linux-kernel - Re: [PATCH v1 7/7] ACPI: property: Allow counting a single value as an array of 1 element

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Date:   Wed, 10 Feb 2021 13:36:00 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Calvin Johnson <calvin.johnson@....nxp.com>
Subject: Re: [PATCH v1 7/7] ACPI: property: Allow counting a single value as
 an array of 1 element

On Wed, Feb 10, 2021 at 12:51 PM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> We allow to read the single value as a first element in the array.
> Unfortunately the counting doesn't work in this case and we can't
> call fwnode_property_count_*() API without getting an error.

It would be good to mention what the symptom of the issue is here.

> Modify acpi_data_prop_read() to always try the single value read
> and thus allow counting the single value as an array of 1 element.
>
> Reported-by: Calvin Johnson <calvin.johnson@....nxp.com>
> Signed-off-by: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>

This is a bug fix, so it should go in before the cleanups in this series IMO.

Also it looks like stable@...r material.

> ---
>  drivers/acpi/property.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/acpi/property.c b/drivers/acpi/property.c
> index 236316ee0e25..d6100585fceb 100644
> --- a/drivers/acpi/property.c
> +++ b/drivers/acpi/property.c
> @@ -913,12 +913,14 @@ static int acpi_data_prop_read(const struct acpi_device_data *data,
>         const union acpi_object *items;
>         int ret;
>
> -       if (val && nval == 1) {
> +       /* Try to read as a single value first */
> +       if (!val || nval == 1) {
>                 ret = acpi_data_prop_read_single(data, propname, proptype, val);

This returns -EINVAL if val is NULL.

>                 if (ret >= 0)
> -                       return ret;
> +                       return val ? ret : 1;

So val cannot be NULL here.

>         }
>
> +       /* It's not the single value, get an array instead */
>         ret = acpi_data_get_property_array(data, propname, ACPI_TYPE_ANY, &obj);
>         if (ret)
>                 return ret;
> --

To me, acpi_fwnode_property_read_string_array() needs to special-case
val == NULL and nval == 0.