spi/dw_spi: add a FIFO depth detection

FIFO depth is configurable for each implementation of DW core,
so add a depth detection for those interface drivers who don't set
the fifo_len explicitly

Signed-off-by: Feng Tang <feng.tang@intel.com>
Acked-by: Jean-Hugues Deschenes <jean-hugues.deschenes@octasic.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

1 files changed, 16 insertions, 0 deletions

diff --git a/drivers/spi/dw_spi.c b/drivers/spi/dw_spi.c
index f713af8309e3..d948ef4f3910 100644
--- a/drivers/spi/dw_spi.c
+++ b/drivers/spi/dw_spi.c
@@ -831,6 +831,22 @@ static void spi_hw_init(struct dw_spi *dws)
         spi_mask_intr(dws, 0xff);
         spi_enable_chip(dws, 1);
         flush(dws);
+
+        /*
+         * Try to detect the FIFO depth if not set by interface driver,
+         * the depth could be from 2 to 256 from HW spec
+         */
+        if (!dws->fifo_len) {
+                u32 fifo;
+                for (fifo = 2; fifo <= 257; fifo++) {
+                        dw_writew(dws, txfltr, fifo);
+                        if (fifo != dw_readw(dws, txfltr))
+                                break;
+                }
+
+                dws->fifo_len = (fifo == 257) ? 0 : fifo;
+                dw_writew(dws, txfltr, 0);
+        }
 }
 
 int __devinit dw_spi_add_host(struct dw_spi *dws)