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

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Date:   Mon, 7 Oct 2019 21:58:41 +0800
From:   Cheng-yi Chiang <cychiang@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Tzung-Bi Shih <tzungbi@...gle.com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        ALSA development <alsa-devel@...a-project.org>,
        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 8:27 PM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 10/7/19 1:03 AM, Tzung-Bi Shih 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)
>
> FWIW, I don't think the "_value" in this function name adds any value,
> unless there is going to be some other read function.
ACK
>
> The API should be documented, and state clearly that the caller must release
> the returned value.
ACK
>
> >> +{
> >> +       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.
> >
> kmemdup() ?
ACK
>
> > 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;
>
> Maybe something like -ENOENT would be more appropriate here.
>
ACK
> >> +}
> >> +EXPORT_SYMBOL(vpd_attribute_read_value);
> >> +
>
> I would suggest to use EXPORT_SYMBOL_GPL().
>
ACK

Hi Guenter,
Thanks for the quick review.
I'll update accordingly in v2.

> >>   /*
> >>    * 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
> >>
> >
>