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

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Date:   Thu, 1 Jun 2023 11:10:58 +0200
From:   Andreas Svensson <andreas.svensson@...s.com>
To:     Andrew Lunn <andrew@...n.ch>
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 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 know there are some users who want the switch to boot as fast as
> possible, and don't really want the additional 9ms delay. But this is
> also a legitimate change. I'm just wondering if we need to consider a
> DT property here for those with EEPROM content. Or, if there is an
> interrupt line, wait for the EEPROM complete interrupt. We just have
> tricky chicken and egg problems. At this point in time, we don't
> actually know if the devices exists or not.
> 
> 	  Andrew

It just seems like we need to wait longer for the switch 88E6393X
until it responds reliably on the MDIO bus. But I'm open to adding
a new DT property if that's needed.

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.

Best Regards,
Andreas Svensson