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

Marc Zyngier
2020-12-11T19:39:59Z

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;
}

--
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