netdev - Re: [PATCH net-next] net: bgmac: support MDIO described in DT

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Message-ID: <780a6e7f-655a-6d79-d086-2eefd7e9ccb6@gmail.com>
Date:   Thu, 30 Sep 2021 16:29:25 +0200
From:   Rafał Miłecki <zajec5@...il.com>
To:     Florian Fainelli <f.fainelli@...il.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, devicetree@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com,
        Rafał Miłecki <rafal@...ecki.pl>
Subject: Re: [PATCH net-next] net: bgmac: support MDIO described in DT

On 20.09.2021 19:57, Rafał Miłecki wrote:
> On 20.09.2021 18:11, Florian Fainelli wrote:
>> I believe this leaks np and the use case is not exactly clear to me
>> here. AFAICT the Northstar SoCs have two MDIO controllers: one for
>> internal PHYs and one for external PHYs which how you would attach a
>> switch to the chip (in chipcommonA). Is 53573 somewhat different here?
>> What is the MDIO bus driver that is being used?
> 
> of_get_child_by_name() doesn't seem to increase refcount or anything and
> I think it's how most drivers handle it. I don't think it should leak.
> 
> BCM53573 is a built with some older blocks. Please check:
> 
> 4ebd50472899 ("ARM: BCM53573: Initial support for Broadcom BCM53573 SoCs")
>      BCM53573 series is a new family with embedded wireless. By marketing
>      people it's sometimes called Northstar but it uses different CPU and has
>      different architecture so we need a new symbol for it.
>      Fortunately it shares some peripherals with other iProc based SoCs so we
>      will be able to reuse some drivers/bindings.
> 
> e90d2d51c412 ("ARM: BCM5301X: Add basic dts for BCM53573 based Tenda AC9")
>      BCM53573 seems to be low priced alternative for Northstar chipsts. It
>      uses single core Cortex-A7 and doesn't have SDU or local (TWD) timer. It
>      was also stripped out of independent SPI controller and 2 GMACs.
> 
> Northstar uses SRAB which is some memory based (0x18007000) access to
> switch register space.
> BCM53573 uses different blocks & mappings and it doesn't include SRAB at
> 0x18007000. Accessing switch registers is handled over MDIO.

Florian: did my explanations help reviewing this patch? Would you ack it
now?