net: sfp: read eeprom in maximum 16 byte increments

[ Upstream commit 28e74a7cfd6403f0d1c0f8b10b45d6fae37b227e ]

Some SFP modules do not like reads longer than 16 bytes, so read the
EEPROM in chunks of 16 bytes at a time.  This behaviour is not specified
in the SFP MSAs, which specifies:

 "The serial interface uses the 2-wire serial CMOS E2PROM protocol
  defined for the ATMEL AT24C01A/02/04 family of components."

and

 "As long as the SFP+ receives an acknowledge, it shall serially clock
  out sequential data words. The sequence is terminated when the host
  responds with a NACK and a STOP instead of an acknowledge."

We must avoid breaking a read across a 16-bit quantity in the diagnostic
page, thankfully all 16-bit quantities in that page are naturally
aligned.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Reviewed-by: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
index 68c8fbf..8807a80 100644 (file)
--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -280,6 +280,7 @@ static int sfp_i2c_read(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
 {
        struct i2c_msg msgs[2];
        u8 bus_addr = a2 ? 0x51 : 0x50;
+       size_t this_len;
        int ret;
 
        msgs[0].addr = bus_addr;
@@ -291,11 +292,26 @@ static int sfp_i2c_read(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,
        msgs[1].len = len;
        msgs[1].buf = buf;
 
-       ret = i2c_transfer(sfp->i2c, msgs, ARRAY_SIZE(msgs));
-       if (ret < 0)
-               return ret;
+       while (len) {
+               this_len = len;
+               if (this_len > 16)
+                       this_len = 16;
 
-       return ret == ARRAY_SIZE(msgs) ? len : 0;
+               msgs[1].len = this_len;
+
+               ret = i2c_transfer(sfp->i2c, msgs, ARRAY_SIZE(msgs));
+               if (ret < 0)
+                       return ret;
+
+               if (ret != ARRAY_SIZE(msgs))
+                       break;
+
+               msgs[1].buf += this_len;
+               dev_addr += this_len;
+               len -= this_len;
+       }
+
+       return msgs[1].buf - (u8 *)buf;
 }
 
 static int sfp_i2c_write(struct sfp *sfp, bool a2, u8 dev_addr, void *buf,