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

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Date:   Sat, 15 Jan 2022 17:58:43 +0100
From:   Christian Lamparter <chunkeey@...il.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     Bjørn Mork <bjorn@...k.no>,
        netdev@...r.kernel.org,
        照山周一郎 <teruyama@...ingboard-inc.jp>
Subject: Re: [PATCH net,stable] phy: sfp: fix high power modules without diag
 mode

On 03/12/2021 13:58, Russell King (Oracle) wrote:
> On Fri, Dec 03, 2021 at 11:54:57AM +0000, Russell King (Oracle) wrote:
> [...]
> 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);
>

The reporter has problems reaching you. But from what I can tell in his reply to his
OpenWrt Github PR:
<https://github.com/openwrt/openwrt/pull/4802#issuecomment-1013439827>

your approach is working perfectly. Could you spin this up as a fully-fledged patch (backports?)

Thank you & Cheers,
Christian