Re: [PATCH net-next 2/2] net: fixed_phy: set is_gigabit_capable member when needed

From: Heiner Kallweit <hkallweit1@gmail.com>
To: Marek Behun <marek.behun@nic.cz>, Andrew Lunn <andrew@lunn.ch>
Cc: netdev@vger.kernel.org,
	Sebastian Reichel <sebastian.reichel@collabora.co.uk>,
	Vivien Didelot <vivien.didelot@gmail.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	"David S . Miller" <davem@davemloft.net>
Subject: Re: [PATCH net-next 2/2] net: fixed_phy: set is_gigabit_capable member when needed
Date: Sun, 11 Aug 2019 18:59:12 +0200	[thread overview]
Message-ID: <76dc0ce2-238b-b27a-fff5-5fd633518cc0@gmail.com> (raw)
In-Reply-To: <20190811180815.024870da@nic.cz>

On 11.08.2019 18:08, Marek Behun wrote:
> On Sun, 11 Aug 2019 17:40:01 +0200
> Andrew Lunn <andrew@lunn.ch> wrote:
> 
>> On Sun, Aug 11, 2019 at 05:08:12PM +0200, Marek Behún wrote:
>>> The fixed_phy driver does not set the phydev->is_gigabit_capable member
>>> when the fixed_phy is gigabit capable.  
>>
>> Neither does any other PHY driver. It should be possible to tell if a
>> PHY supports 1G by looking at register values. If this does not work
>> for fixed_link, it means we are missing something in the emulation.
>> That is what we should be fixing.
>>
>> Also, this change has nothing to do the lp_advertise, what you
>> previously said the problem was. At the moment, i don't get the
>> feeling you have really dug all the way down and really understand the
>> root causes.
>>
>>      Andrew
> 
> Andrew,
> is_gigabit_capable is otherwise set only in the phy_probe function.
> This function is not called at all for the DSA cpu port fixed_link phy.
> Why is that? But I guess it is not important anymore, if CPU and DSA
> were converted to phylink in net-next. I shall test it and let you know.
> In any case, sorry for the spam.
> Marek
> 

A fixed phy should be bound to the genphy driver, but that happens later
in phy_attach_direct(). Maybe the fixed phy device of a CPU port gets
never attached to a net device? This would explain why phy_probe()
doesn't get called.
Following idea: We could swphy let return PHY ID 0xffffffff
(instead of current value 0x00000000). Then the fixed phy device would
be bound to the genphy driver immediately at device registration time.
As a consequence phy_probe() would call genphy_read_abilities() that
sets supported modes properly. This should allow to remove the manual
adding of supported modes in dsa_port_fixed_link_register_of().

One more thing regarding genphy_read_abilities() and fixed phys in general:
swphy sets bit BMSR_ESTATEN, then genphy_read_abilities() reads
MII_ESTATUS to check if and which 1Gbps modes are supported.
MII_ESTATUS however isn't defined in swphy. We're just fortunate
that therefore the default value 0xffff is returned and both
1Gbps modes seem to be supported.

Last but not least I think the calls to genphy_config_init() and
genphy_read_status() in dsa_port_fixed_link_register_of() are
both not needed and could be removed.

Heiner