Re: [net-next PATCH v4 09/15] device property: Introduce fwnode_get_id()

From: "Rafael J. Wysocki" <rafael@kernel.org>
To: Calvin Johnson <calvin.johnson@oss.nxp.com>
Cc: Grant Likely <grant.likely@arm.com>,
	"Rafael J . Wysocki" <rafael@kernel.org>,
	Jeremy Linton <jeremy.linton@arm.com>,
	Andrew Lunn <andrew@lunn.ch>,
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	Florian Fainelli <f.fainelli@gmail.com>,
	Russell King - ARM Linux admin <linux@armlinux.org.uk>,
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	Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Subject: Re: [net-next PATCH v4 09/15] device property: Introduce fwnode_get_id()
Date: Fri, 22 Jan 2021 19:35:32 +0100	[thread overview]
Message-ID: <CAJZ5v0hWqfM0tn6N=U2tK_4jOtQSvX5v-XmR7-ti0QfhuF85YQ@mail.gmail.com> (raw)
In-Reply-To: <CAJZ5v0i9XyBKqZS9OL3riAdpmu3St_HZ3JBDcswMbX5pw03gqQ@mail.gmail.com>

On Fri, Jan 22, 2021 at 7:13 PM Rafael J. Wysocki <rafael@kernel.org> wrote:
>
> On Fri, Jan 22, 2021 at 4:46 PM Calvin Johnson
> <calvin.johnson@oss.nxp.com> wrote:
> >
> > Using fwnode_get_id(), get the reg property value for DT node
> > or get the _ADR object value for ACPI node.

This is not accurate AFAICS, because if the "reg" property is present
in the ACPI case, it will be returned then too.

> >
> > Signed-off-by: Calvin Johnson <calvin.johnson@oss.nxp.com>
> > ---
> >
> > Changes in v4:
> > - Improve code structure to handle all cases
> >
> > Changes in v3:
> > - Modified to retrieve reg property value for ACPI as well
> > - Resolved compilation issue with CONFIG_ACPI = n
> > - Added more info into documentation
> >
> > Changes in v2: None
> >
> >  drivers/base/property.c  | 34 ++++++++++++++++++++++++++++++++++
> >  include/linux/property.h |  1 +
> >  2 files changed, 35 insertions(+)
> >
> > diff --git a/drivers/base/property.c b/drivers/base/property.c
> > index 35b95c6ac0c6..f0581bbf7a4b 100644
> > --- a/drivers/base/property.c
> > +++ b/drivers/base/property.c
> > @@ -580,6 +580,40 @@ const char *fwnode_get_name_prefix(const struct fwnode_handle *fwnode)
> >         return fwnode_call_ptr_op(fwnode, get_name_prefix);
> >  }
> >
> > +/**
> > + * fwnode_get_id - Get the id of a fwnode.
> > + * @fwnode: firmware node
> > + * @id: id of the fwnode
> > + *
> > + * This function provides the id of a fwnode which can be either
> > + * DT or ACPI node. For ACPI, "reg" property value, if present will
> > + * be provided or else _ADR value will be provided.
> > + * Returns 0 on success or a negative errno.

What about using the following description instead of the above:

"Retrieve the value of the "reg" property for @fwnode which can be
either DT or ACPI node.  In the ACPI case, if the "reg" property is
missing, evaluate the _ADR object located under the given node, if
present, and provide its return value to the caller.

Return 0 on success or a negative error code.

This function can be used only if it is known valid to treat the _ADR
return value as a fallback replacement for the value of the "reg"
property that is missing in the given use case."

> > + */
> > +int fwnode_get_id(struct fwnode_handle *fwnode, u32 *id)
> > +{
> > +#ifdef CONFIG_ACPI
> > +       unsigned long long adr;
> > +       acpi_status status;
> > +#endif
> > +       int ret;
> > +
> > +       ret = fwnode_property_read_u32(fwnode, "reg", id);
> > +       if (ret) {
> > +#ifdef CONFIG_ACPI
> > +               status = acpi_evaluate_integer(ACPI_HANDLE_FWNODE(fwnode),
> > +                                              METHOD_NAME__ADR, NULL, &adr);
> > +               if (ACPI_FAILURE(status))
> > +                       return -EINVAL;
>
> Please don't return -EINVAL from here, because this means "invalid
> argument" to the caller, but there may be nothing wrong with the
> fwnode and id pointers.
>
> I would return -ENODATA instead.
>
> > +               *id = (u32)adr;
> > +#else
> > +               return ret;
> > +#endif
> > +       }
> > +       return 0;
> > +}
> > +EXPORT_SYMBOL_GPL(fwnode_get_id);
> > +
> >  /**
> >   * fwnode_get_parent - Return parent firwmare node
> >   * @fwnode: Firmware whose parent is retrieved
> > diff --git a/include/linux/property.h b/include/linux/property.h
> > index 0a9001fe7aea..3f41475f010b 100644
> > --- a/include/linux/property.h
> > +++ b/include/linux/property.h
> > @@ -82,6 +82,7 @@ struct fwnode_handle *fwnode_find_reference(const struct fwnode_handle *fwnode,
> >
> >  const char *fwnode_get_name(const struct fwnode_handle *fwnode);
> >  const char *fwnode_get_name_prefix(const struct fwnode_handle *fwnode);
> > +int fwnode_get_id(struct fwnode_handle *fwnode, u32 *id);
> >  struct fwnode_handle *fwnode_get_parent(const struct fwnode_handle *fwnode);
> >  struct fwnode_handle *fwnode_get_next_parent(
> >         struct fwnode_handle *fwnode);
> > --
> > 2.17.1
> >