netdev - Re: [PATCH v2 12/12] [UNTESTED] riscv: dts: starfive: beaglev-starlight: Enable gmac

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Message-ID: <054bbf2a-e7ba-40bf-8f8b-f0e0e9b396c6@collabora.com>
Date: Tue, 28 Nov 2023 17:47:54 +0200
From: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
To: Emil Renner Berthing <emil.renner.berthing@...onical.com>,
 "David S. Miller" <davem@...emloft.net>, Eric Dumazet <edumazet@...gle.com>,
 Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
 Rob Herring <robh+dt@...nel.org>,
 Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
 Conor Dooley <conor+dt@...nel.org>, Emil Renner Berthing <kernel@...il.dk>,
 Samin Guo <samin.guo@...rfivetech.com>,
 Paul Walmsley <paul.walmsley@...ive.com>, Palmer Dabbelt
 <palmer@...belt.com>, Albert Ou <aou@...s.berkeley.edu>,
 Alexandre Torgue <alexandre.torgue@...s.st.com>,
 Jose Abreu <joabreu@...opsys.com>,
 Maxime Coquelin <mcoquelin.stm32@...il.com>,
 Richard Cochran <richardcochran@...il.com>,
 Giuseppe Cavallaro <peppe.cavallaro@...com>
Cc: netdev@...r.kernel.org, devicetree@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
 linux-stm32@...md-mailman.stormreply.com,
 linux-arm-kernel@...ts.infradead.org, kernel@...labora.com
Subject: Re: [PATCH v2 12/12] [UNTESTED] riscv: dts: starfive:
 beaglev-starlight: Enable gmac

On 11/28/23 14:08, Emil Renner Berthing wrote:
> Cristian Ciocaltea wrote:
>> On 11/26/23 23:10, Emil Renner Berthing wrote:
>>> Cristian Ciocaltea wrote:
>>>> The BeagleV Starlight SBC uses a Microchip KSZ9031RNXCA PHY supporting
>>>> RGMII-ID.
>>>>
>>>> TODO: Verify if manual adjustment of the RX internal delay is needed. If
>>>> yes, add the mdio & phy sub-nodes.
>>>
>>> Sorry for being late here. I've tested that removing the mdio and phy nodes on
>>> the the Starlight board works fine, but the rx-internal-delay-ps = <900>
>>> property not needed on any of my VisionFive V1 boards either.
>>
>> No problem, thanks a lot for taking the time to help with the testing!
>>
>>> So I wonder why you need that on your board
>>
>> I noticed you have a patch 70ca054e82b5 ("net: phy: motorcomm: Disable
>> rgmii rx delay") in your tree, hence I you please confirm the tests were
>> done with that commit reverted?
>>
>>> Also in the driver patch you add support for phy-mode = "rgmii-txid", but here
>>> you still set it to "rgmii-id", so which is it?
>>
>> Please try with "rgmii-id" first. I added "rgmii-txid" to have a
>> fallback solution in case the former cannot be used.
> 
> Ah, I see. Sorry I should have read up on the whole thread. Yes, the Starlight
> board with the Microchip phy works with "rgmii-id" as is. And you're right,
> with "rgmii-id" my VF1 needs the rx-internal-delay-ps = <900> property too.

That's great, we have now a pretty clear indication that this uncommon behavior
stems from the Motorcomm PHY, and *not* from GMAC.

>>
>>> You've alse removed the phy reset gpio on the Starlight board:
>>>
>>>   snps,reset-gpios = <&gpio 63 GPIO_ACTIVE_LOW>
>>>
>>> Why?
>>
>> I missed this in v1 as the gmac handling was done exclusively in
>> jh7100-common. Thanks for noticing!
>>
>>>>
>>>> Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@...labora.com>
>>>> ---
>>>>  arch/riscv/boot/dts/starfive/jh7100-beaglev-starlight.dts | 5 +++++
>>>>  1 file changed, 5 insertions(+)
>>>>
>>>> diff --git a/arch/riscv/boot/dts/starfive/jh7100-beaglev-starlight.dts b/arch/riscv/boot/dts/starfive/jh7100-beaglev-starlight.dts
>>>> index 7cda3a89020a..d3f4c99d98da 100644
>>>> --- a/arch/riscv/boot/dts/starfive/jh7100-beaglev-starlight.dts
>>>> +++ b/arch/riscv/boot/dts/starfive/jh7100-beaglev-starlight.dts
>>>> @@ -11,3 +11,8 @@ / {
>>>>  	model = "BeagleV Starlight Beta";
>>>>  	compatible = "beagle,beaglev-starlight-jh7100-r0", "starfive,jh7100";
>>>>  };
>>>> +
>>>> +&gmac {
>>>> +	phy-mode = "rgmii-id";
>>>> +	status = "okay";
>>>> +};
>>>
>>> Lastly the phy-mode and status are the same for the VF1 and Starlight boards,
>>> so why can't these be set in the jh7100-common.dtsi?
>>
>> I wasn't sure "rgmii-id" can be used for both boards and I didn't want
>> to unconditionally enable gmac on Starlight before getting a
>> confirmation that this actually works.
>>
>> If there is no way to make it working with "rgmii-id" (w/ or w/o
>> adjusting rx-internal-delay-ps), than we should switch to "rgmii-txid".
> 
> Yeah, I don't exactly know the difference, but both boards seem to work fine
> with "rgmii-id", so if that is somehow better and/or more correct let's just go
> with that.

As Andrew already pointed out, going with "rgmii-id" would be the recommended
approach, as this passes the responsibility of adding both TX and RX delays to
the PHY.  "rgmii-txid" requires the MAC to handle the RX delay, which might
break the boards having a conformant (aka well-behaving) PHY.  For some reason
the Microchip PHY seems to work fine in both cases, but that's most likely an
exception, as other PHYs might expose a totally different and undesired
behavior.

I will prepare a v3 soon, and will drop the patches you have already submitted
as part of [1].

Thanks again for your support, 
Cristian

[1]: https://lore.kernel.org/all/20231126232746.264302-1-emil.renner.berthing@canonical.com/