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

[Saravana Kannan <saravanak@google.com>]

On Fri, Dec 11, 2020 at 10:03 AM Marc Zyngier <maz@kernel.org> wrote:
>
> On 2020-12-11 17:51, Saravana Kannan wrote:
> > 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.
>
> Yup, that fixed it here (QDF2400).
>
> Thanks,
>
>          M.
>
> diff --git a/include/linux/acpi.h b/include/linux/acpi.h
> index 39263c6b52e1..2630c2e953f7 100644
> --- a/include/linux/acpi.h
> +++ b/include/linux/acpi.h
> @@ -55,7 +55,7 @@ static inline struct fwnode_handle
> *acpi_alloc_fwnode_static(void)
>         if (!fwnode)
>                 return NULL;
>
> -       fwnode->ops = &acpi_static_fwnode_ops;
> +       fwnode_init(fwnode, &acpi_static_fwnode_ops);
>
>         return fwnode;
>   }
>

Lol, my only contribution to the patch will be the commit text. I'll
send them with reported-by, suggested-by and tested-by if no one less
beats me to it.

-Saravana