linux-kernel - Re: [PATCH 7/8] cxl/memfeature: Add CXL memory device soft PPR control feature

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Message-ID: <20250307090455.00001767@huawei.com>
Date: Fri, 7 Mar 2025 09:04:55 +0800
From: Jonathan Cameron <Jonathan.Cameron@...wei.com>
To: <shiju.jose@...wei.com>
CC: <linux-cxl@...r.kernel.org>, <dan.j.williams@...el.com>,
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Subject: Re: [PATCH 7/8] cxl/memfeature: Add CXL memory device soft PPR
 control feature

On Thu, 27 Feb 2025 22:38:14 +0000
<shiju.jose@...wei.com> wrote:

> From: Shiju Jose <shiju.jose@...wei.com>
> 
> Post Package Repair (PPR) maintenance operations may be supported by CXL
> devices that implement CXL.mem protocol. A PPR maintenance operation
> requests the CXL device to perform a repair operation on its media.
> For example, a CXL device with DRAM components that support PPR features
> may implement PPR Maintenance operations. DRAM components may support two
> types of PPR, hard PPR (hPPR), for a permanent row repair, and Soft PPR
> (sPPR), for a temporary row repair. Soft PPR is much faster than hPPR,
> but the repair is lost with a power cycle.
> 
> During the execution of a PPR Maintenance operation, a CXL memory device:
> - May or may not retain data
> - May or may not be able to process CXL.mem requests correctly, including
> the ones that target the DPA involved in the repair.
> These CXL Memory Device capabilities are specified by Restriction Flags
> in the sPPR Feature and hPPR Feature.
> 
> Soft PPR maintenance operation may be executed at runtime, if data is
> retained and CXL.mem requests are correctly processed. For CXL devices with
> DRAM components, hPPR maintenance operation may be executed only at boot
> because typically data may not be retained with hPPR maintenance operation.
> 
> When a CXL device identifies error on a memory component, the device
> may inform the host about the need for a PPR maintenance operation by using
> an Event Record, where the Maintenance Needed flag is set. The Event Record
> specifies the DPA that should be repaired. A CXL device may not keep track
> of the requests that have already been sent and the information on which
> DPA should be repaired may be lost upon power cycle.
> The userspace tool requests for maintenance operation if the number of
> corrected error reported on a CXL.mem media exceeds error threshold.
> 
> CXL spec 3.2 section 8.2.10.7.1.2 describes the device's sPPR (soft PPR)
> maintenance operation and section 8.2.10.7.1.3 describes the device's
> hPPR (hard PPR) maintenance operation feature.
> 
> CXL spec 3.2 section 8.2.10.7.2.1 describes the sPPR feature discovery and
> configuration.
> 
> CXL spec 3.2 section 8.2.10.7.2.2 describes the hPPR feature discovery and
> configuration.
> 
> Add support for controlling CXL memory device soft PPR (sPPR) feature.
> Register with EDAC driver, which gets the memory repair attr descriptors
> from the EDAC memory repair driver and exposes sysfs repair control
> attributes for PRR to the userspace. For example CXL PPR control for the
> CXL mem0 device is exposed in /sys/bus/edac/devices/cxl_mem0/mem_repairX/
> 
> Add checks to ensure the memory to be repaired is offline and originates
> from a CXL DRAM or CXL gen_media error record reported in the current boot,
> before requesting a PPR operation on the device.
> 
> Tested with QEMU patch for CXL PPR feature.
> https://lore.kernel.org/all/20240730045722.71482-1-dave@stgolabs.net/
> 
> Reviewed-by: Dave Jiang <dave.jiang@...el.com>
> Signed-off-by: Shiju Jose <shiju.jose@...wei.com>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>