linux-kernel - Re: [PATCH v1] of: property: fw_devlink: Add support for remote-endpoint

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Date:   Tue, 30 Mar 2021 12:45:52 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Stephen Boyd <swboyd@...omium.org>
Cc:     Frank Rowand <frowand.list@...il.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Rob Herring <robh+dt@...nel.org>,
        Android Kernel Team <kernel-team@...roid.com>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v1] of: property: fw_devlink: Add support for remote-endpoint

On Tue, Mar 30, 2021 at 12:36 PM Stephen Boyd <swboyd@...omium.org> wrote:
>
> Quoting Saravana Kannan (2021-03-30 11:50:55)
> > remote-endpoint property seems to always come in pairs where two devices
> > point to each other. So, we can't really tell from DT if there is a
> > functional probe order dependency between these two devices.
> >
> > However, there can be other dependencies between two devices that point
> > to each other with remote-endpoint. This non-remote-endpoint dependency
> > combined with one of the remote-endpoint dependency can lead to a cyclic
> > dependency[1].
> >
> > To avoid this cyclic dependency from incorrectly blocking probes,
> > fw_devlink needs to be made aware of remote-endpoint dependencies even
> > though remote-endpoint dependencies by themselves won't affect probe
> > ordering (because fw_devlink will see the cyclic dependency between
> > remote-endpoint devices and ignore the dependencies that cause the
> > cycle).
> >
> > Also, if a device ever needs to know if a non-probe-blocking
> > remote-endpoint has finished probing, it can now use the sync_state() to
> > figure it out.
> >
> > [1] - https://lore.kernel.org/lkml/CAGETcx9Snf23wrXqjDhJiTok9M3GcoVYDSyNYSMj9QnSRrA=cA@mail.gmail.com/#t
> > Fixes: ea718c699055 ("Revert "Revert "driver core: Set fw_devlink=on by default""")
> > Reported-by: Stephen Boyd <swboyd@...omium.org>
> > Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> > ---
>
> Tested-by: Stephen Boyd <swboyd@...omium.org>

Thanks!

>
> > diff --git a/drivers/of/property.c b/drivers/of/property.c
> > index 5036a362f52e..2bb3158c9e43 100644
> > --- a/drivers/of/property.c
> > +++ b/drivers/of/property.c
> > @@ -1225,6 +1230,8 @@ static struct device_node *parse_##fname(struct device_node *np,       \
> >   * @parse_prop.prop_name: Name of property holding a phandle value
> >   * @parse_prop.index: For properties holding a list of phandles, this is the
> >   *                   index into the list
> > + * @optional: The property can be an optional dependency.
>
> This bit conflicted for me on linux-next today so I dropped it in favor
> of 3915fed92365 ("of: property: Provide missing member description and
> remove excess param").

Ah looks like a change went into DT git repo but not in driver-core
yet. Yeah, dropping this bit is fine.

Rob/Greg,

I'll leave it to you to deal with the conflict?  I can't send to DT
because the fix needs to land in driver-core because of boot issues
and I can't resolve the conflict in driver-core because the
conflicting change isn't in driver-core yet.

Thanks,
Saravana