netdev - Re: [PATCH net-next v1 2/2] net: phy: qt2025: wait until PHY becomes ready

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Message-Id: <20241003.050722.44816085254739536.fujita.tomonori@gmail.com>
Date: Thu, 03 Oct 2024 05:07:22 +0000 (UTC)
From: FUJITA Tomonori <fujita.tomonori@...il.com>
To: andrew@...n.ch
Cc: fujita.tomonori@...il.com, aliceryhl@...gle.com,
 netdev@...r.kernel.org, rust-for-linux@...r.kernel.org,
 hkallweit1@...il.com, tmgross@...ch.edu, ojeda@...nel.org,
 alex.gaynor@...il.com, gary@...yguo.net, bjorn3_gh@...tonmail.com,
 benno.lossin@...ton.me, a.hindborg@...sung.com
Subject: Re: [PATCH net-next v1 2/2] net: phy: qt2025: wait until PHY
 becomes ready

On Wed, 2 Oct 2024 14:31:07 +0200
Andrew Lunn <andrew@...n.ch> wrote:

> There are some subtleties involved with PHYs, which is why we have our
> own wrapper around the macros in iopoll.h:
> 
> https://elixir.bootlin.com/linux/v6.11.1/source/include/linux/phy.h#L1288
> 
> Normally an IO operation cannot fail. But PHYs are different, a read
> could return -EOPNOTSUPP, -EIO, -ETIMEDOUT etc. That needs to be take
> into account and checked before evaluating the condition.

Thanks, I didn't know this function. I think that a generic
read_poll_timeout in Rust can handle such case.

#define read_poll_timeout(op, val, cond, sleep_us, timeout_us, \
				sleep_before_read, args...) \
({ \
	u64 __timeout_us = (timeout_us); \
	unsigned long __sleep_us = (sleep_us); \
	ktime_t __timeout = ktime_add_us(ktime_get(), __timeout_us); \
	might_sleep_if((__sleep_us) != 0); \
	if (sleep_before_read && __sleep_us) \
		usleep_range((__sleep_us >> 2) + 1, __sleep_us); \
	for (;;) { \
		(val) = op(args); \
		if (cond) \
			break; \

The reason why the C version cannot handle such case is that after
call `op` function, read_poll_timeout macro can't know whether `val`
is an error or not.

In Rust version, 'op' function can return Result type, explicitly
tells success or an error. It can return an error before evaluating
the condition.