netdev - Re: [PATCH net-next v2 2/2] net: phy: broadcom: Do not modify LED configuration for SFP module PHYs

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Date:   Tue, 16 Feb 2021 17:04:14 +0000
From:   Russell King - ARM Linux admin <linux@...linux.org.uk>
To:     Robert Hancock <robert.hancock@...ian.com>
Cc:     "bcm-kernel-feedback-list@...adcom.com" 
        <bcm-kernel-feedback-list@...adcom.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: [PATCH net-next v2 2/2] net: phy: broadcom: Do not modify LED
 configuration for SFP module PHYs

On Tue, Feb 16, 2021 at 04:52:13PM +0000, Robert Hancock wrote:
> On Sat, 2021-02-13 at 10:45 +0000, Russell King - ARM Linux admin wrote:
> > On Fri, Feb 12, 2021 at 08:18:40PM -0600, Robert Hancock wrote:
> > > +	if (!phydev->sfp_bus &&
> > > +	    (!phydev->attached_dev || !phydev->attached_dev->sfp_bus)) {
> > 
> > First, do we want this to be repeated in every driver?
> > 
> > Second, are you sure this is the correct condition to be using for
> > this?  phydev->sfp_bus is non-NULL when _this_ PHY has a SFP bus
> > connected to its fibre side, it will never be set for a PHY on a
> > SFP. The fact that it is non-NULL or NULL shouldn't have a bearing
> > on whether we configure the LED register.
> 
> I think you're correct, the phydev->sfp_bus portion is probably not useful and
> could be dropped. What we're really concerned about is whether this PHY is on
> an SFP module or not. I'm not sure that a module-specific quirk makes sense
> here since there are probably other models which have a similar design where
> the LED outputs from the PHY are used for other purposes, and there's really no
> benefit to playing with the LED outputs on SFP modules in any case, so it would
> be safer to skip the LED reconfiguration for anything on an SFP. So we could
> either have a condition for "!phydev->attached_dev || !phydev->attached_dev-
> >sfp_bus" here and anywhere else that needs a similar check, or we do something
> different, like have a specific flag to indicate that this PHY is on an SFP
> module? What do people think is best here?

I don't think relying on phydev->attached_dev in any way is a good
idea, and I suspect a flag is going to be way better. One of the
problems is that phydev->dev_flags are PHY specific at the moment.
Not sure if we can do anything about that.

In the short term, at the very least, I think we should wrap whatever
test we use in a "phy_on_sfp(phydev)" helper so that we have a standard
helper for this.

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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