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

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

On Thu, 26 Jan 2023 12:22:14 -0800
Dan Williams <dan.j.williams@intel.com> wrote:

> 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>
> > 
> > ---
> > 
> > Open question: Should we only do this if Linux has control of the
> > error handling?  In theory it should be safe anyway given the
> > specification is clear that the timestamp base should always be the
> > same - so subject to small errors we shouldn't cause any firmware first
> > handling to get confused.
> > 
> >  drivers/cxl/core/mbox.c      | 25 +++++++++++++++++++++++++
> >  drivers/cxl/cxlmem.h         |  7 +++++++
> >  drivers/cxl/pci.c            |  5 +++++
> >  include/uapi/linux/cxl_mem.h |  1 +
> >  4 files changed, 38 insertions(+)
> > 
> > diff --git a/drivers/cxl/core/mbox.c b/drivers/cxl/core/mbox.c
> > index b03fba212799..a7317bb142ed 100644
> > --- a/drivers/cxl/core/mbox.c
> > +++ b/drivers/cxl/core/mbox.c
> > @@ -65,6 +65,7 @@ static struct cxl_mem_command cxl_mem_commands[CXL_MEM_COMMAND_ID_MAX] = {
> >  	CXL_CMD(GET_SCAN_MEDIA_CAPS, 0x10, 0x4, 0),
> >  	CXL_CMD(SCAN_MEDIA, 0x11, 0, 0),
> >  	CXL_CMD(GET_SCAN_MEDIA, 0, CXL_VARIABLE_PAYLOAD, 0),
> > +	CXL_CMD(SET_TIMESTAMP, 8, 0, 0),  
> 
> Is there a use case for userspace to need to send its own view
> of 'timestamp' to the device? I think it's ok if this only a
> kernel-internal thing.

Fair enough. Easier to add the interface later if we need to than to rip
it out.

> 
> >  };
> >  
> >  /*
> > @@ -93,6 +94,7 @@ static u16 cxl_disabled_raw_commands[] = {
> >  	CXL_MBOX_OP_SET_SHUTDOWN_STATE,
> >  	CXL_MBOX_OP_SCAN_MEDIA,
> >  	CXL_MBOX_OP_GET_SCAN_MEDIA,
> > +	CXL_MBOX_OP_SET_TIMESTAMP,  
> 
> The criteria I have in mind for commands that should be added to this
> list are things that need to have a kernel control point (like long
> running background commands), or commands with data integrity
> implications that only the kernel can reasonably manage (like shutdown
> state). While it is odd for userspace to send its own timestamps via
> debug kernel builds that enable raw commands, the side effects of
> allowing this seem benign.

Makes sense I'll drop it from this list.
> 
> >  };
> >  
> >  /*
> > @@ -857,6 +859,29 @@ int cxl_mem_create_range_info(struct cxl_dev_state *cxlds)
> >  }
> >  EXPORT_SYMBOL_NS_GPL(cxl_mem_create_range_info, CXL);
> >  
> > +int cxl_set_timestamp(struct cxl_dev_state *cxlds, u64 ts)
> > +{
> > +	struct cxl_mbox_cmd mbox_cmd;
> > +	struct cxl_mbox_set_timestamp_in pi;
> > +
> > +	/*
> > +	 * Command is optional and functionality should not be affected if
> > +	 * the command is not available.
> > +	 */
> > +	if (!test_bit(CXL_MEM_COMMAND_ID_SET_TIMESTAMP, cxlds->enabled_cmds))
> > +		return 0;
> > +
> > +	pi.timestamp = ts;  
> 
> cpu_to_le64()?

Good point.

Thanks,

Jonathan