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);