Re: [PATCH net] Revert "ravb: Fixed to be able to unload modules"

On 22.09.2020 10:29, Geert Uytterhoeven wrote:

This reverts commit 1838d6c62f57836639bd3d83e7855e0ee4f6defc.

This commit moved the ravb_mdio_init() call (and thus the of_mdiobus_register() call) from the ravb_probe() to the ravb_open() call. This causes a regression during system resume (s2idle/s2ram), as new PHY devices cannot be bound while suspended.

During boot, the Micrel PHY is detected like this:

 Micrel KSZ9031 Gigabit PHY e6800000.ethernet-ffffffff:00: attached PHY driver [Micrel KSZ9031 Gigabit PHY] (mii_bus:phy_addr=e6800000.ethernet-ffffffff:00, irq=228)
 ravb e6800000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off

During system suspend, (A) defer_all_probes is set to true, and (B) usermodehelper_disabled is set to UMH_DISABLED, to avoid drivers being probed while suspended.

A. If CONFIG_MODULES=n, phy_device_register() calling device_add() merely adds the device, but does not probe it yet, as really_probe() returns early due to defer_all_probes being set:

    dpm_resume+0x128/0x4f8
device_resume+0xcc/0x1b0
  dpm_run_callback+0x74/0x340
    ravb_resume+0x190/0x1b8
      ravb_open+0x84/0x770
 of_mdiobus_register+0x1e0/0x468
   of_mdiobus_register_phy+0x1b8/0x250
     of_mdiobus_phy_device_register+0x178/0x1e8
       phy_device_register+0x114/0x1b8
	 device_add+0x3d4/0x798
	   bus_probe_device+0x98/0xa0
	     device_initial_probe+0x10/0x18
	       __device_attach+0xe4/0x140
		 bus_for_each_drv+0x64/0xc8
		   __device_attach_driver+0xb8/0xe0
		     driver_probe_device.part.11+0xc4/0xd8
		       really_probe+0x32c/0x3b8

  Later, phy_attach_direct() notices no PHY driver has been bound,
  and falls back to the Generic PHY, leading to degraded operation:

    Generic PHY e6800000.ethernet-ffffffff:00: attached PHY driver [Generic PHY] (mii_bus:phy_addr=e6800000.ethernet-ffffffff:00, irq=POLL)
    ravb e6800000.ethernet eth0: Link is Up - 1Gbps/Full - flow control off

B. If CONFIG_MODULES=y, request_module() returns early with -EBUSY due to UMH_DISABLED, and MDIO initialization fails completely:

    mdio_bus e6800000.ethernet-ffffffff:00: error -16 loading PHY driver module for ID 0x00221622
    ravb e6800000.ethernet eth0: failed to initialize MDIO
    PM: dpm_run_callback(): ravb_resume+0x0/0x1b8 returns -16
    PM: Device e6800000.ethernet failed to resume: error -16

  Ignoring -EBUSY in phy_request_driver_module(), like was done for
  -ENOENT in commit 21e194425abd65b5 ("net: phy: fix issue with loading
  PHY driver w/o initramfs"), would makes it fall back to the Generic
  PHY, like in the CONFIG_MODULES=n case.

Signed-off-by: Geert Uytterhoeven geert+renesas@glider.be Cc: stable@vger.kernel.org

Reviewed-by: Sergei Shtylyov sergei.shtylyov@gmail.com

---

Commit 1838d6c62f578366 ("ravb: Fixed to be able to unload modules") was already backported to stable v4.4, v4.9, v4.14, v4.19, v5.4, and v5.8), and thus needs to be reverted there, too.

Ugh! Sorry for not noticing the issue with the original patch... :-/

MBR, Sergei