linux-kernel - [PATCH v2 2/8] EDAC: Update documentation for the CXL memory patrol scrub control feature

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Message-ID: <20250320180450.539-3-shiju.jose@huawei.com>
Date: Thu, 20 Mar 2025 18:04:39 +0000
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Subject: [PATCH v2 2/8] EDAC: Update documentation for the CXL memory patrol scrub control feature

From: Shiju Jose <shiju.jose@...wei.com>

Update the Documentation/edac/scrub.rst to include descriptions and
policies for CXL memory device-based and CXL region-based patrol scrub
control.

Note: This may require inputs from CXL memory experts regarding
region-based scrubbing policies.

Signed-off-by: Shiju Jose <shiju.jose@...wei.com>
---
 Documentation/edac/scrub.rst | 47 ++++++++++++++++++++++++++++++++++++
 1 file changed, 47 insertions(+)

diff --git a/Documentation/edac/scrub.rst b/Documentation/edac/scrub.rst
index daab929cdba1..d1c02bd90090 100644
--- a/Documentation/edac/scrub.rst
+++ b/Documentation/edac/scrub.rst
@@ -264,3 +264,51 @@ Sysfs files are documented in
 `Documentation/ABI/testing/sysfs-edac-scrub`
 
 `Documentation/ABI/testing/sysfs-edac-ecs`
+
+Examples
+--------
+
+The usage takes the form shown in these examples:
+
+1. CXL memory device patrol scrubber
+
+1.1 Device based scrubbing
+
+CXL memory is exposed to memory management subsystem and ultimately userspace
+via CXL devices.
+
+For cases where hardware interleave controls do not directly map to regions of
+Physical Address space, perhaps due to interleave the approach described in 
+1.2 Region based scrubbing section, which is specific to CXL regions should be
+followed. In those cases settings on the presented interface may interact with
+direct control via a device instance specific interface and care must be taken.
+
+Sysfs files for scrubbing are documented in
+`Documentation/ABI/testing/sysfs-edac-scrub`
+
+1.2. Region based scrubbing
+
+CXL memory is exposed to memory management subsystem and ultimately userspace
+via CXL regions. CXL Regions represent mapped memory capacity in system
+physical address space. These can incorporate one or more parts of multiple CXL
+memory devices with traffic interleaved across them. The user may want to control
+the scrub rate via this more abstract region instead of having to figure out the
+constituent devices and program them separately. The scrub rate for each device
+covers the whole device. Thus if multiple regions use parts of that device then
+requests for scrubbing of other regions may result in a higher scrub rate than
+requested for this specific region.
+
+1. When user sets scrub rate for a memory region, the scrub rate for all the CXL
+   memory devices interleaved under that region is updated with the same scrub
+   rate.
+
+2. When user sets scrub rate for a memory device, only the scrub rate for that
+   memory devices is updated though device may be part of a memory region and
+   does not change scrub rate of other memory devices of that memory region.
+
+3. Scrub rate of a CXL memory device may be set via EDAC device or region scrub
+   interface simultaneously. Care must be taken to prevent a race condition, or
+   only region-based setting may be allowed.
+
+Sysfs files for scrubbing are documented in
+`Documentation/ABI/testing/sysfs-edac-scrub`
-- 
2.43.0