linux-kernel - Re: [PATCH v1] of: platform: Batch fwnode parsing in the init

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Date:   Fri, 2 Oct 2020 20:54:23 +0300
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        linux-omap <linux-omap@...r.kernel.org>,
        "open list:THERMAL" <linux-pm@...r.kernel.org>,
        Peter Ujfalusi <peter.ujfalusi@...com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Tony Lindgren <tony@...mide.com>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] of: platform: Batch fwnode parsing in the
 init_machine() path

Hi Saravana,

On Fri, Oct 02, 2020 at 10:51:51AM -0700, Saravana Kannan wrote:
> On Fri, Oct 2, 2020 at 7:08 AM Rob Herring <robh+dt@...nel.org> wrote:
> > On Thu, Oct 1, 2020 at 5:59 PM Saravana Kannan <saravanak@...gle.com> wrote:
> > >
> > > When commit 93d2e4322aa7 ("of: platform: Batch fwnode parsing when
> > > adding all top level devices") optimized the fwnode parsing when all top
> > > level devices are added, it missed out optimizing this for platform
> > > where the top level devices are added through the init_machine() path.
> > >
> > > This commit does the optimization for all paths by simply moving the
> > > fw_devlink_pause/resume() inside of_platform_default_populate().
> > >
> > > Reported-by: Tomi Valkeinen <tomi.valkeinen@...com>
> > > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > > ---
> > >  drivers/of/platform.c | 19 +++++++++++++++----
> > >  1 file changed, 15 insertions(+), 4 deletions(-)
> > >
> > > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > > index 071f04da32c8..79972e49b539 100644
> > > --- a/drivers/of/platform.c
> > > +++ b/drivers/of/platform.c
> > > @@ -501,8 +501,21 @@ int of_platform_default_populate(struct device_node *root,
> > >                                  const struct of_dev_auxdata *lookup,
> > >                                  struct device *parent)
> > >  {
> > > -       return of_platform_populate(root, of_default_bus_match_table, lookup,
> > > -                                   parent);
> > > +       int ret;
> > > +
> > > +       /*
> > > +        * fw_devlink_pause/resume() are only safe to be called around top
> > > +        * level device addition due to locking constraints.
> > > +        */
> > > +       if (!root)
> > > +               fw_devlink_pause();
> > > +
> > > +       ret = of_platform_populate(root, of_default_bus_match_table, lookup,
> > > +                                  parent);
> >
> > of_platform_default_populate() vs. of_platform_populate() is just a
> > different match table. I don't think the behavior should otherwise be
> > different.
> >
> > There's also of_platform_probe() which has slightly different matching
> > behavior. It should not behave differently either with respect to
> > devlinks.
> 
> So I'm trying to do this only when the top level devices are added for
> the first time. of_platform_default_populate() seems to be the most
> common path. For other cases, I think we just need to call
> fw_devlink_pause/resume() wherever the top level devices are added for
> the first time. As I said in the other email, we can't add
> fw_devlink_pause/resume() by default to of_platform_populate().
> 
> Do you have other ideas for achieving "call fw_devlink_pause/resume()
> only when top level devices are added for the first time"?

I'm not an expert in this domain, but before investigating it, would you
be able to share a hack patch that implements this (in the most simple
way) to check if it actually fixes the delays I experience on my system
?

-- 
Regards,

Laurent Pinchart