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Subject: Re: [PATCH net] net: broadcom: Imply BROADCOM_PHY for BCMGENET
To:     Florian Fainelli <f.fainelli@gmail.com>, netdev@vger.kernel.org
Cc:     nsaenzjulienne@suse.de, wahrenst@gmx.net,
        "David S. Miller" <davem@davemloft.net>,
        Thomas Gleixner <tglx@linutronix.de>,
        Tal Gilboa <talgi@mellanox.com>,
        Michael Chan <michael.chan@broadcom.com>,
        Geert Uytterhoeven <geert+renesas@glider.be>,
        Andy Gospodarek <gospo@broadcom.com>,
        Randy Dunlap <rdunlap@infradead.org>,
        open list <linux-kernel@vger.kernel.org>
From:   Marek Szyprowski <m.szyprowski@samsung.com>
Message-ID: <d4ddf75c-3355-daee-b1d1-8db02675507a@samsung.com>
Date:   Tue, 12 May 2020 08:00:12 +0200
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Hi Florian,

On 11.05.2020 20:19, Florian Fainelli wrote:
> On 5/11/2020 12:21 AM, Marek Szyprowski wrote:
>> On 09.05.2020 00:32, Florian Fainelli wrote:
>>> The GENET controller on the Raspberry Pi 4 (2711) is typically
>>> interfaced with an external Broadcom PHY via a RGMII electrical
>>> interface. To make sure that delays are properly configured at the PHY
>>> side, ensure that we get a chance to have the dedicated Broadcom PHY
>>> driver (CONFIG_BROADCOM_PHY) enabled for this to happen.
>>>
>>> Fixes: 402482a6a78e ("net: bcmgenet: Clear ID_MODE_DIS in EXT_RGMII_OOB_CTRL when not needed")
>>> Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>> Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
>>> ---
>>> David,
>>>
>>> I would like Marek to indicate whether he is okay or not with this
>>> change. Thanks!
>> It is better. It fixes the default values for ARM 32bit
>> bcm2835_defconfig and ARM 64bit defconfig, so you can add:
>>
>> Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
>>
>> There is still an issue there. In case of ARM 64bit, when Genet driver
>> is configured as a module, BROADCOM_PHY is also set to module. When I
>> changed Genet to be built-in, BROADCOM_PHY stayed selected as module.
> OK.
>
>> This case doesn't work, as Genet driver is loaded much earlier than the
>> rootfs/initrd/etc is available, thus broadcom phy driver is not loaded
>> at all. It looks that some kind of deferred probe is missing there.
> In the absence of a specific PHY driver the Generic PHY driver gets used
> instead. This is a valid situation as I described in my other email
> because the boot loader/firmware could have left the PHY properly
> configured with the expected RGMII delays and configuration such that
> Linux does not need to be aware of anything. I suppose we could change
> the GENET driver when running on the 2711 platform to reject the PHY
> driver being "Generic PHY" on the premise that a specialized driver
> should be used instead, but that seems a bit too restrictive IMHO.
>
> Do you prefer a "select BROADCOM_PHY if ARCH_BCM2835" then?

Yes. It solves the issue after switching Genet to be built-in without 
the need to change the CONFIG_BROADCOM_PHY.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland