linux-kernel - Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy

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Date:   Fri, 6 Mar 2020 08:42:47 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>,
        Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Kate Stewart <kstewart@...uxfoundation.org>,
        Fabio Estevam <festevam@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Russell King <linux@...linux.org.uk>,
        linux-kernel@...r.kernel.org,
        Philippe Schenker <philippe.schenker@...adex.com>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        Thomas Gleixner <tglx@...utronix.de>,
        Shawn Guo <shawnguo@...nel.org>,
        Allison Randal <allison@...utok.net>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy_fixup

Hello Andrew,

On 3/5/20 5:51 PM, Andrew Lunn wrote:
> On Thu, Mar 05, 2020 at 03:38:05PM +0100, Oleksij Rempel wrote:
>> Hi Philippe,
>>
>> On Thu, Mar 05, 2020 at 02:49:28PM +0100, Philippe Schenker wrote:
>>> The MAC of the i.MX6 SoC is compliant with RGMII v1.3. The KSZ9131 PHY
>>> is like KSZ9031 adhering to RGMII v2.0 specification. This means the
>>> MAC should provide a delay to the TXC line. Because the i.MX6 MAC does
>>> not provide this delay this has to be done in the PHY.
>>>
>>> This patch adds by default ~1.6ns delay to the TXC line. This should
>>> be good for all boards that have the RGMII signals routed with the
>>> same length.
>>>
>>> The KSZ9131 has relatively high tolerances on skew registers from
>>> MMD 2.4 to MMD 2.8. Therefore the new DLL-based delay of 2ns is used
>>> and then as little as possibly subtracted from that so we get more
>>> accurate delay. This is actually needed because the i.MX6 SoC has
>>> an asynchron skew on TXC from -100ps to 900ps, to get all RGMII
>>> values within spec.
>>
>> This configuration has nothing to do in mach-imx/* It belongs to the
>> board devicetree. Please see DT binding documentation for needed
>> properties:
>> Documentation/devicetree/bindings/net/micrel-ksz90x1.txt
> 
> It probably does not even need that. Just
> 
> phy-mode = <rgmii-txid>

Looks to me like this isn't supported by the Micrel PHY driver or am
I missing something?

Cheers
Ahmad

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