[RFC PATCH] net: dsa: mv88e6xxx: support single chip sw_addr offset

[Rasmus Villemoes]

From: Per Noergaard Christensen <p...@deif.com>

The 88e6250 does not support multi-chip addressing. However, one can
still have two of them on the same mdio bus, since the device only
uses 16 of the 32 possible addresses, either addresses 0x00-0x0F or
0x10-0x1F depending on the ADDR4 pin at reset [since ADDR4 is
internally pulled high, the latter is the default].

In order to prepare for supporting the 88e6250, change
mv88e6xxx_smi_init and the single_chip_{read,write} functions to allow
and honour a non-zero sw_addr in single chip mode. Since this only
changes the behaviour in the sw_addr!=0 && !chip->info->multi_chip
case from returning -EINVAL, it should not break existing setups.

Signed-off-by: Per Noergaard Christensen <p...@deif.com>
[RV: reword commit message]
Signed-off-by: Rasmus Villemoes <rasmus.villem...@prevas.dk>
---
 drivers/net/dsa/mv88e6xxx/chip.c | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/drivers/net/dsa/mv88e6xxx/chip.c b/drivers/net/dsa/mv88e6xxx/chip.c
index 9588a5f8719b..b482058d11dc 100644
--- a/drivers/net/dsa/mv88e6xxx/chip.c
+++ b/drivers/net/dsa/mv88e6xxx/chip.c
@@ -87,7 +87,7 @@ static int mv88e6xxx_smi_single_chip_read(struct 
mv88e6xxx_chip *chip,
 {
        int ret;
 
-       ret = mdiobus_read_nested(chip->bus, addr, reg);
+       ret = mdiobus_read_nested(chip->bus, addr + chip->sw_addr, reg);
        if (ret < 0)
                return ret;
 
@@ -101,7 +101,7 @@ static int mv88e6xxx_smi_single_chip_write(struct 
mv88e6xxx_chip *chip,
 {
        int ret;
 
-       ret = mdiobus_write_nested(chip->bus, addr, reg, val);
+       ret = mdiobus_write_nested(chip->bus, addr + chip->sw_addr, reg, val);
        if (ret < 0)
                return ret;
 
@@ -4601,11 +4601,12 @@ static struct mv88e6xxx_chip 
*mv88e6xxx_alloc_chip(struct device *dev)
 static int mv88e6xxx_smi_init(struct mv88e6xxx_chip *chip,
                              struct mii_bus *bus, int sw_addr)
 {
-       if (sw_addr == 0)
-               chip->smi_ops = &mv88e6xxx_smi_single_chip_ops;
-       else if (chip->info->multi_chip)
-               chip->smi_ops = &mv88e6xxx_smi_multi_chip_ops;
-       else
+       if (sw_addr >= 0 && sw_addr <= 31) {
+               if (chip->info->multi_chip && sw_addr)
+                       chip->smi_ops = &mv88e6xxx_smi_multi_chip_ops;
+               else
+                       chip->smi_ops = &mv88e6xxx_smi_single_chip_ops;
+       } else
                return -EINVAL;
 
        chip->bus = bus;
-- 
2.20.1