Adds support and documentation for a new slave device property
"sun4i,spi-wdelay" that allows to set the SPI Wait Clock Register per
device / transfer. The SPI hardware will wait the specified amount of
SPI clock periods (plus a constant 3 clock periods) before transmitting
the next word.
The constant additional 3 clock periods are not documented by the vendor
and have been determined by analyzing the generated waveforms across
many different transmission speeds.
Signed-off-by: Marcus Weseloh <mweselo...@gmail.com>
---
Documentation/devicetree/bindings/spi/spi-sun4i.txt | 11 +++++++++++
drivers/spi/spi-sun4i.c | 7 +++++++
2 files changed, 18 insertions(+)
diff --git a/Documentation/devicetree/bindings/spi/spi-sun4i.txt
b/Documentation/devicetree/bindings/spi/spi-sun4i.txt
index de827f5..9c4d723 100644
--- a/Documentation/devicetree/bindings/spi/spi-sun4i.txt
+++ b/Documentation/devicetree/bindings/spi/spi-sun4i.txt
@@ -10,6 +10,10 @@ Required properties:
- "mod": the parent module clock
- clock-names: Must contain the clock names described just above
+Optional properties for slave devices:
+- sun4i,spi-wdelay : delay between transmission of words, specified in number
+ of SPI clock periods (actual delay is wdelay + 3 clock periods)
+
Example:
spi1: spi@01c06000 {
@@ -21,4 +25,11 @@ spi1: spi@01c06000 {
status = "disabled";
#address-cells = <1>;
#size-cells = <0>;
+
+ spi1_0 {
+ compatible = "example,dummy";
+ reg = <0>;
+ spi-max-frequency = <1000000>; /* 1Mhz = 1us clock period */
+ sun4i,spi-wdelay = <2>; /* delay 5us (2 + 3 clock periods) */
+ };
};
diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index f60a6d6..a8e39f1 100644
--- a/drivers/spi/spi-sun4i.c
+++ b/drivers/spi/spi-sun4i.c
@@ -19,6 +19,7 @@
#include <linux/module.h>
#include <linux/platform_device.h>
#include <linux/pm_runtime.h>
+#include <linux/of.h>
#include <linux/spi/spi.h>
@@ -173,6 +174,7 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
unsigned int tx_len = 0;
int ret = 0;
u32 reg;
+ u32 wdelay = 0;
/* We don't support transfer larger than the FIFO */
if (tfr->len > SUN4I_FIFO_DEPTH)
@@ -261,6 +263,11 @@ static int sun4i_spi_transfer_one(struct spi_master
*master,
sun4i_spi_write(sspi, SUN4I_CLK_CTL_REG, reg);
+ /* Set optional inter-word wait cycles */
+ of_property_read_u32(spi->dev.of_node, "sun4i,spi-wdelay",
+ &wdelay);
+ sun4i_spi_write(sspi, SUN4I_WAIT_REG, (u16)wdelay);
+
/* Setup the transfer now... */
if (sspi->tx_buf)
tx_len = tfr->len;
--
1.9.1
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