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

[Nabeel M Mohamed <nabeelmd.linux@gmail.com>]

On Wed, Feb 22, 2023 at 04:27:00PM +0000, Jonathan Cameron wrote:
> 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

Great, thanks for clarifying Jonathan!

I'll be happy to post a patch which adds support for "Get Timestamp".

Btw, this will be my first patch to the CXL driver.
So, I'm wondering if there's any checklist listing the prerequisites
for submitting a patch to the CXL driver - for instance, requirements
on adding new tests for coverage, any existing CXL regression suites
that the patch must pass, etc.

Any pointers on the above would be greatly appreciated!

Thanks,
Nabeel