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Subject: Re: [PATCH] ARM: mach-imx6q: add ksz9131rn_phy_fixup
To:     Philippe Schenker <philippe.schenker@toradex.com>,
        "o.rempel@pengutronix.de" <o.rempel@pengutronix.de>,
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From:   Ahmad Fatoum <a.fatoum@pengutronix.de>
Message-ID: <f47a46b9-6d6a-e257-4309-7e49852bc88e@pengutronix.de>
Date:   Fri, 6 Mar 2020 12:14:20 +0100
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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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