On Thu, Oct 5, 2023 at 10:39 PM Wilczynski, Michal <michal.wilczynski@xxxxxxxxx> wrote: > > > > 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 :-) So I went ahead and queued up my versions of patches [1-2/9]. They are present in the acpi-bus branch in linux-pm.git (based on 6.6-rc4) and in the bleeding-edge branch (I'll merge acpi-bus into linux-next next week if all goes well).
