linux-kernel - Re: [RFCv1 7/8] phy: amlogic: meson8b-usb2: Power off the PHY by putting it into reset mode.

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Date:   Fri, 18 Jun 2021 00:37:02 +0200
From:   Martin Blumenstingl <martin.blumenstingl@...glemail.com>
To:     Anand Moon <linux.amoon@...il.com>
Cc:     Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>,
        Neil Armstrong <narmstrong@...libre.com>,
        Kevin Hilman <khilman@...libre.com>,
        Jerome Brunet <jbrunet@...libre.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        linux-phy@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-amlogic@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [RFCv1 7/8] phy: amlogic: meson8b-usb2: Power off the PHY by
 putting it into reset mode.

Hi Anand,

On Thu, Jun 17, 2021 at 9:44 PM Anand Moon <linux.amoon@...il.com> wrote:
[...]
> @@ -245,8 +250,6 @@ static int phy_meson8b_usb2_power_on(struct phy *phy)
>         regmap_update_bits(priv->regmap, REG_CTRL, REG_CTRL_FSEL_MASK,
>                            0x5 << REG_CTRL_FSEL_SHIFT);
>         /* reset the PHY */
> -       regmap_update_bits(priv->regmap, REG_CTRL, REG_CTRL_POWER_ON_RESET,
> -                          REG_CTRL_POWER_ON_RESET);
The vendor driver uses the following sequence for the power on reset:
- set the power on reset bit
- wait 500us
- clear the power on reset bit
- wait 500us

With your change we now:
- wait 500us
- clear the power on reset bit
- wait 500us

I don't know if this is sufficient to bring the PHY into a well-defined state.
Maybe it works, maybe it doesn't reset at all in this case - I don't
know how to verify this though.


Best regards,
Martin