linux-kernel - Re: [PATCH] i2c: lpi2c: cache peripheral clock rate

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Date:   Thu, 9 Mar 2023 14:54:56 +0000
From:   "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>
To:     "alexander.stein@...tq-group.com" <alexander.stein@...tq-group.com>
CC:     "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "linux-imx@....com" <linux-imx@....com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "aisheng.dong@....com" <aisheng.dong@....com>
Subject: Re: [PATCH] i2c: lpi2c: cache peripheral clock rate

Hi!

On Thu, 2023-03-09 at 15:37 +0100, Alexander Stein wrote:
>  From: Alexander Sverdlin <alexander.sverdlin@...mens.com>
> > 
> > One of the reasons to do it is to save some CPU cycles on
> > cpu_freq_get()
> > under mutex. The second reason if the (false-positive) lockdep
> > splat caused
> > by the recursive feature of the "prepare_lock" (one clock instance
> > is I2C
> > peripheral clock and another is pcf85063 RTC as clock provider):
> > 
> > ======================================================
> > WARNING: possible circular locking dependency detected
> > 5.15.71+... #1 Tainted: G           O
> 
> Which kernel is this? Mainline or downstream vendor kernel?

found and tested on downstream vendor kernel.

[...]

> 
> 
> What if the peripheral clock rate changes? I guess a notifier similar
> to 
> 90ad2cbe88c2 ("i2c: imx: use clk notifier for rate changes") should
> be added 
> as well.
> 

Good point! Thank you for the hint!

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com