linux-kernel - Re: [PATCH v1 12/18] driver core: Add fw_devlink_parse

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Message-ID: <CAGETcx_7b-mUumRTqT7R9zDWANtJnzkPWFyeU1Z6Tw4jK_gdmA@mail.gmail.com>
Date:   Fri, 20 Nov 2020 18:00:11 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Rafael J. Wysocki" <rafael@...nel.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Grygorii Strashko <grygorii.strashko@...com>,
        "Cc: Android Kernel" <kernel-team@...roid.com>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-efi <linux-efi@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v1 12/18] driver core: Add fw_devlink_parse_fwtree()

On Mon, Nov 16, 2020 at 8:25 AM Rafael J. Wysocki <rafael@...nel.org> wrote:
>
> On Thu, Nov 5, 2020 at 12:24 AM Saravana Kannan <saravanak@...gle.com> wrote:
> >
> > This function is a wrapper around fwnode_operations.add_links().
> >
> > This function parses each node in a fwnode tree and create fwnode links
> > for each of those nodes. The information for creating the fwnode links
> > (the supplier and consumer fwnode) is obtained by parsing the properties
> > in each of the fwnodes.
> >
> > This function also ensures that no fwnode is parsed more than once by
> > marking the fwnodes as parsed.
> >
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
> >  drivers/base/core.c    | 19 +++++++++++++++++++
> >  include/linux/fwnode.h |  3 +++
> >  2 files changed, 22 insertions(+)
> >
> > diff --git a/drivers/base/core.c b/drivers/base/core.c
> > index 4a0907574646..ee28d8c7ee85 100644
> > --- a/drivers/base/core.c
> > +++ b/drivers/base/core.c
> > @@ -1543,6 +1543,25 @@ static bool fw_devlink_is_permissive(void)
> >         return fw_devlink_flags == DL_FLAG_SYNC_STATE_ONLY;
> >  }
> >
> > +static void fw_devlink_parse_fwnode(struct fwnode_handle *fwnode)
> > +{
> > +       if (fwnode->flags & FWNODE_FLAG_LINKS_ADDED)
> > +               return;
>
> Why is the flag needed?
>
> Duplicate links won't be created anyway and it doesn't cause the tree
> walk to be terminated.

To avoid parsing a fwnode more than once. The cumulative impact of the
repeated parsing is actually quite high.

And I intentionally didn't do this check at the tree walk level
because DT overlay can add/remove/change individual fwnodes and I want
to reparse those when they are added while avoiding parsing other
nodes that have already been parsed and not changed by DT overlay.

>
> > +
> > +       fwnode_call_int_op(fwnode, add_links, NULL);
> > +       fwnode->flags |= FWNODE_FLAG_LINKS_ADDED;
> > +}
> > +
> > +static void fw_devlink_parse_fwtree(struct fwnode_handle *fwnode)
> > +{
> > +       struct fwnode_handle *child = NULL;
> > +
> > +       fw_devlink_parse_fwnode(fwnode);
> > +
> > +       while ((child = fwnode_get_next_available_child_node(fwnode, child)))
>
> I'd prefer
>
> for (child = NULL; child; child =
> fwnode_get_next_available_child_node(fwnode, child))

I was about to change to this and then realized it won't work. It
would have to be

for (child = fwnode_get_next_available_child_node(fwnode, NULL));
       child;
       child = fwnode_get_next_available_child_node(fwnode, child))

Is that really better? The while() seems a lot more readable to me. I
don't have a strong opinion, so I'll go with whatever you say after
reading this.

>
> > +               fw_devlink_parse_fwtree(child);
> > +}
> > +
> >  static void fw_devlink_link_device(struct device *dev)
> >  {
> >         int fw_ret;
> > diff --git a/include/linux/fwnode.h b/include/linux/fwnode.h
> > index ec02e1e939cc..9aaf9e4f3994 100644
> > --- a/include/linux/fwnode.h
> > +++ b/include/linux/fwnode.h
> > @@ -15,12 +15,15 @@
> >  struct fwnode_operations;
> >  struct device;
> >
>
> Description here, please.

Ack

>
> > +#define FWNODE_FLAG_LINKS_ADDED                BIT(0)
> > +
> >  struct fwnode_handle {
> >         struct fwnode_handle *secondary;
> >         const struct fwnode_operations *ops;
> >         struct device *dev;
> >         struct list_head suppliers;
> >         struct list_head consumers;
> > +       u32 flags;
>
> That's a bit wasteful.  Maybe u8 would suffice for the time being?

Ack.


-Saravana