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

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Date:   Mon, 7 Oct 2019 16:52:41 +0800
From:   Cheng-yi Chiang <cychiang@...omium.org>
To:     Tzung-Bi Shih <tzungbi@...gle.com>
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>,
        Dylan Reid <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 4:03 PM Tzung-Bi Shih <tzungbi@...gle.com> wrote:
>
> 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.

Thanks for the review.
I will them in v2.

>
> > +                       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
> >