linux-kernel - Re: [PATCH] arm64: dts: allwinner: a64: pine64-plus: Add PHY regulator delay

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Message-ID: <20190827134806.5l7dxyvzjrvabh7o@core.my.home>
Date:   Tue, 27 Aug 2019 15:48:06 +0200
From:   Ondřej Jirman <megous@...ous.com>
To:     Maxime Ripard <mripard@...nel.org>
Cc:     Jernej Skrabec <jernej.skrabec@...l.net>, wens@...e.org,
        robh+dt@...nel.org, mark.rutland@....com,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH] arm64: dts: allwinner: a64: pine64-plus: Add PHY
 regulator delay

Hi,

On Tue, Aug 27, 2019 at 03:34:43PM +0200, Maxime Ripard wrote:
> On Sun, Aug 25, 2019 at 03:03:36PM +0200, Jernej Skrabec wrote:
> > Depending on kernel and bootloader configuration, it's possible that
> > Realtek ethernet PHY isn't powered on properly. It needs some time
> > before it can be used.
> >
> > Fix that by adding 100ms ramp delay to regulator responsible for
> > powering PHY.
> >
> > Fixes: 94dcfdc77fc5 ("arm64: allwinner: pine64-plus: Enable dwmac-sun8i")
> > Suggested-by: Ondrej Jirman <megous@...ous.com>
> > Signed-off-by: Jernej Skrabec <jernej.skrabec@...l.net>
> 
> How was that delay found?

I suggested it. There's no delay in the dwmac-sun8i driver, so after enabling
the phy power, it will start accessing it over MDIO right away, which is not
good.

I suggested the value based on post-reset delay in the PHY's datasheet (30ms).
Multiplied ~3x (if I remember correctly) to get some safety margin. Chip has
more to do then after the HW reset, and regulator also needs some time to
ramp-up.

regards,
	o.

> It should at least have a comment explaining why it's there.
> 
> Thanks!
> Maxime
> 
> --
> Maxime Ripard, Bootlin
> Embedded Linux and Kernel engineering
> https://bootlin.com