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From:   Jon Hunter <jonathanh@nvidia.com>
Subject: Re: [PATCH v1 0/5] Enable fw_devlink=on by default
To:     Saravana Kannan <saravanak@google.com>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>
CC:     <kernel-team@android.com>, <linux-kernel@vger.kernel.org>,
        Jisheng Zhang <Jisheng.Zhang@synaptics.com>,
        Kevin Hilman <khilman@baylibre.com>,
        John Stultz <john.stultz@linaro.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,
        Marc Zyngier <maz@kernel.org>,
        linux-tegra <linux-tegra@vger.kernel.org>
References: <20201218031703.3053753-1-saravanak@google.com>
Message-ID: <56f7d032-ba5a-a8c7-23de-2969d98c527e@nvidia.com>
Date:   Wed, 13 Jan 2021 11:30:16 +0000
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On 18/12/2020 03:16, Saravana Kannan wrote:
> As discussed in LPC 2020, cyclic dependencies in firmware that couldn't
> be broken using logic was one of the last remaining reasons
> fw_devlink=on couldn't be set by default.
> 
> This series changes fw_devlink so that when a cyclic dependency is found
> in firmware, the links between those devices fallback to permissive mode
> behavior. This way, the rest of the system still benefits from
> fw_devlink, but the ambiguous cases fallback to permissive mode.
> 
> Setting fw_devlink=on by default brings a bunch of benefits (currently,
> only for systems with device tree firmware):
> * Significantly cuts down deferred probes.
> * Device probe is effectively attempted in graph order.
> * Makes it much easier to load drivers as modules without having to
>   worry about functional dependencies between modules (depmod is still
>   needed for symbol dependencies).


One issue we have come across with this is the of_mdio.c driver. On
Tegra194 Jetson Xavier I am seeing the following ...

boot: logs: [       4.194791] WARNING KERN WARNING: CPU: 0 PID: 1 at /dvs/git/dirty/git-master_l4t-upstream/kernel/drivers/base/core.c:1189 device_links_driver_bound+0x240/0x260
boot: logs: [       4.207683] WARNING KERN Modules linked in:
boot: logs: [       4.210691] WARNING KERN CPU: 0 PID: 1 Comm: swapper/0 Not tainted 5.11.0-rc3-next-20210112-gdf869cab4b35 #1
boot: logs: [       4.219221] WARNING KERN Hardware name: NVIDIA Jetson AGX Xavier Developer Kit (DT)
boot: logs: [       4.225628] WARNING KERN pstate: 80400009 (Nzcv daif +PAN -UAO -TCO BTYPE=--)
boot: logs: [       4.231542] WARNING KERN pc : device_links_driver_bound+0x240/0x260
boot: logs: [       4.236587] WARNING KERN lr : device_links_driver_bound+0xf8/0x260
boot: logs: [       4.241560] WARNING KERN sp : ffff800011f4b980
boot: logs: [       4.244819] WARNING KERN x29: ffff800011f4b980 x28: ffff00008208a0a0
boot: logs: [       4.250051] WARNING KERN x27: ffff00008208a080 x26: 00000000ffffffff
boot: logs: [       4.255271] WARNING KERN x25: 0000000000000003 x24: ffff800011b99000
boot: logs: [       4.260489] WARNING KERN x23: 0000000000000001 x22: ffff800011df14f0
boot: logs: [       4.265706] WARNING KERN x21: ffff800011f4b9f8 x20: ffff800011df1000
boot: logs: [       4.270934] WARNING KERN x19: ffff00008208a000 x18: 0000000000000005
boot: logs: [       4.276166] WARNING KERN x17: 0000000000000007 x16: 0000000000000001
boot: logs: [       4.281382] WARNING KERN x15: ffff000080030c90 x14: ffff0000805c9df8
boot: logs: [       4.286618] WARNING KERN x13: 0000000000000000 x12: ffff000080030c90
boot: logs: [       4.291847] WARNING KERN x11: ffff0000805c9da8 x10: 0000000000000040
boot: logs: [       4.297061] WARNING KERN x9 : ffff000080030c98 x8 : 0000000000000000
boot: logs: [       4.302291] WARNING KERN x7 : 0000000000000009 x6 : 0000000000000000
boot: logs: [       4.307509] WARNING KERN x5 : ffff000080100000 x4 : 0000000000000000
boot: logs: [       4.312739] WARNING KERN x3 : ffff800011df1e38 x2 : ffff000080908c10
boot: logs: [       4.317956] WARNING KERN x1 : 0000000000000001 x0 : ffff0000809ca400
boot: logs: [       4.323183] WARNING KERN Call trace:
boot: logs: [       4.325593] WARNING KERN  device_links_driver_bound+0x240/0x260
boot: logs: [       4.330301] WARNING KERN  driver_bound+0x70/0xd0
boot: logs: [       4.333740] WARNING KERN  device_bind_driver+0x50/0x60
boot: logs: [       4.337671] WARNING KERN  phy_attach_direct+0x258/0x2e0
boot: logs: [       4.341718] WARNING KERN  phylink_of_phy_connect+0x7c/0x140
boot: logs: [       4.346081] WARNING KERN  stmmac_open+0xb04/0xc70
boot: logs: [       4.349612] WARNING KERN  __dev_open+0xe0/0x190
boot: logs: [       4.352972] WARNING KERN  __dev_change_flags+0x16c/0x1b8
boot: logs: [       4.357081] WARNING KERN  dev_change_flags+0x20/0x60
boot: logs: [       4.360856] WARNING KERN  ip_auto_config+0x2a0/0xfe8
boot: logs: [       4.364633] WARNING KERN  do_one_initcall+0x58/0x1b8
boot: logs: [       4.368405] WARNING KERN  kernel_init_freeable+0x1ec/0x240
boot: logs: [       4.372698] WARNING KERN  kernel_init+0x10/0x110
boot: logs: [       4.376130] WARNING KERN  ret_from_fork+0x10/0x18


So looking at this change does this mean that the of_mdio needs to be
converted to a proper driver? I would have thought that this will be
seen on several platforms.

Cheers
Jon

-- 
nvpublic