linux-kernel - Re: [PATCH 1/2] ASoC: Intel: maxim-common: get codec number from ACPI

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Date:   Mon, 24 Jul 2023 14:16:22 +0300
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     "Lu, Brent" <brent.lu@...el.com>
Cc:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "Rojewski, Cezary" <cezary.rojewski@...el.com>,
        Liam Girdwood <liam.r.girdwood@...ux.intel.com>,
        Peter Ujfalusi <peter.ujfalusi@...ux.intel.com>,
        Bard Liao <yung-chuan.liao@...ux.intel.com>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Kai Vehmanen <kai.vehmanen@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Zhi, Yong" <yong.zhi@...el.com>,
        Ajye Huang <ajye_huang@...pal.corp-partner.google.com>,
        "Bhat, Uday M" <uday.m.bhat@...el.com>,
        Terry Cheong <htcheong@...omium.org>,
        "Chiang, Mac" <mac.chiang@...el.com>,
        "R, Dharageswari" <dharageswari.r@...el.com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>
Subject: Re: [PATCH 1/2] ASoC: Intel: maxim-common: get codec number from ACPI

On Mon, Jul 24, 2023 at 11:06:02AM +0000, Lu, Brent wrote:
> > > > +/* helper function to get the number of specific codec */
> > 
> > ...and leak a lot of reference counts...
> > 
> > > > +static int get_num_codecs(const char *hid) {
> > > > +	struct acpi_device *adev = NULL;
> > > > +	int dev_num = 0;
> > > > +
> > > > +	do {
> > > > +		adev = acpi_dev_get_next_match_dev(adev, hid, NULL, -1);
> > >
> > > Humm, I am a bit worried about reference counts.
> > >
> > > See
> > > https://elixir.bootlin.com/linux/latest/source/drivers/acpi/utils.c#L9
> > > 16, it's not clear to me where the get() is done.
> > >
> > > Adding Andy to make sure this is done right.
> > 
> > Thank you for Cc'ing.
> > 
> > Yes, the above code is problematic. One has to use the respective for_each macro
> > (defined nearby the used API).
> > 
> > > > +		if (adev)
> > > > +			dev_num++;
> > > > +	} while (adev != NULL);
> > > > +
> > > > +	return dev_num;
> > > > +}

> Each invocation of acpi_dev_get_next_match_dev() calls acpi_dev_put() to release the
> adev from previous call. And the last call returns NULL. It seems to me the reference count
> should be fine. Is my understanding correct?

Ah, right. sorry for the confusion. That's why we have a macro
to not think about these details :-)

> I saw the macro for_each_acpi_dev_match and re-write the function as follow. Thanks for
> suggesting using the macro.
> 
> /* helper function to get the number of specific codec */
> static int get_num_codecs(const char *hid) {
> 	struct acpi_device *adev;

> 	int dev_num = 0;

size_t here or at least unsigned int is more correct.

> 	for_each_acpi_dev_match(adev, hid, NULL, -1)
> 		dev_num++;
> 
> 	return dev_num;
> }

Otherwise, yes, that's what I have in mind.

> Will test it in next few days.

-- 
With Best Regards,
Andy Shevchenko