netdev - Re: [PATCH net-next v5 1/5] rust: core abstractions for network PHY drivers

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Message-ID: <b58e0874-b0d4-4218-a457-4e2e753e0b17@lunn.ch>
Date: Fri, 20 Oct 2023 21:50:33 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Benno Lossin <benno.lossin@...ton.me>
Cc: FUJITA Tomonori <fujita.tomonori@...il.com>, netdev@...r.kernel.org,
	rust-for-linux@...r.kernel.org, miguel.ojeda.sandonis@...il.com,
	tmgross@...ch.edu, boqun.feng@...il.com, wedsonaf@...il.com,
	greg@...ah.com
Subject: Re: [PATCH net-next v5 1/5] rust: core abstractions for network PHY
 drivers

> I will try to explain things a bit more.
> 
> So this case is a bit difficult to figure out, because what is
> going on is not really a pattern that is used in Rust.

It is however a reasonably common pattern in the kernel. It stems from
driver writers often don't understand locking. So the core does the
locking, leaving the driver writers to just handle the problems of the
hardware.

Rust maybe makes locking more of a visible issue, but if driver
writers don't understand locking, the language itself does not make
much difference.

> We already have exclusive access to the `phy_device`, so in Rust
> you would not need to lock anything to also have exclusive access to the
> embedded `mii_bus`.

I would actually say its not the PHY drivers problem at all. The
mii_bus is a property of the MDIO layers, and it is the MDIO layers
problem to impose whatever locking it needs for its properties.

Also, mii_bus is not embedded. Its a pointer to an mii_bus. The phy
lock protects the pointer. But its the MDIO layer which needs to
protect what the pointer points to.

	Andrew