linux-kernel - Re: [PATCH] cxl/pci: Change CXL AER support check to use native AER

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Date:   Thu, 2 Nov 2023 14:31:00 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Dan Williams <dan.j.williams@...el.com>,
        Alison Schofield <alison.schofield@...el.com>,
        Terry Bowman <terry.bowman@....com>
CC:     <vishal.l.verma@...el.com>, <ira.weiny@...el.com>,
        <bwidawsk@...nel.org>, <dan.j.williams@...el.com>,
        <dave.jiang@...el.com>, <Jonathan.Cameron@...wei.com>,
        <linux-cxl@...r.kernel.org>,
        <Smita.KoralahalliChannabasappa@....com>, <rrichter@....com>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] cxl/pci: Change CXL AER support check to use native AER

Dan Williams wrote:
> Alison Schofield wrote:
> > On Thu, Nov 02, 2023 at 10:52:32AM -0500, Terry Bowman wrote:
> > > Native CXL protocol errors are delivered to the OS through AER
> > > reporting. The owner of AER owns CXL Protocol error management with
> > > respect to _OSC negotiation.[1] CXL device errors are handled by a
> > > separate interrupt with native control gated by _OSC control field
> > > 'CXL Memory Error Reporting Control'.
> > > 
> > > The CXL driver incorrectly checks for 'CXL Memory Error Reporting
> > > Control' before accessing AER registers and caching RCH downport
> > > AER registers. Replace the current check in these 2 cases with
> > > native AER checks.
> > 
> > Hi Terry,  Does this have a user visible impact? 
> 
> Saw this after I applied it. It is good feedback in general.
> 
> The reason I did not ask for this clarification was that this is fixing
> brand new code and was just using the wrong flag, so I had the context.
> A backporter will never need to make a judgement call about this patch.
> 
> The end user impact is that CXL protocol errors that could be handled by
> AER will not be handled if Linux failed to negotiate memory error
> handling. Memory errors are strictly related to memory-error-record
> events, not protocol errors.

However, to that point the "Fixes:" tag looks wrong, it should be:

f05fd10d138d cxl/pci: Add RCH downstream port AER register discovery