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

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Date:   Fri, 2 Apr 2021 17:07:24 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Stephen Boyd <swboyd@...omium.org>, kernel-team@...roid.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1] of: property: fw_devlink: Add support for
 remote-endpoint

On Tue, Mar 30, 2021 at 11:50:55AM -0700, Saravana Kannan wrote:
> 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>
> ---
> Rob/Greg,
> 
> This needs to go into driver-core due to the Fixes.

Now picked up, thanks.

greg k-h