linux-kernel - Re: [PATCH v2 02/34] component: Introduce the aggregate bus

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Date:   Thu, 7 Oct 2021 18:10:24 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, freedreno@...ts.freedesktop.org,
        Daniel Vetter <daniel.vetter@...ll.ch>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Clark <robdclark@...il.com>,
        Russell King <rmk+kernel@....linux.org.uk>
Subject: Re: [PATCH v2 02/34] component: Introduce the aggregate bus_type

On Thu, Oct 7, 2021 at 1:11 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Stephen Boyd (2021-10-07 11:40:07)
> > Quoting Saravana Kannan (2021-10-06 20:07:11)
> > > On Wed, Oct 6, 2021 at 12:38 PM Stephen Boyd <swboyd@...omium.org> wrote:
> > > > diff --git a/drivers/base/component.c b/drivers/base/component.c
> > > > index 0a41bbe14981..d99e99cabb99 100644
> > > > --- a/drivers/base/component.c
> > > > +++ b/drivers/base/component.c
> > [...]
> > > > +                       continue;
> > > > +
> > > > +               /* Matches put in component_del() */
> > > > +               get_device(&adev->dev);
> > > > +               c->link = device_link_add(&adev->dev, c->dev,
> > > > +                                         DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME);
> > >
> > > Remove the STATELESS flag and you'll get a bunch of other stuff done for free:
> >
> > I tried that and it didn't work for me. The aggregate device never
> > probed and I was left with no display. Let me see if I can reproduce it
> > with logging to provide more details.
>
> This patch fixes it (whitespace damaged sorry).

Not sure why you have to trigger an explicit rescan, but instead of
this patch below, you could also try setting this flag instead?
DL_FLAG_AUTOPROBE_CONSUMER

-Saravana

>
> ----8<----
> diff --git a/drivers/base/component.c b/drivers/base/component.c
> index 65042c9f8a42..43cac9ed70b7 100644
> --- a/drivers/base/component.c
> +++ b/drivers/base/component.c
> @@ -202,7 +202,7 @@ static int find_components(struct aggregate_device *adev)
>                 /* Matches put in component_del() */
>                 get_device(&adev->dev);
>                 c->link = device_link_add(&adev->dev, c->dev,
> -                                         DL_FLAG_STATELESS | DL_FLAG_PM_RUNTIME);
> +                                         DL_FLAG_PM_RUNTIME);
>                 c->adev = adev;
>         }
>
> @@ -749,7 +749,9 @@ static int __component_add(struct device *dev,
> const struct component_ops *ops,
>         mutex_unlock(&component_mutex);
>
>         /* Try to bind */
> -       return bus_rescan_devices(&aggregate_bus_type);
> +       bus_rescan_devices(&aggregate_bus_type);
> +
> +       return 0;
>  }
>
>  /**
>
>
> The important part is ignoring the return value of bus_rescan_devices().
> It's a cycle problem. The last component is probing and calling
> component_add() in its probe function. The call to component_add() is
> trying to probe the aggregate device now that all components are added.
> But when it tries to probe the aggregate device it sees that a supplier,
> which is this component calling compnent_add(), hasn't been probed yet,
> so it returns -EPROBE_DEFER. That is passed up to the component and it
> defers probe.
>
> I don't think the component device cares at all about the aggregate
> device being able to probe or not. We should be able to ignore the
> return value of bus_rescan_devices() in component_add(). I'll add a
> comment to the code here so it's more obvious.