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Subject[PATCH v3] spi: dts: sun4i: Add support for hardware-based wait time between words
Date
Adds a new property "spi-word-wait-ns" to the spi-bus binding that allows
SPI slave devices to set a hardware based wait time between the
transmission of words. Also modifies the sun4i SPI master driver to make
use of the new property. This specific SPI controller needs 3 clock
cycles to set up the delay, which makes the minimum non-zero wait time
on this hardware 4 clock cycles.

Signed-off-by: Marcus Weseloh <mweseloh42@gmail.com>
---
Changes from v1:
* renamed the property for more clarity
* wait time is set in nanoseconds instead of number of clock cycles
* transparently handle the 3 setup clock cycles

Changes from v2:
* fixed typo in comment
* moved parameter to spi-bus binding, dropping the vendor prefix
* changed commit summary and description to reflect the changes
---
Documentation/devicetree/bindings/spi/spi-bus.txt | 2 ++
drivers/spi/spi-sun4i.c | 23 +++++++++++++++++++++++
2 files changed, 25 insertions(+)

diff --git a/Documentation/devicetree/bindings/spi/spi-bus.txt b/Documentation/devicetree/bindings/spi/spi-bus.txt
index bbaa857..2d6034f 100644
--- a/Documentation/devicetree/bindings/spi/spi-bus.txt
+++ b/Documentation/devicetree/bindings/spi/spi-bus.txt
@@ -61,6 +61,8 @@ contain the following properties.
used for MOSI. Defaults to 1 if not present.
- spi-rx-bus-width - (optional) The bus width(number of data wires) that
used for MISO. Defaults to 1 if not present.
+- spi-word-wait-ns - (optional) Hardware based delay between transmission of
+ words in nanoseconds

Some SPI controllers and devices support Dual and Quad SPI transfer mode.
It allows data in the SPI system to be transferred in 2 wires(DUAL) or 4 wires(QUAD).
diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index f60a6d6..73995a1 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 +174,9 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
unsigned int tx_len = 0;
int ret = 0;
u32 reg;
+ u32 wait_ns = 0;
+ int wait_clk = 0;
+ int clk_ns = 0;

/* We don't support transfer larger than the FIFO */
if (tfr->len > SUN4I_FIFO_DEPTH)
@@ -261,6 +265,25 @@ static int sun4i_spi_transfer_one(struct spi_master *master,

sun4i_spi_write(sspi, SUN4I_CLK_CTL_REG, reg);

+ /* Setup wait time between words */
+ of_property_read_u32(spi->dev.of_node, "spi-word-wait-ns",
+ &wait_ns);
+ if (wait_ns) {
+ /* The wait time is set in SPI_CLK cycles. The SPI hardware
+ * needs 3 additional cycles to setup the wait counter, so
+ * the minimum delay time is 4 cycles.
+ */
+ clk_ns = DIV_ROUND_UP(1000000000, tfr->speed_hz);
+ wait_clk = DIV_ROUND_UP(wait_ns, clk_ns) - 3;
+ if (wait_clk < 1) {
+ wait_clk = 1;
+ dev_info(&spi->dev,
+ "using minimum of 4 word wait cycles (%uns)",
+ 4 * clk_ns);
+ }
+ }
+ sun4i_spi_write(sspi, SUN4I_WAIT_REG, (u16)wait_clk);
+
/* Setup the transfer now... */
if (sspi->tx_buf)
tx_len = tfr->len;
--
1.9.1


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