Re: [PATCH v2 16/17] driver core: Refactor fw_devlink feature

Saravana Kannan
2020-12-11T19:31:47Z

On Fri, Dec 11, 2020 at 8:34 AM Robin Murphy <robin.murphy@arm.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@google.com>
> >> Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
> >> Tested-by: Grygorii Strashko <grygorii.strashko@ti.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