From: "Alvin Šipraga" <ALSI@bang-olufsen.dk>
To: Andrew Lunn <andrew@lunn.ch>
Cc: "Luiz Angelo Daros de Luca" <luizluca@gmail.com>,
"Alvin Šipraga" <alvin@pqrs.dk>,
"Linus Walleij" <linus.walleij@linaro.org>,
"Vivien Didelot" <vivien.didelot@gmail.com>,
"Florian Fainelli" <f.fainelli@gmail.com>,
"Vladimir Oltean" <olteanv@gmail.com>,
"David S. Miller" <davem@davemloft.net>,
"Jakub Kicinski" <kuba@kernel.org>,
"Michael Rasmussen" <MIR@bang-olufsen.dk>,
"Arınç ÜNAL" <arinc.unal@arinc9.com>,
"open list:NETWORKING DRIVERS" <netdev@vger.kernel.org>,
"open list" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH net-next 0/2] net: dsa: realtek: fix PHY register read corruption
Date: Wed, 16 Feb 2022 19:26:43 +0000 [thread overview]
Message-ID: <878ruasjd8.fsf@bang-olufsen.dk> (raw)
In-Reply-To: <Yg1MfpK5PwiAbGfU@lunn.ch> (Andrew Lunn's message of "Wed, 16 Feb 2022 20:11:58 +0100")
Andrew Lunn <andrew@lunn.ch> writes:
>> Hmm OK. Actually I'm a bit confused about the mdio_lock: can you explain
>> what it's guarding against, for someone unfamiliar with MDIO?
>
> The more normal use case for MDIO is for PHYs, not switches. There can
> be multiple PHYs on one MDIO bus. And these PHYs each have there own
> state machine in phylib. At any point in time, that state machine can
> request the driver to do something, like poll the PHY status, does it
> have link? To prevent two PHY drivers trying to use the MDIO bus at
> the same time, there is an MDIO lock. At the beginning of an MDIO
> transaction, the lock is taken. And the end of the transaction,
> reading or writing one register of a device on the bus, the lock is
> released.
>
> So the MDIO lock simply ensures there is only one user of the MDIO bus
> at one time, for a single read or write.
>
> For PHYs this is sufficient. For switches, sometimes you need
> additional protection. The granularity of an access might not be a
> single register read or a write. It could be you need to read or write
> a few registers in an atomic way. If that is the case, you need a lock
> at a higher level.
Thank you Andrew for the clear explanation.
Somewhat unrelated to this series, but are you able to explain to me the
difference between:
mutex_lock(&bus->mdio_lock);
and
mutex_lock_nested(&bus->mdio_lock, MDIO_MUTEX_NESTED);
While looking at other driver examples I noticed the latter form quite a
few times too.
Kind regards,
Alvin
next prev parent reply other threads:[~2022-02-16 19:26 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-16 16:04 [PATCH net-next 0/2] net: dsa: realtek: fix PHY register read corruption Alvin Šipraga
2022-02-16 16:04 ` [PATCH net-next 1/2] net: dsa: realtek: allow subdrivers to externally lock regmap Alvin Šipraga
2022-02-16 16:05 ` [PATCH net-next 2/2] net: dsa: realtek: rtl8365mb: serialize indirect PHY register access Alvin Šipraga
2022-02-16 23:39 ` Vladimir Oltean
2022-02-17 3:01 ` Luiz Angelo Daros de Luca
2022-02-17 8:16 ` Alvin Šipraga
2022-02-22 0:18 ` Luiz Angelo Daros de Luca
2022-02-17 7:41 ` Alvin Šipraga
2022-02-17 11:17 ` Vladimir Oltean
2022-02-17 12:51 ` Alvin Šipraga
2022-02-21 14:50 ` Alvin Šipraga
2022-02-21 17:15 ` Vladimir Oltean
2022-02-21 18:10 ` Alvin Šipraga
2022-02-16 17:57 ` [PATCH net-next 0/2] net: dsa: realtek: fix PHY register read corruption Luiz Angelo Daros de Luca
2022-02-16 18:23 ` Alvin Šipraga
2022-02-16 19:11 ` Andrew Lunn
2022-02-16 19:26 ` Alvin Šipraga [this message]
2022-02-17 12:12 ` Andrew Lunn
2022-02-17 13:09 ` Alvin Šipraga
2022-02-17 13:32 ` Andrew Lunn
2022-02-17 4:28 ` Luiz Angelo Daros de Luca
2022-02-17 7:53 ` Alvin Šipraga
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