Modifies the sun4i SPI master driver to make use of the
"spi-word-wait-ns" 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@xxxxxxxxx>
---
drivers/spi/spi-sun4i.c | 22 ++++++++++++++++++++++
1 file changed, 22 insertions(+)
diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c
index f60a6d6..3b4f5f4 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 +174,8 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
unsigned int tx_len = 0;
int ret = 0;
u32 reg;
+ 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 +264,25 @@ static int sun4i_spi_transfer_one(struct spi_master *master,
sun4i_spi_write(sspi, SUN4I_CLK_CTL_REG, reg);
+ /*
+ * Setup wait time between words.
+ *
+ * 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.
+ */
+ if (spi->word_wait_ns) {
+ clk_ns = DIV_ROUND_UP(1000000000, tfr->speed_hz);
+ wait_clk = DIV_ROUND_UP(spi->word_wait_ns, clk_ns) - 3;
+ if (wait_clk < 1) {
+ wait_clk = 1;
+ dev_dbg(&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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