Message-ID: <fa5d6bdd08104cf1a09c4960a0f9bc46@huawei.com>
Date: Fri, 15 Nov 2024 12:21:16 +0000
From: Shiju Jose <shiju.jose@...wei.com>
To: Borislav Petkov <bp@...en8.de>
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Subject: RE: [PATCH v15 11/15] EDAC: Add memory repair control feature

Hi Boris,

Please find reply inline.
>-----Original Message-----
>From: Borislav Petkov <bp@...en8.de>
>Sent: 14 November 2024 13:33
>To: Shiju Jose <shiju.jose@...wei.com>
>Cc: linux-edac@...r.kernel.org; linux-cxl@...r.kernel.org; linux-
>acpi@...r.kernel.org; linux-mm@...ck.org; linux-kernel@...r.kernel.org;
>tony.luck@...el.com; rafael@...nel.org; lenb@...nel.org;
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>Cameron <jonathan.cameron@...wei.com>; gregkh@...uxfoundation.org;
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><tanxiaofei@...wei.com>; Zengtao (B) <prime.zeng@...ilicon.com>; Roberto
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>wanghuiqiang <wanghuiqiang@...wei.com>; Linuxarm
><linuxarm@...wei.com>
>Subject: Re: [PATCH v15 11/15] EDAC: Add memory repair control feature
>
>On Mon, Nov 11, 2024 at 04:54:48PM +0000, Shiju Jose wrote:
>> Presently, 0 (soft memory repair) and 1 (hard memory repair),  depends
>> on which mode/s a memory device is supported.
>
>What if the device supports more than one mode?
>
>> However for CXL memory sparing feature, the persistent mode is
>> configurable at runtime for a memory sparing instance, thus both soft and
>hard sparing are supported.
>> Example given for CXL memory sparing feature in
>> Documentation/edac/memory_repair.rst,
>> root@...alhost:~# cat
>> /sys/bus/edac/devices/cxl_mem0/mem_repair1/persist_mode_avail
>> 0,1
>
>Ok, and how is the user supposed to know what those mean?

Print in  string format?, may be as 'persist'/'volatile'? 

>
>> Kernel sysfs doc mentioned about array of values as follows, though not seen
>much examples.
>> https://docs.kernel.org/filesystems/sysfs.html
>> "Attributes should be ASCII text files, preferably with only one value
>> per file. It is noted that it may not be efficient to contain only one
>> value per file, so it is socially acceptable to express an array of values of the
>same type."
>
>True story. Ok, so there's an exception to that rule.
>
>> The values of these attributes are specific to device and portion of the memory
>to repair.
>> For example, In CXL repair features,
>> CXL memory device identifies a failure on a memory component, device
>> provides the corresponding values of the attributes (DPA, channel,
>> rank, nibble mask, bank group, bank, row, column or sub-channel etc) in an
>event record to the host and to the userspace in the corresponding trace event.
>> Userspace shall use these values for the query resource availability and repair
>operations.
>
>I don't think you're answering my question. Lemme try again:
>
>I am on a machine with such an interface. I do
>
>echo 0xdeadbeef > /sys/devices...
>-EINVAL
>
>echo 0xface > ...
>-EINVAL
>
>How do I know what the allowed ranges are?

I am  fine with adding the support for expose the ranges of these,
but makes more sense to do it when a driver surfaces that can do it. 
I will use the DPA for CXL features as an example of how it would be done and 
it's the one is supported now.

>> This will work for the CXL PPR feature where the result of the query
[...]
>--
>Regards/Gruss,
>    Boris.
>
>https://people.kernel.org/tglx/notes-about-netiquette

Thanks,
Shiju

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