netdev - Re: [PATCH net-next] net: phy: switch drivers to use dynamic feature detection

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Message-ID: <bc5c192e-78ce-89b1-eeae-541836f5f0fb@gmail.com>
Date:   Mon, 8 Apr 2019 19:45:13 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        David Miller <davem@...emloft.net>,
        Ray Jui <rjui@...adcom.com>,
        Scott Branden <sbranden@...adcom.com>,
        Richard Cochran <richardcochran@...il.com>,
        Kevin Hilman <khilman@...libre.com>,
        Heiko Stuebner <heiko@...ech.de>,
        bcm-kernel-feedback-list@...adcom.com, netdev@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org
Subject: Re: [PATCH net-next] net: phy: switch drivers to use dynamic feature
 detection

On 08.04.2019 00:13, Andrew Lunn wrote:
> On Sun, Apr 07, 2019 at 11:57:13AM +0200, Heiner Kallweit wrote:
>> Recently genphy_read_abilities() has been added that dynamically detects
>> clause 22 PHY abilities. I *think* this detection should work with all
>> supported PHY's, at least for the ones with basic features sets, i.e.
>> PHY_BASIC_FEATURES and PHY_GBIT_FEATURES. So let's remove setting these
>> features explicitly and rely on phylib feature detection.
> 
> Hi Heiner
> 
Hi Andrew,

> We could make this a two step process, to avoid regressions. For one
> cycle compare genphy_read_abilities() against .features and raise a
> WARN_ON() if they differ. And keep using the .features value.
> 
in general this is a good idea. I say in general because this would fail
with several, if not most GBit PHY's. Reason is that the hardcoded
features currently pretend we're supporting 1000BT/Half, whilst several
PHY's don't support this mode. 1000BT/Half has been specified but never
really been used. If we see it from this angle, the series is actually
a fix. The feature detection uses very basic C22 registers/bits,
therefore I consider the risk of breaking something to be relatively low.
And just in case we have the rc phase to fix support for a broken PHY.

Splitting the series and waiting for a Tested-by, as proposed by Richard,
may be problematic because most PHY drivers don't have a dedicated
maintainer, and we lack the hardware to test.

> Then a release late, complete the swap removing .features and the
> WARN_ON.
> 
> 	Andrew
> .
> 
Heiner