On 10/5/2023 8:28 PM, Wilczynski, Michal wrote: > > On 10/5/2023 7:57 PM, Rafael J. Wysocki wrote: >> On Monday, September 25, 2023 4:48:35 PM CEST Michal Wilczynski wrote: >>> Some devices implement ACPI driver as a way to manage devices >>> enumerated by the ACPI. This might be confusing as a preferred way to >>> implement a driver for devices not connected to any bus is a platform >>> driver, as stated in the documentation. Clarify relationships between >>> ACPI device, platform device and ACPI entries. >>> >>> Suggested-by: Elena Reshetova <elena.reshetova@xxxxxxxxx> >>> Signed-off-by: Michal Wilczynski <michal.wilczynski@xxxxxxxxx> >>> --- >>> Documentation/firmware-guide/acpi/enumeration.rst | 13 +++++++++++++ >>> 1 file changed, 13 insertions(+) >>> >>> diff --git a/Documentation/firmware-guide/acpi/enumeration.rst b/Documentation/firmware-guide/acpi/enumeration.rst >>> index 56d9913a3370..f56cc79a9e83 100644 >>> --- a/Documentation/firmware-guide/acpi/enumeration.rst >>> +++ b/Documentation/firmware-guide/acpi/enumeration.rst >>> @@ -64,6 +64,19 @@ If the driver needs to perform more complex initialization like getting and >>> configuring GPIOs it can get its ACPI handle and extract this information >>> from ACPI tables. >>> >>> +ACPI bus >>> +==================== >>> + >>> +Historically some devices not connected to any bus were represented as ACPI >>> +devices, and had to implement ACPI driver. This is not a preferred way for new >>> +drivers. As explained above devices not connected to any bus should implement >>> +platform driver. ACPI device would be created during enumeration nonetheless, >>> +and would be accessible through ACPI_COMPANION() macro, and the ACPI handle would >>> +be accessible through ACPI_HANDLE() macro. ACPI device is meant to describe >>> +information related to ACPI entry e.g. handle of the ACPI entry. Think - >>> +ACPI device interfaces with the FW, and the platform device with the rest of >>> +the system. >>> + >>> DMA support >>> =========== >> I rewrote the above entirely, so here's a new patch to replace this one: >> >> --- >> From: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >> Subject: [PATCH v2 2/9] ACPI: docs: enumeration: Clarify ACPI bus concepts >> >> In some cases, ACPI drivers are implemented as a way to manage devices >> enumerated with the help of the platform firmware through ACPI. >> >> This might be confusing, since the preferred way to implement a driver >> for a device that cannot be enumerated natively, is a platform >> driver, as stated in the documentation. >> >> Clarify relationships between ACPI device objects, platform devices and >> ACPI Namespace entries. >> >> Suggested-by: Elena Reshetova <elena.reshetova@xxxxxxxxx> >> Co-developed-by: Michal Wilczynski <michal.wilczynski@xxxxxxxxx> >> Signed-off-by: Michal Wilczynski <michal.wilczynski@xxxxxxxxx> >> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx> >> --- >> Documentation/firmware-guide/acpi/enumeration.rst | 43 ++++++++++++++++++++++ >> 1 file changed, 43 insertions(+) >> >> Index: linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >> =================================================================== >> --- linux-pm.orig/Documentation/firmware-guide/acpi/enumeration.rst >> +++ linux-pm/Documentation/firmware-guide/acpi/enumeration.rst >> @@ -64,6 +64,49 @@ If the driver needs to perform more comp >> configuring GPIOs it can get its ACPI handle and extract this information >> from ACPI tables. >> >> +ACPI device objects >> +=================== >> + >> +Generally speaking, there are two categories of devices in a system in which >> +ACPI is used as an interface between the platform firmware and the OS: Devices >> +that can be discovered and enumerated natively, through a protocol defined for >> +the specific bus that they are on (for example, configuration space in PCI), >> +without the platform firmware assistance, and devices that need to be described >> +by the platform firmware so that they can be discovered. Still, for any device >> +known to the platform firmware, regardless of which category it falls into, >> +there can be a corresponding ACPI device object in the ACPI Namespace in which >> +case the Linux kernel will create a struct acpi_device object based on it for >> +that device. >> + >> +Those struct acpi_device objects are never used for binding drivers to natively >> +discoverable devices, because they are represented by other types of device >> +objects (for example, struct pci_dev for PCI devices) that are bound to by >> +device drivers (the corresponding struct acpi_device object is then used as >> +an additional source of information on the configuration of the given device). >> +Moreover, the core ACPI device enumeration code creates struct platform_device >> +objects for the majority of devices that are discovered and enumerated with the >> +help of the platform firmware and those platform device objects can be bound to >> +by platform drivers in direct analogy with the natively enumerable devices >> +case. Therefore it is logically inconsistent and so generally invalid to bind >> +drivers to struct acpi_device objects, including drivers for devices that are >> +discovered with the help of the platform firmware. >> + >> +Historically, ACPI drivers that bound directly to struct acpi_device objects >> +were implemented for some devices enumerated with the help of the platform >> +firmware, but this is not recommended for any new drivers. As explained above, >> +platform device objects are created for those devices as a rule (with a few >> +exceptions that are not relevant here) and so platform drivers should be used >> +for handling them, even though the corresponding ACPI device objects are the >> +only source of device configuration information in that case. >> + >> +For every device having a corresponding struct acpi_device object, the pointer >> +to it is returned by the ACPI_COMPANION() macro, so it is always possible to >> +get to the device configuration information stored in the ACPI device object >> +this way. Accordingly, struct acpi_device can be regarded as a part of the >> +interface between the kernel and the ACPI Namespace, whereas device objects of >> +other types (for example, struct pci_dev or struct platform_device) are used >> +for interacting with the rest of the system. >> + >> DMA support >> =========== > Thanks a lot ! > Looks very good, will include this in next revision. > > Michał Aww, forgot that you can also just apply it yourself, so I can just fetch and rebase. Whichever version you prefer is fine with me :-) > >> >> >> >>
