net: dsa/mv88e6xxx: add reg read and write debug

This commit adds debug messages for the generic mv88e6xxx read and write
routines. The output is similar to this:

    mdio-gpio mdio-gpio.0: <- addr: 0x1b reg: 0x05 val: 0x4000
    mdio-gpio mdio-gpio.0: -> addr: 0x1b reg: 0x07 val: 0x3113
    mdio-gpio mdio-gpio.0: -> addr: 0x1b reg: 0x08 val: 0x0330
    mdio-gpio mdio-gpio.0: -> addr: 0x1b reg: 0x09 val: 0x0000

This is convenient to dynamically debug operations through debugfs with:

    echo file mv88e6xxx.c +p > <debugfs>/dynamic_debug/control

Signed-off-by: Vivien Didelot <vivien.didelot@savoirfairelinux.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 9 insertions, 0 deletions

diff --git a/drivers/net/dsa/mv88e6xxx.c b/drivers/net/dsa/mv88e6xxx.c
index cd6807c6b4ed..3e7e31a6abb7 100644
--- a/drivers/net/dsa/mv88e6xxx.c
+++ b/drivers/net/dsa/mv88e6xxx.c
@@ -85,6 +85,12 @@ int mv88e6xxx_reg_read(struct dsa_switch *ds, int addr, int reg)
         ret = __mv88e6xxx_reg_read(bus, ds->pd->sw_addr, addr, reg);
         mutex_unlock(&ps->smi_mutex);
 
+        if (ret < 0)
+                return ret;
+
+        dev_dbg(ds->master_dev, "<- addr: 0x%.2x reg: 0x%.2x val: 0x%.4x\n",
+                addr, reg, ret);
+
         return ret;
 }
 
@@ -128,6 +134,9 @@ int mv88e6xxx_reg_write(struct dsa_switch *ds, int addr, int reg, u16 val)
         if (bus == NULL)
                 return -EINVAL;
 
+        dev_dbg(ds->master_dev, "-> addr: 0x%.2x reg: 0x%.2x val: 0x%.4x\n",
+                addr, reg, val);
+
         mutex_lock(&ps->smi_mutex);
         ret = __mv88e6xxx_reg_write(bus, ds->pd->sw_addr, addr, reg, val);
         mutex_unlock(&ps->smi_mutex);