Adds support and binding documentation for a new slave device property "sun4i,spi-word-wait-ns" that allows to set a hardware based delay between the transmission of words using the SPI Wait Clock Register. The SPI hardware needs 3 clock cycles to set up the delay, which makes the minimum non-zero wait time 4 clock cycles.
Signed-off-by: Marcus Weseloh <mweselo...@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 There is one review comment that I didn't address: Rob Herring suggested that this should be in the core-binding rather than in sun4i. I checked many of the hardware manuals of other SPI drivers and it looks to me like this hardware based inter-word delay is a feature that not many SPI controllers offer. And the SPI core currently has no way to control an inter-word delay, only inter-message. So I would like to propose this again as a sun4i binding, as it targets a sun4i (or sunxi?) specific hardware feature. --- .../devicetree/bindings/spi/spi-sun4i.txt | 11 +++++++++++ drivers/spi/spi-sun4i.c | 23 ++++++++++++++++++++++ 2 files changed, 34 insertions(+) diff --git a/Documentation/devicetree/bindings/spi/spi-sun4i.txt b/Documentation/devicetree/bindings/spi/spi-sun4i.txt index de827f5..d6c55fc 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-word-wait-ns: hardware based delay in nanoseconds between + transmission of words + 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>; + sun4i,spi-word-wait-ns = <12000>; + }; }; diff --git a/drivers/spi/spi-sun4i.c b/drivers/spi/spi-sun4i.c index f60a6d6..8cfd96c 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 beteen words */ + of_property_read_u32(spi->dev.of_node, "sun4i,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 -- You received this message because you are subscribed to the Google Groups "linux-sunxi" group. To unsubscribe from this group and stop receiving emails from it, send an email to linux-sunxi+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.