From: "Wilczynski, Michal" <michal.wilczynski@intel.com>
To: "Rafael J. Wysocki" <rafael@kernel.org>
Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>,
<linux-acpi@vger.kernel.org>, <linux-kernel@vger.kernel.org>,
<nvdimm@lists.linux.dev>, <rafael.j.wysocki@intel.com>,
<andriy.shevchenko@intel.com>, <lenb@kernel.org>,
<dan.j.williams@intel.com>, <vishal.l.verma@intel.com>,
<ira.weiny@intel.com>, <rui.zhang@intel.com>,
Elena Reshetova <elena.reshetova@intel.com>
Subject: Re: [PATCH v1 2/9] docs: firmware-guide: ACPI: Clarify ACPI bus concepts
Date: Fri, 6 Oct 2023 19:29:06 +0200 [thread overview]
Message-ID: <065980bb-5890-48ba-b75b-86b3632fd826@intel.com> (raw)
In-Reply-To: <CAJZ5v0h3ZggWKAuKDbFnPbhWpcwnDVk+OrBPRsahM87_H=ob1A@mail.gmail.com>
On 10/6/2023 5:36 PM, Rafael J. Wysocki wrote:
> On Thu, Oct 5, 2023 at 10:39 PM Wilczynski, Michal
> <michal.wilczynski@intel.com> 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@intel.com>
>>>>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
>>>>> ---
>>>>> 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@intel.com>
>>>> 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@intel.com>
>>>> Co-developed-by: Michal Wilczynski <michal.wilczynski@intel.com>
>>>> Signed-off-by: Michal Wilczynski <michal.wilczynski@intel.com>
>>>> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>>>> ---
>>>> 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).
Thanks, great !
Will re-send the rest of the patchset.
Michał
>
next prev parent reply other threads:[~2023-10-06 17:29 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-25 14:48 [PATCH v1 0/9] Replace acpi_driver with platform_driver Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 1/9] ACPI: bus: Make notify wrappers more generic Michal Wilczynski
2023-10-04 19:09 ` Rafael J. Wysocki
2023-10-05 8:09 ` Wilczynski, Michal
2023-10-05 10:57 ` Rafael J. Wysocki
2023-10-05 12:05 ` Wilczynski, Michal
2023-10-05 15:30 ` Rafael J. Wysocki
2023-10-05 17:03 ` Rafael J. Wysocki
2023-10-05 18:27 ` Wilczynski, Michal
2023-10-05 18:29 ` Rafael J. Wysocki
2023-09-25 14:48 ` [PATCH v1 2/9] docs: firmware-guide: ACPI: Clarify ACPI bus concepts Michal Wilczynski
2023-10-05 17:57 ` Rafael J. Wysocki
2023-10-05 18:28 ` Wilczynski, Michal
2023-10-05 18:58 ` Wilczynski, Michal
2023-10-06 15:36 ` Rafael J. Wysocki
2023-10-06 17:29 ` Wilczynski, Michal [this message]
2023-09-25 14:48 ` [PATCH v1 3/9] ACPI: AC: Remove unnecessary checks Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 4/9] ACPI: AC: Use string_choices API instead of ternary operator Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 5/9] ACPI: AC: Replace acpi_driver with platform_driver Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 6/9] ACPI: AC: Rename ACPI device from device to adev Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 7/9] ACPI: NFIT: Replace acpi_driver with platform_driver Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 8/9] ACPI: NFIT: Remove redundant call to to_acpi_dev() Michal Wilczynski
2023-09-25 14:48 ` [PATCH v1 9/9] ACPI: NFIT: Don't use KBUILD_MODNAME for driver name Michal Wilczynski
2023-09-25 15:47 ` Andy Shevchenko
2023-09-25 16:11 ` Dan Williams
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