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

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Message-ID: <c687a7b4-24eb-f088-d6d0-f167a8f9da1f@gmail.com>
Date:   Thu, 30 Sep 2021 16:04:41 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Rafał Miłecki <zajec5@...il.com>,
        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 9/30/21 7:29 AM, Rafał Miłecki wrote:
> 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?

Thanks for providing the background.

You still appear to be needing an of_node_put() after
of_mdiobus_register() because that function does increase the reference
count.
-- 
Florian