linux-kernel - Re: [PATCH net] net: dsa: mv88e6xxx: Increase wait after reset deactivation

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Message-ID: <133860f9-e745-44ce-9b74-c5d990cf92db@lunn.ch>
Date:   Thu, 1 Jun 2023 14:01:52 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Andreas Svensson <andreas.svensson@...s.com>
Cc:     Florian Fainelli <f.fainelli@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>, kernel@...s.com,
        Baruch Siach <baruch@...s.co.il>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH net] net: dsa: mv88e6xxx: Increase wait after reset
 deactivation

 On Thu, Jun 01, 2023 at 11:10:58AM +0200, Andreas Svensson wrote:
> On 5/30/23 19:28, Andrew Lunn wrote:
> > On Tue, May 30, 2023 at 04:52:23PM +0200, Andreas Svensson wrote:
> > > A switch held in reset by default needs to wait longer until we can
> > > reliably detect it.
> > > 
> > > An issue was observed when testing on the Marvell 88E6393X (Link Street).
> > > The driver failed to detect the switch on some upstarts. Increasing the
> > > wait time after reset deactivation solves this issue.
> > > 
> > > The updated wait time is now also the same as the wait time in the
> > > mv88e6xxx_hardware_reset function.
> > 
> > Do you have an EEPROM attached and content in it?
> 
> There's no EEPROM attached to the switch in our design.
> 
> > 
> > It is not necessarily the reset itself which is the problem, but how
> > long it takes after the reset to read the contents of the
> > EEPROM. While it is doing that, is does not respond on the MDIO
> > bus. Which is why mv88e6xxx_hardware_reset() polls for that to
> > complete.
> 
> Ok, yes that makes sense. I could add the mv88e6xxx_g1_wait_eeprom_done
> function after the reset deactivation.

I don't think that works, because how to talk to the switch is not
determined until after the switch has been detected.

> The datasheet for 88E6393X also states that it needs at least 10ms
> before it's ready. But I suppose this varies from switch to switch.

O.K, let go with this change and see if anybody really complains. We
can always add a DT property later.

Reviewed-by: Andrew Lunn <andrew@...n.ch>

You probably need to repost with my Reviewed-by added, now that Paolo
has changed the status of the patch.

    Andrew