linux-kernel - Re: [PATCH v3] cxl/events: Use a common struct for DRAM and General Media events

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Date: Mon, 20 May 2024 19:55:17 +0200
From: "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
To: Ira Weiny <ira.weiny@...el.com>, Dan Williams <dan.j.williams@...el.com>
Cc: Davidlohr Bueso <dave@...olabs.net>,
 Jonathan Cameron <jonathan.cameron@...wei.com>,
 Dave Jiang <dave.jiang@...el.com>,
 Alison Schofield <alison.schofield@...el.com>,
 Vishal Verma <vishal.l.verma@...el.com>, linux-cxl@...r.kernel.org,
 linux-kernel@...r.kernel.org,
 "Fabio M. De Francesco" <fabio.m.de.francesco@...ux.intel.com>
Subject:
 Re: [PATCH v3] cxl/events: Use a common struct for DRAM and General Media
 events

On Saturday, May 18, 2024 1:26:21 PM GMT+2 Fabio M. De Francesco wrote:
> cxl_event_common was an unfortunate naming choice and caused confusion with
> the existing Common Event Record. Furthermore, its fields didn't map all
> the common information between DRAM and General Media Events.
> 
> Remove cxl_event_common and introduce cxl_event_media_hdr to record common
> information between DRAM and General Media events.
> 
> cxl_event_media_hdr, which is embedded in both cxl_event_gen_media and
> cxl_event_dram, leverages the commonalities between the two events to
> simplify their respective handling.
> 
> Suggested-by: Dan Williams <dan.j.williams@...el.com>
> Signed-off-by: Fabio M. De Francesco <fabio.m.de.francesco@...ux.intel.com>
> ---
> 
> [...]
> -
>  union cxl_event {
>  	struct cxl_event_generic generic;
>  	struct cxl_event_gen_media gen_media;
>  	struct cxl_event_dram dram;
>  	struct cxl_event_mem_module mem_module;
> -	struct cxl_event_common common;
> +	struct cxl_event_media_hdr media_hdr;
>  } __packed;

Today I was thinking about a comment from Ira. He didn't like the addition of 
an event that is not in the specs.[0] (Notice that the other issues have been 
already addressed). 

I dislike the addition of an artificial event for the very same reasons Ira 
expressed.

This additional event could be easily removed by something simple like the 
following diff.

Fabio

[0] https://lore.kernel.org/linux-cxl/66467b8b47170_8c79294b3@iweiny-mobl.notmuch/

diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
index a08f050cc1ca..05de8836adea 100644
--- a/drivers/cxl/core/mbox.c
+++ b/drivers/cxl/core/mbox.c
@@ -875,7 +875,13 @@ void cxl_event_trace_record(const struct cxl_memdev 
*cxlmd,
                guard(rwsem_read)(&cxl_region_rwsem);
                guard(rwsem_read)(&cxl_dpa_rwsem);
 
-               dpa = le64_to_cpu(evt->media_hdr.phys_addr) & CXL_DPA_MASK;
+               if (event_type == CXL_CPER_EVENT_GEN_MEDIA)
+                       dpa = le64_to_cpu(evt->gen_media.media_hdr.phys_addr)
+                             & CXL_DPA_MASK;
+               else if (event_type == CXL_CPER_EVENT_GEN_MEDIA)
+                       dpa = le64_to_cpu(evt->dram.media_hdr.phys_addr)
+                             & CXL_DPA_MASK;
+
                cxlr = cxl_dpa_to_region(cxlmd, dpa);
                if (cxlr)
                        hpa = cxl_trace_hpa(cxlr, cxlmd, dpa);
diff --git a/include/linux/cxl-event.h b/include/linux/cxl-event.h
index 6562663a036d..f0a5be131e6a 100644
--- a/include/linux/cxl-event.h
+++ b/include/linux/cxl-event.h
@@ -97,7 +97,6 @@ union cxl_event {
        struct cxl_event_gen_media gen_media;
        struct cxl_event_dram dram;
        struct cxl_event_mem_module mem_module;
-       struct cxl_event_media_hdr media_hdr;
 } __packed;
 
 /*