linux-kernel - Re: [PATCH 1/6] of: base: Add function to check for status = "reserved"

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Message-ID: <CAL_Jsq+rKGv39zHTxNx0A7=X4K48nXRLqWonecG5SobdJq3yKw@mail.gmail.com>
Date:   Wed, 29 Sep 2021 10:49:58 -0500
From:   Rob Herring <robh+dt@...nel.org>
To:     Zev Weiss <zev@...ilderbeest.net>
Cc:     OpenBMC Maillist <openbmc@...ts.ozlabs.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeremy Kerr <jk@...econstruct.com.au>,
        Joel Stanley <joel@....id.au>,
        Cédric Le Goater <clg@...d.org>,
        Frank Rowand <frowand.list@...il.com>,
        devicetree@...r.kernel.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/6] of: base: Add function to check for status = "reserved"

On Wed, Sep 29, 2021 at 6:54 AM Zev Weiss <zev@...ilderbeest.net> wrote:
>
> Per v0.3 of the Devicetree Specification [0]:
>
>   Indicates that the device is operational, but should not be used.
>   Typically this is used for devices that are controlled by another
>   software component, such as platform firmware.
>
> One use-case for this is in OpenBMC, where certain devices (such as a
> BIOS flash chip) may be shared by the host and the BMC, but cannot be
> accessed by the BMC during its usual boot-time device probing, because
> they require additional (potentially elaborate) coordination with the
> host to arbitrate which processor is controlling the device.
>
> Devices marked with this status should thus be instantiated, but not
> have a driver bound to them or be otherwise touched.
>
> [0] https://github.com/devicetree-org/devicetree-specification/releases/download/v0.3/devicetree-specification-v0.3.pdf
>
> Signed-off-by: Zev Weiss <zev@...ilderbeest.net>
> ---
>  drivers/of/base.c  | 53 +++++++++++++++++++++++++++++++++++++++-------
>  include/linux/of.h |  6 ++++++
>  2 files changed, 51 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index f720c0d246f2..c5cc178fc6bd 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -579,14 +579,18 @@ int of_machine_is_compatible(const char *compat)
>  EXPORT_SYMBOL(of_machine_is_compatible);
>
>  /**
> - *  __of_device_is_available - check if a device is available for use
> + * __of_device_check_status - check if a device's status matches a particular string
>   *
> - *  @device: Node to check for availability, with locks already held
> + * @device: Node to check status of, with locks already held
> + * @val: Status string to check for
> + * @alt: Optional alternate status string to check for (NULL to check only @val)
> + * @dflt: default to return if status property absent
>   *
> - *  Return: True if the status property is absent or set to "okay" or "ok",
> - *  false otherwise
> + * Return: True if status property exists and matches either @val or @alt.
> + * @dflt if status property is absent.  False otherwise.
>   */
> -static bool __of_device_is_available(const struct device_node *device)
> +static bool __of_device_check_status(const struct device_node *device, const char *val,
> +                                     const char *alt, bool dflt)

How about val==NULL means available/okay and then you can get rid of
alt and dflt.

Otherwise, I'd simply not try to share the implementation here and
just add of_device_is_reserved().

Rob