linux-kernel - Re: [PATCH v3] i2c: lpi2c: cache peripheral clock rate

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Date:   Mon, 15 May 2023 13:11:33 +0000
From:   "Sverdlin, Alexander" <alexander.sverdlin@...mens.com>
To:     "alexander.stein@...tq-group.com" <alexander.stein@...tq-group.com>,
        "linux-imx@....com" <linux-imx@....com>
CC:     "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "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 v3] i2c: lpi2c: cache peripheral clock rate

Hello Alexander,

On Fri, 2023-04-21 at 15:48 +0200, Alexander Stein wrote:
> > +       lpi2c_imx->clk_change_nb.notifier_call =
> > lpi2c_imx_clk_change_cb;
> > +       ret = devm_clk_notifier_register(&pdev->dev, lpi2c_imx-
> > >clks[0].clk,
> > +                                        &lpi2c_imx-
> > >clk_change_nb);
> > +       if (ret)
> > +               return dev_err_probe(&pdev->dev, ret,
> > +                                    "can't register peripheral
> > clock 
> notifier\n");
> > +       lpi2c_imx->rate_per = clk_get_rate(lpi2c_imx->clks[0].clk);
> > +       if (!lpi2c_imx->rate_per) {
> > +               dev_err(&pdev->dev, "can't get I2C peripheral clock
> rate\n");
> > +               return -EINVAL;
> > +       }
> > +
> 
> I would switch the order of the calls to devm_clk_notifier_register()
> and 
> clk_get_rate(). AFAICS this looks like a possible lost update. The
> notifier 
> might change rate_per before the (old) value from clk_get_rate is
> actually 
> assigned.

just swapping would not be enough I believe, in the case update event
happens between clk_get_rate() and devm_clk_notifier_register(). I'll
think about it...

-- 
Alexander Sverdlin
Siemens AG
www.siemens.com