linux-kernel - Re: [PATCH 05/21] can: bcm: Don't initialized an unused hrtimer

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Message-ID: <20241030121533.ioTNvYpX@linutronix.de>
Date: Wed, 30 Oct 2024 13:15:33 +0100
From: Nam Cao <namcao@...utronix.de>
To: Oliver Hartkopp <socketcan@...tkopp.net>
Cc: Anna-Maria Behnsen <anna-maria@...utronix.de>,
	Frederic Weisbecker <frederic@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Andreas Hindborg <a.hindborg@...nel.org>,
	Alice Ryhl <aliceryhl@...gle.com>, Miguel Ojeda <ojeda@...nel.org>,
	Kees Cook <kees@...nel.org>, linux-kernel@...r.kernel.org,
	Jakub Kicinski <kuba@...nel.org>
Subject: Re: [PATCH 05/21] can: bcm: Don't initialized an unused hrtimer

On Wed, Oct 30, 2024 at 11:49:49AM +0100, Oliver Hartkopp wrote:
> On 28.10.24 08:29, Nam Cao wrote:
> > The hrtimer "thrtimer" is not used for TX. But this timer is initialized
> > regardless.
> > 
> > Remove the hrtimer_init() for the unused hrtimer and change bcm_remove_op()
> > to make sure hrtimer_cancel() is not called with the uninitialized hrtimer.
> 
> NAK.
> 
> There are several other occurrences of thrtimer that are not covered by
> RX/TX distinction, where the second timer is canceled.
> 
> This one-time init and cancel of an unused hrtimer costs nearly nothing and
> is not even in any hot path.
> 
> So this incomplete patch only adds complexity and potential error cases in
> some 20 y/o code for nothing.

The "real" motivation is preparing to use hrtimer_setup() instead of
hrtimer_init() [1] and deleting hrtimer_init() [2]. The new function
mandates a callback function, and since the TX thrtimer doesn't have a
callback function, hrtimer_setup() cannot be used.

Your concerns are also valid. So I can drop this patch, and use a dummy
function to make hrtimer_setup() happy, like how it's done for the rt2x00
driver [3]. It will make the driver a bit ugly, but it's obvious that it
won't cause any regression.

Best regards,
Nam

[1] https://lore.kernel.org/lkml/e4ce3a3a28625d54ef93e47bfb02f7ffb741758a.1729865232.git.namcao@linutronix.de/
[2] https://lore.kernel.org/lkml/7bde2762d82d30dab184c7a747e76afc41208da0.1729865740.git.namcao@linutronix.de/
[3] https://lore.kernel.org/lkml/49f2bce487f56eb2a3ff572ea6d7de0a43560c0f.1729865232.git.namcao@linutronix.de/