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As per the kernel device driver model, a pwrctl device is the supplier for the PCI device, but the device link that enforces the supplier-consumer relationship was previously created by the pwrctl driver. Therefore, the driver model didn't prevent probing PCI client drivers before probing the corresponding pwrctl drivers. This may lead to a race condition if the PCI device was already powered on by the bootloader (before the pwrctl driver). If the bootloader did not power on the PCI device, this wouldn't create any problem as the pwrctl driver will be the one powering on the device, so the PCI client driver always gets probed afterward. But if the device was already powered on, then the device will be seen by the PCI core and the PCI client driver may get probed before its pwrctl driver. This creates a race condition as the pwrctl driver may change the device power state while the device is being accessed by the client driver. One such issue was already reported on the Qcom X13s platform with the WLAN device and fixed with a hack in the WCN pwrseq driver bya9aaf1ff88("power: sequencing: request the WLAN enable GPIO as-is"). A cleaner way to fix the above mentioned race condition is to ensure that the pwrctl drivers are always probed before the client drivers. If the PCI device is associated with a pwrctl platform device with a power supply, add a device link between the PCI device and the pwrctl device before device_attach() in pci_bus_add_device(). Note that there is no need to explicitly remove the device link as that will be taken care of by the driver core when the PCI device gets removed. Fixes:4565d2652a("PCI/pwrctl: Add PCI power control core code") Fixes:8fb18619d9("PCI/pwrctl: Create platform devices for child OF nodes of the port node") Link: https://lore.kernel.org/r/20241025-pci-pwrctl-rework-v2-3-568756156cbe@linaro.org Tested-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> Tested-by: Krishna chaitanya chundru <quic_krichai@quicinc.com> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org> [bhelgaas: squash fix from https://lore.kernel.org/r/20241120062459.6371-1-manivannan.sadhasivam@linaro.org for SPARCv9 issue reported by Jonathan Currier <dullfire@yahoo.com>] Signed-off-by: Bjorn Helgaas <bhelgaas@google.com> [kwilczynski: wrap code to 80 columns] Signed-off-by: Krzysztof Wilczyński <kwilczynski@kernel.org> Reviewed-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org> Cc: stable+noautosel@kernel.org # Depends on power supply check
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 reStructuredText 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.