fsi: aspeed: Run the bus at maximum speed

Testing of Tacoma has shown that the ASPEED master can be run at maximum
speed.

The exception is when wired externally with a cable, in which case we
use a divisor of two to ensure reliable operation.

Reviewed-by: Eddie James <eajames@linux.ibm.com>
Link: https://lore.kernel.org/r/20200728025527.174503-4-joel@jms.id.au
Signed-off-by: Joel Stanley <joel@jms.id.au>

diff --git a/drivers/fsi/fsi-master-aspeed.c b/drivers/fsi/fsi-master-aspeed.c
index c282de76e6e7355eefec638011e4d11616cc92cb..f503f64ab32bfdc3cffc0a2407a6127d9dcbf360 100644 (file)
--- a/drivers/fsi/fsi-master-aspeed.c
+++ b/drivers/fsi/fsi-master-aspeed.c
@@ -83,7 +83,11 @@ static const u32 fsi_base = 0xa0000000;
 
 #define FSI_LINK_ENABLE_SETUP_TIME     10      /* in mS */
 
-#define DEFAULT_DIVISOR                        14
+/* Run the bus at maximum speed by default */
+#define FSI_DIVISOR_DEFAULT            1
+#define FSI_DIVISOR_CABLED             2
+static u16 aspeed_fsi_divisor = FSI_DIVISOR_DEFAULT;
+
 #define OPB_POLL_TIMEOUT               10000
 
 static int __opb_write(struct fsi_master_aspeed *aspeed, u32 addr,
@@ -385,9 +389,11 @@ static int aspeed_master_init(struct fsi_master_aspeed *aspeed)
        opb_writel(aspeed, ctrl_base + FSI_MECTRL, reg);
 
        reg = cpu_to_be32(FSI_MMODE_ECRC | FSI_MMODE_EPC | FSI_MMODE_RELA
-                       | fsi_mmode_crs0(DEFAULT_DIVISOR)
-                       | fsi_mmode_crs1(DEFAULT_DIVISOR)
+                       | fsi_mmode_crs0(aspeed_fsi_divisor)
+                       | fsi_mmode_crs1(aspeed_fsi_divisor)
                        | FSI_MMODE_P8_TO_LSB);
+       dev_info(aspeed->dev, "mmode set to %08x (divisor %d)\n",
+                       be32_to_cpu(reg), aspeed_fsi_divisor);
        opb_writel(aspeed, ctrl_base + FSI_MMODE, reg);
 
        reg = cpu_to_be32(0xffff0000);
@@ -446,6 +452,11 @@ static int tacoma_cabled_fsi_fixup(struct device *dev)
 
        /* If the routing GPIO is high we should set the mux to low. */
        if (gpio) {
+               /*
+                * Cable signal integrity means we should run the bus
+                * slightly slower
+                */
+               aspeed_fsi_divisor = FSI_DIVISOR_CABLED;
                gpiod_direction_output(mux_gpio, 0);
                dev_info(dev, "FSI configured for external cable\n");
        } else {