Re: [PATCH v2] cxl/pci: Set the device timestamp

[Jonathan Cameron <Jonathan.Cameron@Huawei.com>]

On Wed, 22 Feb 2023 09:34:14 -0600
Nabeel M Mohamed <nabeelmd.linux@gmail.com> wrote:

> On Mon, Jan 30, 2023 at 03:13:27PM +0000, Jonathan Cameron wrote:
> > CXL r3.0 section 8.2.9.4.2 "Set Timestamp" recommends that the host sets
> > the timestamp after every Conventional or CXL Reset to ensure accurate
> > timestamps. This should include on initial boot up. The time base that
> > is being set is used by a device for the poison list overflow timestamp
> > and all event timestamps.  Note that the command is optional and if
> > not supported and the device cannot return accurate timestamps it will
> > fill the fields in with an appropriate marker (see the specification
> > description of each timestamp).
> > 
> > Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> >  
> 
> Hi Jonathan,
> 
> Could you please educate me on the reason for not supporting a
> "Get Timestamp" mailbox command at this time?
> 
> A use-case that I can think of for having "Get Timestamp" in the UAPI
> is to enable userspace to better correlate the timestamp in the device
> logs with the wall time by querying the current timestamp on the device.
> This could be useful if there's some inaccuracy or skew in the device
> timestamp.
> 
> Would that be a valid use-case or am I misunderstanding something here?
> 
> I can see why "Set Timestamp" is a kernel-internal command but fail to
> see why "Get Timestamp" cannot be in the UAPI.

Hi Nabeel,

I'd be fine with a patch adding the support, it just didn't solve my
immediate problem so I didn't want to make this patch more complex.

Jonathan

> 
> Please clarify.
> 
> Thanks,
> Nabeel