linux-kernel - Re: [PATCH V2 02/11] cxl/mem: Implement Get Event Records command

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Date:   Thu, 1 Dec 2022 13:06:50 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     <ira.weiny@...el.com>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Steven Rostedt <rostedt@...dmis.org>,
        Alison Schofield <alison.schofield@...el.com>,
        "Vishal Verma" <vishal.l.verma@...el.com>,
        Ben Widawsky <bwidawsk@...nel.org>,
        Davidlohr Bueso <dave@...olabs.net>,
        Dave Jiang <dave.jiang@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>
Subject: Re: [PATCH V2 02/11] cxl/mem: Implement Get Event Records command

On Wed, 30 Nov 2022 16:27:10 -0800
ira.weiny@...el.com wrote:

> From: Ira Weiny <ira.weiny@...el.com>
> 
> CXL devices have multiple event logs which can be queried for CXL event
> records.  Devices are required to support the storage of at least one
> event record in each event log type.
> 
> Devices track event log overflow by incrementing a counter and tracking
> the time of the first and last overflow event seen.
> 
> Software queries events via the Get Event Record mailbox command; CXL
> rev 3.0 section 8.2.9.2.2.
> 
> Issue the Get Event Record mailbox command on driver load.  Trace each
> record found with a generic record trace.  Trace any overflow
> conditions.
> 
> The device can return up to 1MB worth of event records per query.
> Allocate a shared large buffer to handle the max number of records based
> on the mailbox payload size.
> 
> This patch traces a raw event record only and leaves the specific event
> record types to subsequent patches.
> 
> Macros are created to use for tracing the common CXL Event header
> fields.
> 
> Cc: Steven Rostedt <rostedt@...dmis.org>
> Signed-off-by: Ira Weiny <ira.weiny@...el.com>

Hi Ira,

Looks good to me.  A few trivial suggestions inline. Either way,

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>


> diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> index 16176b9278b4..70b681027a3d 100644
> --- a/drivers/cxl/core/mbox.c
> +++ b/drivers/cxl/core/mbox.c
> @@ -7,6 +7,9 @@

...

> +
> +static void cxl_mem_free_event_buffer(void *data)
> +{
> +	struct cxl_dev_state *cxlds = data;
> +
> +	kvfree(cxlds->event_buf);

Trivial, but why not just pass in the event_buf?

> +}
> +
> +/*
> + * There is a single buffer for reading event logs from the mailbox.  All logs
> + * share this buffer protected by the cxlds->event_buf_lock.
> + */
> +static struct cxl_get_event_payload *alloc_event_buf(struct cxl_dev_state *cxlds)
> +{
> +	struct cxl_get_event_payload *buf;
> +
> +	dev_dbg(cxlds->dev, "Allocating event buffer size %zu\n",
> +		cxlds->payload_size);
> +
> +	buf = kvmalloc(cxlds->payload_size, GFP_KERNEL);

huh. I assumed there would be a devm_kvmalloc() but apparently not..  Ah well
- whilst it might makes sense to add one, let's not tie that up with this series.

> +	if (buf && devm_add_action_or_reset(cxlds->dev,
> +			cxl_mem_free_event_buffer, cxlds))
> +		return NULL;

Trivial, but I'd go for a more wordy but more conventional pattern of
	if (!buf)
		return NULL;

	if (devm_add_action_or_reset())
		return NULL
	
	return buff;
	
> +	return buf;
> +}
> +

...

> diff --git a/drivers/cxl/cxlmem.h b/drivers/cxl/cxlmem.h
> index cd35f43fedd4..55d57f5a64bc 100644
> --- a/drivers/cxl/cxlmem.h
> +++ b/drivers/cxl/cxlmem.h
> @@ -4,6 +4,7 @@
>  #define __CXL_MEM_H__
>  #include <uapi/linux/cxl_mem.h>
>  #include <linux/cdev.h>
> +#include <linux/uuid.h>
>  #include "cxl.h"
>  
>  /* CXL 2.0 8.2.8.5.1.1 Memory Device Status Register */
> @@ -250,12 +251,16 @@ struct cxl_dev_state {
>  
>  	bool msi_enabled;
>  
> +	struct cxl_get_event_payload *event_buf;
Whilst it is obvious (and document at point of allocation),
I think one of the static checkers still warns that all locks must
have comments.  Probably easier to add one now than wait for the
inevitable warning report.

> +	struct mutex event_buf_lock;
> +
>  	int (*mbox_send)(struct cxl_dev_state *cxlds, struct cxl_mbox_cmd *cmd);
>  };
>