linux-kernel - Re: [PATCH v1 1/5] phy: amlogic: during USB PHY clkin obtaining, enable it

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Message-ID: <20230417115707.p5btzzg4rlyzf7ni@CAB-WSD-L081021>
Date:   Mon, 17 Apr 2023 14:57:07 +0300
From:   Dmitry Rokosov <ddrokosov@...rdevices.ru>
To:     Martin Blumenstingl <martin.blumenstingl@...glemail.com>
CC:     <gregkh@...uxfoundation.org>, <robh+dt@...nel.org>,
        <krzysztof.kozlowski+dt@...aro.org>, <neil.armstrong@...aro.org>,
        <khilman@...libre.com>, <jbrunet@...libre.com>,
        <mturquette@...libre.com>, <vkoul@...nel.org>, <kishon@...nel.org>,
        <hminas@...opsys.com>, <Thinh.Nguyen@...opsys.com>,
        <yue.wang@...ogic.com>, <hanjie.lin@...ogic.com>,
        <kernel@...rdevices.ru>, <rockosov@...il.com>,
        <linux-usb@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-amlogic@...ts.infradead.org>,
        <linux-phy@...ts.infradead.org>
Subject: Re: [PATCH v1 1/5] phy: amlogic: during USB PHY clkin obtaining,
 enable it

On Sun, Apr 16, 2023 at 10:54:17PM +0200, Martin Blumenstingl wrote:
> Hi Dmitry,
> 
> On Fri, Apr 14, 2023 at 5:24 PM Dmitry Rokosov <ddrokosov@...rdevices.ru> wrote:
> [...]
> > -       priv->clk = devm_clk_get(dev, "xtal");
> > +       priv->clk = devm_clk_get_enabled(dev, "xtal");
> Generally this works fine but I wouldn't recommend this approach if:
> - there's some required wait time after the clock has been enabled
> (see phy_meson_g12a_usb2_init - there's already some required wait
> time after triggering the reset)
> - clock gating (for power saving) is needed when the dwc3 driver is
> unloaded by the PHY driver is not
> 
> In this case: just manually manage the clock in phy_meson_g12a_usb2_{init,exit}

I'm sorry, but I'm not fully understanding your point. Currently, no
sleeps are required for this clock and we don't have any logic for
power saving (g12a phy_ops doesn't have power_on()/power_off()
implementation).
However, I believe all of your arguments make sense for the future
development of the phy_meson_g12a_usb2 driver. Is that correct?

-- 
Thank you,
Dmitry