[PATCH net-next] net: sfp: VSOL V2801F / CarlitoxxPro CPGOS03-0490 v2.0 workaround

[Russell King]

Add a workaround for the VSOL V2801F / CarlitoxxPro CPGOS03-0490 v2.0
GPON module which the manufacturer states needs single byte I2C reads
to the EEPROM.

Reported-by: Thomas Schreiber <tschre...@gmail.com>
Tested-by: Thomas Schreiber <tschre...@gmail.com>
Signed-off-by: Russell King <rmk+ker...@armlinux.org.uk>
---
 drivers/net/phy/sfp.c | 45 ++++++++++++++++++++++++++++++++++++++-----
 1 file changed, 40 insertions(+), 5 deletions(-)

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index debf91412a72..1e347afa951e 100644
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -219,6 +219,7 @@ struct sfp {
        struct sfp_bus *sfp_bus;
        struct phy_device *mod_phy;
        const struct sff_data *type;
+       size_t i2c_block_size;
        u32 max_power_mW;
 
        unsigned int (*get_state)(struct sfp *);
@@ -335,10 +336,19 @@ static int sfp_i2c_read(struct sfp *sfp, bool a2, u8 
dev_addr, void *buf,
                        size_t len)
 {
        struct i2c_msg msgs[2];
-       u8 bus_addr = a2 ? 0x51 : 0x50;
+       size_t block_size;
        size_t this_len;
+       u8 bus_addr;
        int ret;
 
+       if (a2) {
+               block_size = 16;
+               bus_addr = 0x51;
+       } else {
+               block_size = sfp->i2c_block_size;
+               bus_addr = 0x50;
+       }
+
        msgs[0].addr = bus_addr;
        msgs[0].flags = 0;
        msgs[0].len = 1;
@@ -350,8 +360,8 @@ static int sfp_i2c_read(struct sfp *sfp, bool a2, u8 
dev_addr, void *buf,
 
        while (len) {
                this_len = len;
-               if (this_len > 16)
-                       this_len = 16;
+               if (this_len > sfp->i2c_block_size)
+                       this_len = sfp->i2c_block_size;
 
                msgs[1].len = this_len;
 
@@ -1673,14 +1683,20 @@ static int sfp_sm_mod_probe(struct sfp *sfp, bool 
report)
        u8 check;
        int ret;
 
-       ret = sfp_read(sfp, false, 0, &id, sizeof(id));
+       /* Some modules (CarlitoxxPro CPGOS03-0490) do not support multibyte
+        * reads from the EEPROM, so start by reading the base identifying
+        * information one byte at a time.
+        */
+       sfp->i2c_block_size = 1;
+
+       ret = sfp_read(sfp, false, 0, &id.base, sizeof(id.base));
        if (ret < 0) {
                if (report)
                        dev_err(sfp->dev, "failed to read EEPROM: %d\n", ret);
                return -EAGAIN;
        }
 
-       if (ret != sizeof(id)) {
+       if (ret != sizeof(id.base)) {
                dev_err(sfp->dev, "EEPROM short read: %d\n", ret);
                return -EAGAIN;
        }
@@ -1719,6 +1735,25 @@ static int sfp_sm_mod_probe(struct sfp *sfp, bool report)
                }
        }
 
+       /* Some modules (Nokia 3FE46541AA) lock up if byte 0x51 is read as a
+        * single read. Switch back to reading 16 byte blocks unless we have
+        * a CarlitoxxPro module (rebranded VSOL V2801F).
+        */
+       if (memcmp(id.base.vendor_name, "VSOL            ", 16))
+               sfp->i2c_block_size = 16;
+
+       ret = sfp_read(sfp, false, SFP_CC_BASE + 1, &id.ext, sizeof(id.ext));
+       if (ret < 0) {
+               if (report)
+                       dev_err(sfp->dev, "failed to read EEPROM: %d\n", ret);
+               return -EAGAIN;
+       }
+
+       if (ret != sizeof(id.ext)) {
+               dev_err(sfp->dev, "EEPROM short read: %d\n", ret);
+               return -EAGAIN;
+       }
+
        check = sfp_check(&id.ext, sizeof(id.ext) - 1);
        if (check != id.ext.cc_ext) {
                if (cotsworks) {
-- 
2.20.1