mirror of
https://github.com/hardkernel/linux.git
synced 2026-06-03 09:41:54 +09:00
301de697d8
This reverts commit3ac8eed625, which did more than it said on the box, and not only it replaced to_phy_driver with phydev->drv, but it also removed the "!drv" check, without actually explaining why that is fine. That patch in fact breaks suspend/resume on any system which has PHY devices with no drivers bound. The stack trace is: Unable to handle kernel NULL pointer dereference at virtual address 00000000000000e8 pc : mdio_bus_phy_suspend+0xd8/0xec lr : dpm_run_callback+0x38/0x90 Call trace: mdio_bus_phy_suspend+0xd8/0xec dpm_run_callback+0x38/0x90 __device_suspend+0x108/0x3cc dpm_suspend+0x140/0x210 dpm_suspend_start+0x7c/0xa0 suspend_devices_and_enter+0x13c/0x540 pm_suspend+0x2a4/0x330 Examples why that assumption is not fine: - There is an MDIO bus with a PHY device that doesn't have a specific PHY driver loaded, because mdiobus_register() automatically creates a PHY device for it but there is no specific PHY driver in the system. Normally under those circumstances, the generic PHY driver will be bound lazily to it (at phy_attach_direct time). But some Ethernet drivers attach to their PHY at .ndo_open time. Until then it, the to-be-driven-by-genphy PHY device will not have a driver. The blamed patch amounts to saying "you need to open all net devices before the system can suspend, to avoid the NULL pointer dereference". - There is any raw MDIO device which has 'plausible' values in the PHY ID registers 2 and 3, which is located on an MDIO bus whose driver does not set bus->phy_mask = ~0 (which prevents auto-scanning of PHY devices). An example could be a MAC's internal MDIO bus with PCS devices on it, for serial links such as SGMII. PHY devices will get created for those PCSes too, due to that MDIO bus auto-scanning, and although those PHY devices are not used, they do not bother anybody either. PCS devices are usually managed in Linux as raw MDIO devices. Nonetheless, they do not have a PHY driver, nor does anybody attempt to connect to them (because they are not a PHY), and therefore this patch breaks that. The goal itself of the patch is questionable, so I am going for a straight revert. to_phy_driver does not seem to have a need to be replaced by phydev->drv, in fact that might even trigger code paths which were not given too deep of a thought. For instance: phy_probe populates phydev->drv at the beginning, but does not clean it up on any error (including EPROBE_DEFER). So if the phydev driver requests probe deferral, phydev->drv will remain populated despite there being no driver bound. If a system suspend starts in between the initial probe deferral request and the subsequent probe retry, we will be calling the phydev->drv->suspend method, but _before_ any phydev->drv->probe call has succeeded. That is to say, if the phydev->drv is allocating any driver-private data structure in ->probe, it pretty much expects that data structure to be available in ->suspend. But it may not. That is a pretty insane environment to present to PHY drivers. In the code structure before the blamed patch, mdio_bus_phy_may_suspend would just say "no, don't suspend" to any PHY device which does not have a driver pointer _in_the_device_structure_ (not the phydev->drv). That would essentially ensure that ->suspend will never get called for a device that has not yet successfully completed probe. This is the code structure the patch is returning to, via the revert. Fixes:3ac8eed625("net: phy: Uniform PHY driver access") Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com> Acked-by: Florian Fainelli <f.fainelli@gmail.com> Link: https://lore.kernel.org/r/20210914140515.2311548-1-vladimir.oltean@nxp.com Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.