linux-kernel - Re: [PATCH v2 2/2] of: base: Avoid console probe delay when fw

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Message-ID: <CAGETcx8axPpXFv9Cc59nWrgW9_fYqZUYmNPUg83CTHTBZDC-ZA@mail.gmail.com>
Date:   Thu, 23 Jun 2022 10:30:16 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
Cc:     sascha hauer <sha@...gutronix.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Daniel Scally <djrscally@...il.com>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Len Brown <lenb@...nel.org>, peng fan <peng.fan@....com>,
        kevin hilman <khilman@...nel.org>,
        ulf hansson <ulf.hansson@...aro.org>,
        len brown <len.brown@...el.com>, pavel machek <pavel@....cz>,
        joerg roedel <joro@...tes.org>, will deacon <will@...nel.org>,
        andrew lunn <andrew@...n.ch>,
        heiner kallweit <hkallweit1@...il.com>,
        russell king <linux@...linux.org.uk>,
        "david s. miller" <davem@...emloft.net>,
        eric dumazet <edumazet@...gle.com>,
        jakub kicinski <kuba@...nel.org>,
        paolo abeni <pabeni@...hat.com>,
        linus walleij <linus.walleij@...aro.org>,
        hideaki yoshifuji <yoshfuji@...ux-ipv6.org>,
        david ahern <dsahern@...nel.org>, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        iommu@...ts.linux-foundation.org, netdev@...r.kernel.org,
        linux-gpio@...r.kernel.org, kernel@...gutronix.de,
        devicetree@...r.kernel.org, linux-acpi@...r.kernel.org
Subject: Re: [PATCH v2 2/2] of: base: Avoid console probe delay when fw_devlink.strict=1

On Thu, Jun 23, 2022 at 9:39 AM Andy Shevchenko
<andriy.shevchenko@...ux.intel.com> wrote:
>
> On Thu, Jun 23, 2022 at 12:04:21PM +0200, sascha hauer wrote:
> > On Thu, Jun 23, 2022 at 01:03:43AM -0700, Saravana Kannan wrote:
>
> ...
>
> > I wonder if it wouldn't be a better approach to just probe all devices
> > and record the device(node) they are waiting on. Then you know that you
> > don't need to probe them again until the device they are waiting for
> > is available.
>
> There may be no device, but resource. And we become again to the something like
> deferred probe ugly hack.
>
> The real solution is to rework device driver model in the kernel that it will
> create a graph of dependencies and then simply follow it. But actually it should
> be more than 1 graph, because there are resources and there are power, clock and
> resets that may be orthogonal to the higher dependencies (like driver X provides
> a resource to driver Y).

We already do this with fw_devlink for DT based systems and we do
effectively just probe the devices in graph order (by deferring any
attempts that happen too early and before it even gets to the driver).
The problem is the knowledge of what's considered an optional vs
mandatory dependency and that's affected by the global state of driver
support in the kernel.

-Saravana