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Date:   Wed, 13 Jan 2021 21:01:00 -0800 (PST)
From:   Palmer Dabbelt <palmer@...belt.com>
To:     sagar.kadam@...ive.com
CC:     linux-kernel@...r.kernel.org, linux-riscv@...ts.infradead.org,
        devicetree@...r.kernel.org, kernel@...il.dk,
        Atish Patra <Atish.Patra@....com>,
        Alistair Francis <Alistair.Francis@....com>,
        anup@...infault.org, yash.shah@...ive.com, aou@...s.berkeley.edu,
        Paul Walmsley <paul.walmsley@...ive.com>, robh+dt@...nel.org,
        sagar.kadam@...ive.com
Subject:     Re: [PATCH v2 0/3] fix macb phy probe failure if phy-reset is not handled

On Tue, 10 Nov 2020 07:22:09 PST (-0800), sagar.kadam@...ive.com wrote:
> HiFive Unleashed is having VSC8541-01 ethernet phy device and requires a
> specific reset sequence of 0-1-0-1 in order to use it in unmanaged mode.
> This series addresses a corner case where phy reset is not handled by boot
> stages prior to linux.
> Somewhat similar unreliable phy probe failure was reported and discussed
> here [1].
> The macb driver fails to detect the ethernet phy device if the bootloader
> doesn't provide a proper reset sequence to the phy device or the phy itself
> is in some invalid state. Currently, the FSBL or u-boot-spl is resetting
> the phy device, and so there is no issue observed in the linux network
> setup.
>
> The series is based on linux-5.10-rc5.
> Patch 1: Add the OUI to the phy dt node to fix issue of missing mdio device
> Patch 2 and 3:
> 	Resetting phy needs GPIO support so add to dt and defconfig.
>
> [1] https://lkml.org/lkml/2018/11/29/154
>
> To reproduce the issue:
> Using FSBL:
> 1. Comment out VSC8541 reset sequence in fsbl/main.c
>    from within the freedom-u540-c000-bootloader.
> 2. Build and flash fsbl.bin to micro sdcard.
>
> Using u-boot:
> 1. Comment out VSC8541 reset sequence in board/sifive/fu540/spl.c
>    from mainline u-boot source code.
> 2. Build and flash u-boot binaries to micro sdcard.
>
> Boot the board and bootlog will show network setup failure messages as:
>
> [  1.069474] libphy: MACB_mii_bus: probed
> [  1.073092] mdio_bus 10090000.ethernet-ffffffff: MDIO device at address 0
> 	       is missing
> .....
> [  1.979252] macb 10090000.ethernet eth0: Could not attach PHY (-19)
>
> 3. Now apply the series build, and boot kernel.
> 4. MACB and VSC8541 driver get successfully probed and the network is set
>    without any failure.
>
>
> So irrespective of whether the prior stages handle the phy reset sequence,
> the probing is successful in both the cases of cold boot and warm boot.
>
> Change History:
> ===============================
> V2:
> -Rebased v1 on linux kernel v5.10-rc3.
>
> V1:
> -Ignore 4th patch as suggested and so removed it from the series.
> -Verified this series on 5.7-rc5.
>
> V0: Base RFC patch. Verified on 5.7-rc2
>
> Sagar Shrikant Kadam (3):
>   dts: phy: fix missing mdio device and probe failure of vsc8541-01
>     device
>   dts: phy: add GPIO number and active state used for phy reset
>   riscv: defconfig: enable gpio support for HiFive Unleashed
>
>  arch/riscv/boot/dts/sifive/hifive-unleashed-a00.dts | 2 ++
>  arch/riscv/configs/defconfig                        | 2 ++
>  2 files changed, 4 insertions(+)

David pointed out I missed these, they're on fixes.  Thanks!

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