linux-kernel - Aw: Re: [RFC v1 1/3] net: dsa: mt753x: make reset optional

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Date:   Wed, 27 Apr 2022 09:05:34 +0200
From:   Frank Wunderlich <frank-w@...lic-files.de>
To:     Vladimir Oltean <olteanv@...il.com>
Cc:     Frank Wunderlich <linux@...web.de>,
        linux-mediatek@...ts.infradead.org,
        linux-rockchip@...ts.infradead.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Heiko Stuebner <heiko@...ech.de>,
        Sean Wang <sean.wang@...iatek.com>,
        Landen Chao <Landen.Chao@...iatek.com>,
        DENG Qingfang <dqfext@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Peter Geis <pgwipeout@...il.com>, devicetree@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Aw: Re: [RFC v1 1/3] net: dsa: mt753x: make reset optional

Hi,

you're right, reset is already optional...

idk why it was failing before the patch...i guess i had always defined the reset in dts on switch-side and dropped it same time with this patch.

Reset on both nodes (gmac+switch) blocks in switch driver because of exclusive (error message "could not get our reset line") and after dropping the reset on gmac-side the mdio-bus does not come up after switch driver resets gmac+switch (in loop with edefer).

> Gesendet: Mittwoch, 27. April 2022 um 01:57 Uhr
> Von: "Vladimir Oltean" <olteanv@...il.com>
> On Tue, Apr 26, 2022 at 03:49:22PM +0200, Frank Wunderlich wrote:
> > From: Frank Wunderlich <frank-w@...lic-files.de>
> >
> > Currently a reset line is required, but on BPI-R2-Pro board
> > this reset is shared with the gmac and prevents the switch to
> > be initialized because mdio is not ready fast enough after
> > the reset.
> >
> > So make the reset optional to allow shared reset lines.
>
> What does it mean "to allow shared reset lines"? Allow as in "allow them
> to sit there, unused"?

for switch part unused right, but reset-line is used by gmac. If switch does the reset, it resets the gmac too and so the mdio goes down. It took longer to get up than the wait-poll after the reset and so i got mdio read errors.

> > -	} else {
> > +	} else if (priv->reset) {
>
> I don't really understand this patch. gpiod_set_value_cansleep() can
> tolerate NULL GPIO descriptors.

had not looked for NULL-tolerance, so i precautionary added the check.

> >  		gpiod_set_value_cansleep(priv->reset, 0);
> >  		usleep_range(1000, 1100);
> >  		gpiod_set_value_cansleep(priv->reset, 1);

> > @@ -3272,8 +3272,7 @@ mt7530_probe(struct mdio_device *mdiodev)
> >  		priv->reset = devm_gpiod_get_optional(&mdiodev->dev, "reset",
> >  						      GPIOD_OUT_LOW);
> >  		if (IS_ERR(priv->reset)) {
> > -			dev_err(&mdiodev->dev, "Couldn't get our reset line\n");
> > -			return PTR_ERR(priv->reset);
> > +			dev_warn(&mdiodev->dev, "Couldn't get our reset line\n");
>
> I certainly don't understand why you're suppressing the pointer-encoded
> errors here. The function used is devm_gpiod_get_optional(), which
> returns NULL for a missing reset-gpios, not IS_ERR(something). The
> IS_ERR(something) is actually important to not ignore, maybe it's
> IS_ERR(-EPROBE_DEFER). And this change breaks waiting for the descriptor
> to become available.

you're right...the intention was to not leave the probe function if not reset was defined...but yes, devm_gpiod_get_optional is called so reset is already optional.

> So what doesn't work without this patch, exactly?

reverted the Patch in my repo and it is still working :)

just ignore it. something went wrong during my tests...

sorry for the inconvenience.

regards Frank