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Subject[PATCH 4.19 10/51] net: sfp: read eeprom in maximum 16 byte increments
Date
From: Russell King <rmk+kernel@armlinux.org.uk>

[ 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>
---
drivers/net/phy/sfp.c | 24 ++++++++++++++++++++----
1 file changed, 20 insertions(+), 4 deletions(-)

--- a/drivers/net/phy/sfp.c
+++ b/drivers/net/phy/sfp.c
@@ -280,6 +280,7 @@ static int sfp_i2c_read(struct sfp *sfp,
{
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,
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,

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