linux-kernel - Re: [PATCH v2 16/17] driver core: Refactor fw

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Message-ID: <CAGETcx-MsNyWWT=s1H6hDK+=QvibBLQrT9rM51y5bkomV_+G6g@mail.gmail.com>
Date:   Fri, 11 Dec 2020 09:51:18 -0800
From:   Saravana Kannan <saravanak@...gle.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Qian Cai <qcai@...hat.com>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Ard Biesheuvel <ardb@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Marc Zyngier <maz@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>,
        Grygorii Strashko <grygorii.strashko@...com>,
        Stephen Rothwell <sfr@...b.auug.org.au>,
        linux-efi <linux-efi@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Android Kernel Team <kernel-team@...roid.com>,
        Linux Next Mailing List <linux-next@...r.kernel.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 16/17] driver core: Refactor fw_devlink feature

On Fri, Dec 11, 2020 at 8:34 AM Robin Murphy <robin.murphy@....com> wrote:
>
> On 2020-12-11 14:11, Qian Cai wrote:
> > On Fri, 2020-11-20 at 18:02 -0800, Saravana Kannan wrote:
> >> The current implementation of fw_devlink is very inefficient because it
> >> tries to get away without creating fwnode links in the name of saving
> >> memory usage. Past attempts to optimize runtime at the cost of memory
> >> usage were blocked with request for data showing that the optimization
> >> made significant improvement for real world scenarios.
> >>
> >> We have those scenarios now. There have been several reports of boot
> >> time increase in the order of seconds in this thread [1]. Several OEMs
> >> and SoC manufacturers have also privately reported significant
> >> (350-400ms) increase in boot time due to all the parsing done by
> >> fw_devlink.
> >>
> >> So this patch uses all the setup done by the previous patches in this
> >> series to refactor fw_devlink to be more efficient. Most of the code has
> >> been moved out of firmware specific (DT mostly) code into driver core.
> >>
> >> This brings the following benefits:
> >> - Instead of parsing the device tree multiple times during bootup,
> >>    fw_devlink parses each fwnode node/property only once and creates
> >>    fwnode links. The rest of the fw_devlink code then just looks at these
> >>    fwnode links to do rest of the work.
> >>
> >> - Makes it much easier to debug probe issue due to fw_devlink in the
> >>    future. fw_devlink=on blocks the probing of devices if they depend on
> >>    a device that hasn't been added yet. With this refactor, it'll be very
> >>    easy to tell what that device is because we now have a reference to
> >>    the fwnode of the device.
> >>
> >> - Much easier to add fw_devlink support to ACPI and other firmware
> >>    types. A refactor to move the common bits from DT specific code to
> >>    driver core was in my TODO list as a prerequisite to adding ACPI
> >>    support to fw_devlink. This series gets that done.
> >>
> >> [1] - https://lore.kernel.org/linux-omap/ea02f57e-871d-cd16-4418-c1da4bbc4696@ti.com/
> >> Signed-off-by: Saravana Kannan <saravanak@...gle.com>
> >> Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> >> Tested-by: Grygorii Strashko <grygorii.strashko@...com>
> >
> > Reverting this commit and its dependency:
> >
> > 2d09e6eb4a6f driver core: Delete pointless parameter in fwnode_operations.add_links
> >
> > from today's linux-next fixed a boot crash on an arm64 Thunder X2 server.
>
> Since the call stack implicates the platform-device-wrangling we do in
> IORT code I took a quick look; AFAICS my guess would be it's blowing up
> trying to walk a zeroed list head since "driver core: Add fwnode_init()"
> missed acpi_alloc_fwnode_static().

Thanks Robin. I'm pretty sure this is the reason. I thought I fixed
all ACPI cases, but clearly I missed this one. I'll send out a patch
for this today. If you think there are any other places I missed
please let me know. I'll try some git grep foo to see if I missed any
other instances of fwnode ops being set.

-Saravana