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SubjectRe: [PATCH v3] spi: dts: sun4i: Add support for hardware-based wait time between words
On Mon, Dec 14, 2015 at 12:04:11AM +0100, Marcus Weseloh wrote:
> 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

Could be a software delay if the h/w doesn't support delays.

> 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);

Read this in probe and save the value rather than fetching every
transfer.

> + 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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