Le Tue, 22 Feb 2022 10:24:13 +0100, Andy Shevchenko <andy.shevchenko@xxxxxxxxx> a écrit : > > > If you want to use the device on an ACPI based platform, you need to > > > describe it in ACPI as much as possible. The rest we may discuss. > > > > Agreed but the PCIe card might also be plugged in a system using a > > device-tree description (ARM for instance). I should I do that without > > duplicating the description both in DT and ACPI ? > > Why is it (duplication) a problem? > Each platform has its own kind of description, so one needs to provide > it in the format the platform accepts. > The problem that I see is not only duplication but also that the PCIe card won't work out of the box and will need a specific SSDT overlays each time it is used. According to your document about SSDT overlays, there is no way to load this from the driver. This means that the user will have to compile a platform specific .aml file to match its platform configuration. If the user wants to change the PCIe port, than I guess it will have to load another .aml file. I do not think a user expect to do so when plugging a PCIe card. Moreover, the APCI documentation [1] says the following: "PCI devices, which are below the host bridge, generally do not need to be described via ACPI. The OS can discover them via the standard PCI enumeration mechanism, using config accesses to discover and identify devices and read and size their BARs. However, ACPI may describe PCI devices if it provides power management or hotplug functionality for them or if the device has INTx interrupts connected by platform interrupt controllers and a _PRT is needed to describe those connections." The device I want to use (a PCIe switch) does not fall into these categories so there should be no need to describe it using ACPI. Regarding the use of software nodes, the documentation also says that: "The software nodes can be used to complement fwnodes representing real firmware nodes when they are incomplete, for example missing device properties, *and to supply the primary fwnode when the firmware lacks hardware description for a device completely.*" I think my device falls into this last category but I might be wrong. I understand that using software_node is probably not the best idea to do so but I did not found any other convenient way to do it and SSDT overlays do not really seems to be ideal. I would be glad if you could provide me with an example of such usage to check if it's really usable. Thanks, [1] https://www.kernel.org/doc/html/latest/PCI/acpi-info.html -- Clément Léger, Embedded Linux and Kernel engineer at Bootlin https://bootlin.com
