[PATCH v1 3/3] drivers: xilinx_spi: Probe fifo_depth at runtime

[Mayuresh Chitale]

If the fifo-size DT parameter is not provided then probe the
controller's fifo depth at runtime. This is ported from a patch
in the Linux Xilinx SPI driver.

Signed-off-by: Mayuresh Chitale <mchit...@ventanamicro.com>
Link: 
https://lore.kernel.org/r/1422029330-10971-5-git-send-email-ricardo.riba...@gmail.com
---
 drivers/spi/xilinx_spi.c | 23 +++++++++++++++++++++++
 1 file changed, 23 insertions(+)

diff --git a/drivers/spi/xilinx_spi.c b/drivers/spi/xilinx_spi.c
index b63cda2091..99ae5be291 100644
--- a/drivers/spi/xilinx_spi.c
+++ b/drivers/spi/xilinx_spi.c
@@ -109,6 +109,27 @@ struct xilinx_spi_priv {
        u8 startup;
 };
 
+static int xilinx_spi_find_buffer_size(struct xilinx_spi_regs *regs)
+{
+       u8 sr;
+       int n_words = 0;
+
+       /*
+        * Before the buffer_size detection we reset the core
+        * to make sure we start with a clean state.
+        */
+       writel(SPISSR_RESET_VALUE, &regs->srr);
+
+       /* Fill the Tx FIFO with as many words as possible */
+       do {
+               writel(0, &regs->spidtr);
+               sr = readl(&regs->spisr);
+               n_words++;
+       } while (!(sr & SPISR_TX_FULL));
+
+       return n_words;
+}
+
 static int xilinx_spi_probe(struct udevice *bus)
 {
        struct xilinx_spi_priv *priv = dev_get_priv(bus);
@@ -116,6 +137,8 @@ static int xilinx_spi_probe(struct udevice *bus)
 
        regs = priv->regs = dev_read_addr_ptr(bus);
        priv->fifo_depth = dev_read_u32_default(bus, "fifo-size", 0);
+       if (!priv->fifo_depth)
+               priv->fifo_depth = xilinx_spi_find_buffer_size(regs);
 
        writel(SPISSR_RESET_VALUE, &regs->srr);
 
-- 
2.34.1