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

Michael Walle
2020-12-29T03:36:19Z

> 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>

git bisect show that this commit broke my board in 5.11-rc1:

[ 2.294375] sysfs: cannot create duplicate filename '/devices/virtual/devlink/0000:00:00.1--0000:00:00.1'
[ 2.303999] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 5.11.0-rc1-00016-ga0fb284b267 #267
[ 2.312125] Hardware name: Kontron SMARC-sAL28 (4 Lane) (DT)
[ 2.317804] Call trace:
[ 2.320253] dump_backtrace+0x0/0x1b8
[ 2.323936] show_stack+0x20/0x70
[ 2.327263] dump_stack+0xd8/0x134
[ 2.330677] sysfs_warn_dup+0x6c/0x88
[ 2.334351] sysfs_create_dir_ns+0xe8/0x100
[ 2.338547] kobject_add_internal+0x9c/0x290
[ 2.342833] kobject_add+0xa0/0x108
[ 2.346331] device_add+0xfc/0x798
[ 2.349746] device_link_add+0x454/0x5e0
[ 2.353682] fw_devlink_create_devlink+0xb8/0xc8
[ 2.358316] __fw_devlink_link_to_suppliers+0x84/0x180
[ 2.363474] __fw_devlink_link_to_suppliers+0x134/0x180
[ 2.368718] device_add+0x778/0x798
[ 2.372217] device_register+0x28/0x38
[ 2.375979] __mdiobus_register+0x94/0x340
[ 2.380089] of_mdiobus_register+0xb4/0x380
[ 2.384285] enetc_pf_probe+0x73c/0xb10
[ 2.388132] local_pci_probe+0x48/0xb8
[ 2.391896] pci_device_probe+0x120/0x1c0
[ 2.395920] really_probe+0xec/0x3c0
[ 2.399505] driver_probe_device+0x60/0xc0
[ 2.403614] device_driver_attach+0x7c/0x88
[ 2.407810] __driver_attach+0x60/0xe8
[ 2.411570] bus_for_each_dev+0x7c/0xd0
[ 2.415419] driver_attach+0x2c/0x38
[ 2.419004] bus_add_driver+0x194/0x1f8
[ 2.422851] driver_register+0x6c/0x128
[ 2.426698] __pci_register_driver+0x4c/0x58
[ 2.430983] enetc_pf_driver_init+0x2c/0x38
[ 2.435181] do_one_initcall+0x54/0x2d8
[ 2.439029] kernel_init_freeable+0x1fc/0x268
[ 2.443403] kernel_init+0x1c/0x120
[ 2.446904] ret_from_fork+0x10/0x30
[ 2.450502] kobject_add_internal failed for 0000:00:00.1--0000:00:00.1 with -EEXIST, don't try to register things with the same name in the same directory.

Looks like it will generate that link twice? Let me know if I can help
testing.

See also: https://lavalab.kontron.com/scheduler/job/3894#L831

-michael