netdev - Re: [PATCH net-next] net: phy: meson-gxl: support more G12A-internal PHY versions

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Message-ID: <e75ed56f-ba25-f337-e879-33cc2a784740@gmail.com>
Date:   Thu, 19 Jan 2023 23:42:54 +0100
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Neil Armstrong <neil.armstrong@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Jerome Brunet <jbrunet@...libre.com>,
        Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Cc:     Russell King - ARM Linux <linux@...linux.org.uk>,
        David Miller <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Kevin Hilman <khilman@...libre.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "open list:ARM/Amlogic Meson..." <linux-amlogic@...ts.infradead.org>
Subject: Re: [PATCH net-next] net: phy: meson-gxl: support more G12A-internal
 PHY versions

On 15.01.2023 21:38, Heiner Kallweit wrote:
> On 15.01.2023 19:43, Neil Armstrong wrote:
>> Hi Heiner,
>>
>> Le 15/01/2023 à 18:09, Heiner Kallweit a écrit :
>>> On 15.01.2023 17:57, Andrew Lunn wrote:
>>>> On Sun, Jan 15, 2023 at 04:19:37PM +0100, Heiner Kallweit wrote:
>>>>> On my SC2-based system the genphy driver was used because the PHY
>>>>> identifies as 0x01803300. It works normal with the meson g12a
>>>>> driver after this change.
>>>>> Switch to PHY_ID_MATCH_MODEL to cover the different sub-versions.
>>>>
>>>> Hi Heiner
>>>>
>>>> Are there any datasheets for these devices? Anything which documents
>>>> the lower nibble really is a revision?
>>>>
>>>> I'm just trying to avoid future problems where we find it is actually
>>>> a different PHY, needs its own MATCH_EXACT entry, and then we find we
>>>> break devices using 0x01803302 which we had no idea exists, but got
>>>> covered by this change.
>>>>
>>> The SC2 platform inherited a lot from G12A, therefore it's plausible
>>> that it's the same PHY. Also the vendor driver for SC2 gives a hint
>>> as it has the following compatible for the PHY:
>>>
>>> compatible = "ethernet-phy-id0180.3301", "ethernet-phy-ieee802.3-c22";
>>>
>>> But you're right, I can't say for sure as I don't have the datasheets.
>>
>> On G12A (& GXL), the PHY ID is set in the MDIO MUX registers,
>> please see:
>> https://elixir.bootlin.com/linux/latest/source/drivers/net/mdio/mdio-mux-meson-g12a.c#L36
>>
>> So you should either add support for the PHY mux in SC2 or check
>> what is in the ETH_PHY_CNTL0 register.
>>
> Thanks for the hint. I just checked and reading back ETH_PHY_CNTL0 at the
> end of g12a_enable_internal_mdio() gives me the expected result of 0x33010180.
> But still the PHY reports 3300.
> Even if I write some other random value to ETH_PHY_CNTL0, I get 0180/3300
> as PHY ID.
> 
> For u-boot I found the following:
> 
> https://github.com/khadas/u-boot/blob/khadas-vim4-r-64bit/drivers/net/phy/amlogic.c
> 
> static struct phy_driver amlogic_internal_driver = {
> 	.name = "Meson GXL Internal PHY",
> 	.uid = 0x01803300,
> 	.mask = 0xfffffff0,
> 	.features = PHY_BASIC_FEATURES,
> 	.config = &meson_phy_config,
> 	.startup = &meson_aml_startup,
> 	.shutdown = &genphy_shutdown,
> };
> 
> So it's the same PHY ID I'm seeing in Linux.
> 
> My best guess is that the following is the case:
> 
> The PHY compatible string in DT is the following in all cases:
> compatible = "ethernet-phy-id0180.3301", "ethernet-phy-ieee802.3-c22";
> 
> Therefore id 0180/3301 is used even if the PHY reports something else.
> Means it doesn't matter which value you write to ETH_PHY_CNTL0.
> 
> I reduced the compatible string to compatible = "ethernet-phy-ieee802.3-c22"
> and this resulted in the actual PHY ID being used.
> You could change the compatible in dts the same way for any g12a system
> and I assume you would get 0180/3300 too.
> 
> Remaining question is why the value in ETH_PHY_CNTL0 is ignored.
> 

I think I found what's going on. The PHY ID written to SoC register
ETH_PHY_CNTL0 isn't effective immediately. It takes a PHY soft reset before
it reports the new PHY ID. Would be good to have a comment in the
g12a mdio mux code mentioning this constraint.

I see no easy way to trigger a soft reset early enough. Therefore it's indeed
the simplest option to specify the new PHY ID in the compatible.