linux-kernel - Re: [PATCH] firmware: vpd: Add an interface to read VPD value

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Date:   Mon, 7 Oct 2019 16:03:26 +0800
From:   Tzung-Bi Shih <tzungbi@...gle.com>
To:     Cheng-Yi Chiang <cychiang@...omium.org>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ALSA development <alsa-devel@...a-project.org>,
        Guenter Roeck <linux@...ck-us.net>,
        Hung-Te Lin <hungte@...omium.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sean Paul <seanpaul@...omium.org>,
        Mark Brown <broonie@...nel.org>, dgreid@...omium.org,
        Tzung-Bi Shih <tzungbi@...omium.org>
Subject: Re: [PATCH] firmware: vpd: Add an interface to read VPD value

On Mon, Oct 7, 2019 at 3:16 PM Cheng-Yi Chiang <cychiang@...omium.org> wrote:
>
> Add an interface for other driver to query VPD value.
> This will be used for ASoC machine driver to query calibration
> data stored in VPD for smart amplifier speaker resistor
> calibration.
>
> Signed-off-by: Cheng-Yi Chiang <cychiang@...omium.org>
> ---
>  drivers/firmware/google/vpd.c              | 16 ++++++++++++++++
>  include/linux/firmware/google/google_vpd.h | 18 ++++++++++++++++++
>  2 files changed, 34 insertions(+)
>  create mode 100644 include/linux/firmware/google/google_vpd.h
>
> diff --git a/drivers/firmware/google/vpd.c b/drivers/firmware/google/vpd.c
> index db0812263d46..71e9d2da63be 100644
> --- a/drivers/firmware/google/vpd.c
> +++ b/drivers/firmware/google/vpd.c
> @@ -65,6 +65,22 @@ static ssize_t vpd_attrib_read(struct file *filp, struct kobject *kobp,
>                                        info->bin_attr.size);
>  }
>
> +int vpd_attribute_read_value(bool ro, const char *key,
> +                            char **value, u32 value_len)
> +{
> +       struct vpd_attrib_info *info;
> +       struct vpd_section *sec = ro ? &ro_vpd : &rw_vpd;
> +
> +       list_for_each_entry(info, &sec->attribs, list) {
> +               if (strcmp(info->key, key) == 0) {
> +                       *value = kstrndup(info->value, value_len, GFP_KERNEL);

Value is not necessary a NULL-terminated string.
kmalloc(info->bin_attr.size) and memcpy(...) would make the most
sense.

The value_len parameter makes less sense.  It seems the caller knows
the length of the value in advance.
Suggest to change the value_len to report the length of value.  I.e.
*value_len = info->bin_attr.size;

Also please check the return value for memory allocation-like
functions (e.g. kstrndup, kmalloc) so that *value won't be NULL but
the function returned 0.

> +                       return 0;
> +               }
> +       }
> +       return -EINVAL;
> +}
> +EXPORT_SYMBOL(vpd_attribute_read_value);
> +
>  /*
>   * vpd_section_check_key_name()
>   *
> diff --git a/include/linux/firmware/google/google_vpd.h b/include/linux/firmware/google/google_vpd.h
> new file mode 100644
> index 000000000000..6f1160f28af8
> --- /dev/null
> +++ b/include/linux/firmware/google/google_vpd.h
> @@ -0,0 +1,18 @@
> +/* SPDX-License-Identifier: GPL-2.0 */
> +/*
> + * Google VPD interface.
> + *
> + * Copyright 2019 Google Inc.
> + */
> +
> +/* Interface for reading VPD value on Chrome platform. */
> +
> +#ifndef __GOOGLE_VPD_H
> +#define __GOOGLE_VPD_H
> +
> +#include <linux/types.h>
> +
> +int vpd_attribute_read_value(bool ro, const char *key,
> +                            char **value, u32 value_len);
> +
> +#endif  /* __GOOGLE_VPD_H */
> --
> 2.23.0.581.g78d2f28ef7-goog
>