linux-kernel - Re: [PATCH v6 net-next 09/14] net: phy: marvell-88q2xxx: add cable test support

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Date: Thu, 15 Feb 2024 22:03:50 +0100
From: Dimitri Fedrau <dima.fedrau@...il.com>
To: Andrew Lunn <andrew@...n.ch>
Cc: Heiner Kallweit <hkallweit1@...il.com>,
	Russell King <linux@...linux.org.uk>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Stefan Eichenberger <eichest@...il.com>, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 net-next 09/14] net: phy: marvell-88q2xxx: add cable
 test support

Am Wed, Feb 14, 2024 at 06:54:58PM +0100 schrieb Andrew Lunn:
> > +static int mv88q222x_cable_test_get_status(struct phy_device *phydev,
> > +					   bool *finished)
> > +{
> > +	int ret;
> > +	u32 dist;
> > +
> > +	ret = phy_read_mmd(phydev, MDIO_MMD_PCS, MDIO_MMD_PCS_MV_TDR_STATUS);
> > +	if (ret < 0)
> > +		return ret;
> > +
> > +	*finished = true;
> 
> That looks odd. Is there no status bit which says it has completed? Is
> it guaranteed to complete within a fixed time? How is it guaranteed that
> mv88q222x_cable_test_get_status() is called at the necessary delay after 
> mv88q222x_cable_test_start()?
> 
According to the datasheet and the Marvell API bits(0:1) can be used to
check if the test has completed. Sample code waits 500ms before checking
the bits. If the test is not completed after the delay the corresponding
function returns with an error.

I just used bits(7:4) where 2'b1000 means that the test is in progress,
and setting *finished = false. I didn't introduced any delay, relying
on the reschedule delay of the PHY state machine. I didn't notice any
problems with this approach. Anyway if the test does not complete for
whatever reasons we get stuck here, right ? Don't know if this can
happen. Probably we should take the safer path described in the Marvell
API.

Dimitri