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SubjectRe: [PATCH V10 6/9] cxl/port: Read CDAT table
On Thu, Jun 09, 2022 at 09:27:38AM +0100, Jonathan Cameron wrote:
> On Wed, 8 Jun 2022 14:27:14 -0700
> Ira Weiny <ira.weiny@intel.com> wrote:
>
> > On Mon, Jun 06, 2022 at 11:15:41AM -0700, Ben Widawsky wrote:
> > > On 22-06-04 17:50:46, ira.weiny@intel.com wrote:
> > > > From: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> > > >
> >
>
> [snip]
>
> > >
> > > > +
> > > > + entry = cdat_response_pl + 1;
> > > > + entry_dw = task.rv / sizeof(u32);
> > > > + /* Skip Header */
> > > > + entry_dw -= 1;
> > > > + entry_dw = min(length / 4, entry_dw);
> > > > + memcpy(data, entry, entry_dw * sizeof(u32));
> > > > + length -= entry_dw * sizeof(u32);
> > > > + data += entry_dw;
> > > > + entry_handle = FIELD_GET(CXL_DOE_TABLE_ACCESS_ENTRY_HANDLE, cdat_response_pl[0]);
> > >
> > > [0] looks suspicious...
> >
> > Actually I have to claim ignorance on this one. I've carried this from
> > Jonathan's original patches. I'm not as worried about the [0] as that is just
> > the first dword. But I'm confused as to this entry handle now.
> >
> > Jonathan? Help?
>
> Looks right to me. The entryhandle is a field in the upper 16 bits of the
> first dword defined in Read Entry Response table in the CXL spec and also
> used in the request of the next entry (which is more or less a CDAT structure)
> Two magic values.
> 0 - CDAT header (request only - can't be returned)
> 0xFFFF - No more entries.

Thanks!

>
> As we are reading the whole table, we write 0 to first request and from there
> on use the value returned in the response for the next request until we see
> 0xFFFF and stop.
>
> Note IIRC the meaning of entry handle was clarified in a CXL 2.0 errata as
> was a bit ambiguous in the original spec (we had two QEMU implementations
> briefly and they did different things :)

I see it now! I'm going to add a define for 0xFFFF as well.

Ira

>
> Jonathan
>
>
> >
> > >
> > > > +
> > > > + } while (entry_handle != 0xFFFF);
> > > > +
> > > > + return rc;
> > > > +}
> > > > +
>
>

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