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

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Date:   Fri, 6 Mar 2020 12:14:20 +0100
From:   Ahmad Fatoum <a.fatoum@...gutronix.de>
To:     Philippe Schenker <philippe.schenker@...adex.com>,
        "o.rempel@...gutronix.de" <o.rempel@...gutronix.de>,
        "andrew@...n.ch" <andrew@...n.ch>
Cc:     "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux@...linux.org.uk" <linux@...linux.org.uk>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-imx@....com" <linux-imx@....com>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "allison@...utok.net" <allison@...utok.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kstewart@...uxfoundation.org" <kstewart@...uxfoundation.org>
Subject: Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy_fixup

Hello Philippe,

On 3/6/20 10:46 AM, Philippe Schenker wrote:
> Hi Andrew and Ahmad, thanks for your comments. I totally forgot about
> those more specific phy-modes. But just because none of our driver
> supports that. Either the i.MX6 fec-driver as well as the micrel.c PHY
> driver supports this tags.
> What do you guys suggest then how I should implement that skew stuff?

I think implementing them in the Micrel driver would make sense.
When more specific skews are supplied, these are used.
If not, the rgmii_[tx]?id applies the appropriate timings for length matched
lines. Device trees matching your use case will then only have to specify
rgmii-txid. 

> The problem is that i.MX6 has an asynchronic skew of -100 to 900ps only
> enabling the PHY-delay on TXC and RXC is not in all cases within the
> RGMII timing specs. That's why I implemented this 'weird' numbers.

I am not too well-versed with this. What's an asynchronic skew?
A non-deterministic internal delay..? So, you try to be as accurate as
possible, so the skew is within the acceptable margin?

Cheers
Ahmad


> 
> Philippe
> 

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