netdev - Re: [PATCH net-next + leds v2 6/7] net: phy: marvell: add support for LEDs controlled by Marvell PHYs

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Message-ID: <20200911124258.GB3390477@lunn.ch>
Date:   Fri, 11 Sep 2020 14:42:58 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Matthias Schiffer <matthias.schiffer@...tq-group.com>
Cc:     Marek Behún <marek.behun@....cz>,
        Pavel Machek <pavel@....cz>, netdev@...r.kernel.org,
        linux-leds@...r.kernel.org, Dan Murphy <dmurphy@...com>,
        Ondřej Jirman <megous@...ous.com>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next + leds v2 6/7] net: phy: marvell: add support
 for LEDs controlled by Marvell PHYs

> - Do all PHYs support manual setting of the LED level, or are the PHYs
> that can only work with HW triggers?

There are PHYs with do not have simple on/off.

> - Is setting PHY registers always efficiently possible, or should SW
> triggers be avoided in certain cases? I'm thinking about setups like
> mdio-gpio. I guess this can only become an issue for triggers that
> blink.

There are uses cases where not using software frequently writing
registers would be good. PTP time stamping is one, where the extra
jitter can reduce the accuracy of the clock.

I also think activity blinking in software is unlikely to be
accepted. Nothing extra is allowed in the hot path, when you can be
dealing with a million or more packets per second.

So i would say limit software fallback to link and speed, and don't
assume that is even possible depending on the hardware.

	Andrew