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

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Date:   Thu, 1 Dec 2022 07:10:59 -0800
From:   Ira Weiny <ira.weiny@...el.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.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 Thu, Dec 01, 2022 at 01:06:50PM +0000, Jonathan Cameron wrote:
> 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?

Just following the pattern that 'cxl_mem_*' functions take a cxlds parameter.
<shrug>

I'm going to leave this because it is tested.

> 
> > +}
> > +
> > +/*
> > + * 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

Nope I've learned my lesson and checked first!

> - whilst it might makes sense to add one, let's not tie that up with this series.

Yep I did not want to hold this up for something like that.

> 
> > +	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

I've been beat up in the past for not combining statements before.  So I've a
bad habit sometimes.

This pattern is a bit more clear.  Since I'm adding the comment below I'll
change it.

> 	
> 	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.

Well 0-day did not complain.  :-/  But I know there are other checkers out
there; better to add now, thanks.

Thanks for the review,
Ira

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