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Date:   Tue, 29 Dec 2020 04:34:40 +0100
From:   Michael Walle <michael@...le.cc>
To:     saravanak@...gle.com
Cc:     ardb@...nel.org, devicetree@...r.kernel.org,
        frowand.list@...il.com, gregkh@...uxfoundation.org,
        grygorii.strashko@...com, kernel-team@...roid.com,
        laurent.pinchart@...asonboard.com, lenb@...nel.org,
        linux-acpi@...r.kernel.org, linux-efi@...r.kernel.org,
        linux-kernel@...r.kernel.org, maz@...nel.org, rafael@...nel.org,
        rjw@...ysocki.net, robh+dt@...nel.org, tglx@...utronix.de,
        tomi.valkeinen@...com, Michael Walle <michael@...le.cc>
Subject: Re: [PATCH v2 16/17] driver core: Refactor fw_devlink feature

> 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@...gle.com>
> Tested-by: Laurent Pinchart <laurent.pinchart@...asonboard.com>
> Tested-by: Grygorii Strashko <grygorii.strashko@...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

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