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

[Marc Zyngier]

On 2020-12-11 17:51, Saravana Kannan wrote:
> On Fri, Dec 11, 2020 at 8:34 AM Robin Murphy <robin.murphy@xxxxxxx> 
> 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@xxxxxx/
> > >> Signed-off-by: Saravana Kannan <saravanak@xxxxxxxxxx>
> > >> Tested-by: Laurent Pinchart <laurent.pinchart@xxxxxxxxxxxxxxxx>
> > >> Tested-by: Grygorii Strashko <grygorii.strashko@xxxxxx>
> > >
> > > 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;
 }



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