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

Ira Weiny
2022-12-01T15:13:39Z

On Thu, Dec 01, 2022 at 01:06:50PM +0000, Jonathan Cameron wrote:
> On Wed, 30 Nov 2022 16:27:10 -0800
> ira.weiny@intel.com wrote:
>
> > From: Ira Weiny <ira.weiny@intel.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@goodmis.org>
> > Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> Hi Ira,
>
> Looks good to me. A few trivial suggestions inline. Either way,
>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.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);
> > };
> >
>
>