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    SubjectRe: [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


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