linux-kernel - [PATCH v1 2/9] docs: firmware-guide: ACPI: Clarify ACPI bus concepts

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Message-ID: <20230925144842.586829-3-michal.wilczynski@intel.com>
Date:   Mon, 25 Sep 2023 17:48:35 +0300
From:   Michal Wilczynski <michal.wilczynski@...el.com>
To:     linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
        nvdimm@...ts.linux.dev
Cc:     rafael.j.wysocki@...el.com, andriy.shevchenko@...el.com,
        lenb@...nel.org, dan.j.williams@...el.com,
        vishal.l.verma@...el.com, ira.weiny@...el.com, rui.zhang@...el.com,
        Michal Wilczynski <michal.wilczynski@...el.com>,
        Elena Reshetova <elena.reshetova@...el.com>
Subject: [PATCH v1 2/9] docs: firmware-guide: ACPI: Clarify ACPI bus concepts

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@...el.com>
Signed-off-by: Michal Wilczynski <michal.wilczynski@...el.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
 ===========
 
-- 
2.41.0