RE: [PATCH] net/ixgbe: Retry SFP ID read field to handle misbehaving SFPs

["Wang, Haiyue" <haiyue.wang@intel.com>]

> -----Original Message-----
> From: jeffd@silicom-usa.com <jeffd@silicom-usa.com>
> Sent: Tuesday, March 8, 2022 06:34
> To: dev@dpdk.org
> Cc: Stephen Douthit <stephend@silicom-usa.com>; Daly, Jeff <jeffd@silicom-usa.com>; Wang, Haiyue
> <haiyue.wang@intel.com>
> Subject: [PATCH] net/ixgbe: Retry SFP ID read field to handle misbehaving SFPs
> 
> From: Stephen Douthit <stephend@silicom-usa.com>
> 
> Some XGS-PON SFPs have been observed ACKing I2C reads and returning
> uninitialized garbage while their uC boots.  This can lead to the SFP ID
> code marking an otherwise working SFP module as unsupported if a bogus
> ID value is read while its internal PHY/microcontroller is still
> booting.
> 
> Retry the ID read several times looking not just for NAK, but also for a
> valid ID field.
> 
> Since the device isn't NAKing the trasanction the existing longer retry
> code in ixgbe_read_i2c_byte_generic_int() doesn't apply here.
> 
> Signed-off-by: Stephen Douthit <stephend@silicom-usa.com>
> Signed-off-by: Jeff Daly <jeffd@silicom-usa.com>
> ---
>  drivers/net/ixgbe/base/ixgbe_phy.c | 31 ++++++++++++++++++++++++++----
>  1 file changed, 27 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/net/ixgbe/base/ixgbe_phy.c b/drivers/net/ixgbe/base/ixgbe_phy.c
> index d8d51d2c3f..27bce066a1 100644
> --- a/drivers/net/ixgbe/base/ixgbe_phy.c
> +++ b/drivers/net/ixgbe/base/ixgbe_phy.c
> @@ -1275,6 +1275,7 @@ s32 ixgbe_identify_sfp_module_generic(struct ixgbe_hw *hw)
>  	u8 cable_tech = 0;
>  	u8 cable_spec = 0;
>  	u16 enforce_sfp = 0;
> +	u8 id_reads;

"u8 retries" is a better name, I think, to match the patch title.

> 
>  	DEBUGFUNC("ixgbe_identify_sfp_module_generic");
> 
> @@ -1287,12 +1288,34 @@ s32 ixgbe_identify_sfp_module_generic(struct ixgbe_hw *hw)
>  	/* LAN ID is needed for I2C access */
>  	hw->mac.ops.set_lan_id(hw);
> 
> -	status = hw->phy.ops.read_i2c_eeprom(hw,
> -					     IXGBE_SFF_IDENTIFIER,
> -					     &identifier);
> +	/* Need to check this a couple of times for a sane value.
> +	 *
> +	 * SFPs that have a uC slaved to the I2C bus (vs. a dumb EEPROM) can be
> +	 * poorly designed such that they will ACK I2C reads and return
> +	 * whatever bogus data is in the SRAM (or whatever is backing the target
> +	 * device) before things are truly initialized.
> +	 *
> +	 * In a perfect world devices would NAK I2C requests until they were
> +	 * sane, but here we are.
> +	 *
> +	 * Give such devices a couple tries to get their act together before
> +	 * marking the device as unsupported.
> +	 */
> +	for (id_reads = 0; id_reads < 5; id_reads++) {
> +		status = hw->phy.ops.read_i2c_eeprom(hw,
> +						     IXGBE_SFF_IDENTIFIER,
> +						     &identifier);
> 
> -	if (status != IXGBE_SUCCESS)
> +		DEBUGOUT("status %d, id %d\n", status, identifier);
> +		if (!status &&
> +		    identifier == IXGBE_SFF_IDENTIFIER_SFP)

Let's not assume the ' IXGBE_SUCCESS' is '0', so change it to:

		if (status == IXGBE_SUCCESS &&
                identifier == IXGBE_SFF_IDENTIFIER_SFP)

> +			break;
> +	}
> +
> +	if (status != IXGBE_SUCCESS) {
> +		DEBUGOUT("Failed SFF ID read (%d attempts)\n", id_reads);
>  		goto err_read_i2c_eeprom;
> +	}
> 
>  	if (identifier != IXGBE_SFF_IDENTIFIER_SFP) {
>  		hw->phy.type = ixgbe_phy_sfp_unsupported;
> --
> 2.25.1