without any delays added ) may already leave cs deasserted for more than 1us - at least on a raspberry pi. But at the very least this way we can keep it as short as possible. Signed-off-by: Martin Sperl <kernel@martin.sperl.org> Signed-off-by: Mark Brown <broonie@kernel.org>
Diffstat (limited to 'drivers/spi')
-rw-r--r--drivers/spi/spi.c59
1 files changed, 49 insertions, 10 deletions
diff --git a/drivers/spi/spi.c b/drivers/spi/spi.c
index 5e75944ad5d1..7e8ffe3fdc00 100644
--- a/drivers/spi/spi.c
+++ b/drivers/spi/spi.c
@@ -1090,6 +1090,52 @@ static int spi_transfer_wait(struct spi_controller *ctlr,
return 0;
}
+static void _spi_transfer_delay_ns(u32 ns)
+{
+ if (!ns)
+ return;
+ if (ns <= 1000) {
+ ndelay(ns);
+ } else {
+ u32 us = DIV_ROUND_UP(ns, 1000);
+
+ if (us <= 10)
+ udelay(us);
+ else
+ usleep_range(us, us + DIV_ROUND_UP(us, 10));
+ }
+}
+
+static void _spi_transfer_cs_change_delay(struct spi_message *msg,
+ struct spi_transfer *xfer)
+{
+ u32 delay = xfer->cs_change_delay;
+ u32 unit = xfer->cs_change_delay_unit;
+
+ /* return early on "fast" mode - for everything but USECS */
+ if (!delay && unit != SPI_DELAY_UNIT_USECS)
+ return;
+
+ switch (unit) {
+ case SPI_DELAY_UNIT_USECS:
+ /* for compatibility use default of 10us */
+ if (!delay)
+ delay = 10000;
+ else
+ delay *= 1000;
+ break;
+ case SPI_DELAY_UNIT_NSECS: /* nothing to do here */
+ break;
+ default:
+ dev_err_once(&msg->spi->dev,
+ "Use of unsupported delay unit %i, using default of 10us\n",
+ xfer->cs_change_delay_unit);
+ delay = 10000;
+ }
+ /* now sleep for the requested amount of time */
+ _spi_transfer_delay_ns(delay);
+}
+
/*
* spi_transfer_one_message - Default implementation of transfer_one_message()
*
@@ -1148,14 +1194,8 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
if (msg->status != -EINPROGRESS)
goto out;
- if (xfer->delay_usecs) {
- u16 us = xfer->delay_usecs;
-
- if (us <= 10)
- udelay(us);
- else
- usleep_range(us, us + DIV_ROUND_UP(us, 10));
- }
+ if (xfer->delay_usecs)
+ _spi_transfer_delay_ns(xfer->delay_usecs * 1000);
if (xfer->cs_change) {
if (list_is_last(&xfer->transfer_list,
@@ -1163,7 +1203,7 @@ static int spi_transfer_one_message(struct spi_controller *ctlr,
keep_cs = true;
} else {
spi_set_cs(msg->spi, false);
- udelay(10);
+ _spi_transfer_cs_change_delay(msg, xfer);
spi_set_cs(msg->spi, true);
}
}
@@ -3757,4 +3797,3 @@ err0:
* include needing to have boardinfo data structures be much more public.
*/
postcore_initcall(spi_init);
-