Subject: Re: [PATCH net,stable] phy: sfp: fix high power modules without diag mode

From: Bjørn Mork <[email-masked]>
Date: Fri, 03 Dec 2021 14:55:17 +0100

"Russell King (Oracle)" <[email-masked]> writes:

> Thinking a little more, how about this:
>
>  drivers/net/phy/sfp.c | 25 +++++++++++++++++++++----
>  1 file changed, 21 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/net/phy/sfp.c b/drivers/net/phy/sfp.c
> index 51a1da50c608..4c900d063b19 100644
> --- a/drivers/net/phy/sfp.c
> +++ b/drivers/net/phy/sfp.c
> @@ -1752,17 +1752,20 @@ static int sfp_sm_probe_for_phy(struct sfp *sfp)
>  static int sfp_module_parse_power(struct sfp *sfp)
>  {
>  	u32 power_mW = 1000;
> +	bool supports_a2;
>  
>  	if (sfp->id.ext.options & cpu_to_be16(SFP_OPTIONS_POWER_DECL))
>  		power_mW = 1500;
>  	if (sfp->id.ext.options & cpu_to_be16(SFP_OPTIONS_HIGH_POWER_LEVEL))
>  		power_mW = 2000;
>  
> +	supports_a2 = sfp->id.ext.sff8472_compliance !=
> +				SFP_SFF8472_COMPLIANCE_NONE ||
> +		      sfp->id.ext.diagmon & SFP_DIAGMON_DDM;
> +
>  	if (power_mW > sfp->max_power_mW) {
>  		/* Module power specification exceeds the allowed maximum. */
> -		if (sfp->id.ext.sff8472_compliance ==
> -			SFP_SFF8472_COMPLIANCE_NONE &&
> -		    !(sfp->id.ext.diagmon & SFP_DIAGMON_DDM)) {
> +		if (!supports_a2) {
>  			/* The module appears not to implement bus address
>  			 * 0xa2, so assume that the module powers up in the
>  			 * indicated mode.
> @@ -1779,11 +1782,24 @@ static int sfp_module_parse_power(struct sfp *sfp)
>  		}
>  	}
>  
> +	if (power_mW <= 1000) {
> +		/* Modules below 1W do not require a power change sequence */
> +		return 0;
> +	}
> +
> +	if (!supports_a2) {
> +		/* The module power level is below the host maximum and the
> +		 * module appears not to implement bus address 0xa2, so assume
> +		 * that the module powers up in the indicated mode.
> +		 */
> +		return 0;
> +	}
> +
>  	/* If the module requires a higher power mode, but also requires
>  	 * an address change sequence, warn the user that the module may
>  	 * not be functional.
>  	 */
> -	if (sfp->id.ext.diagmon & SFP_DIAGMON_ADDRMODE && power_mW > 1000) {
> +	if (sfp->id.ext.diagmon & SFP_DIAGMON_ADDRMODE) {
>  		dev_warn(sfp->dev,
>  			 "Address Change Sequence not supported but module requires %u.%uW, module may not be functional\n",
>  			 power_mW / 1000, (power_mW / 100) % 10);

Looks nice to me at least.  But I don't have the hardware to test it.

Bjørn