On Thu, 23 Jun 2022 21:19:43 -0700
Dan Williams <dan.j.williams@xxxxxxxxx> wrote:
> The ACPI CXL Fixed Memory Window Structure (CFMWS) defines multiple
> methods to determine which host bridge provides access to a given
> endpoint relative to that device's position in the interleave. The
> "Interleave Arithmetic" defines either a "standard modulo" /
> round-random algorithm, or "xormap" based algorithm which can be defined
> as a non-linear transform. Given that there are already more options
> beyond "standard modulo" and that "xormap" may turn out to be ACPI CXL
> specific, provide a callback for the region provisioning code to map
> endpoint positions back to expected host bridge id (cxl_dport target).
>
> For now just support the simple modulo math case and save the xormap for
> a follow-on change.
>
> Signed-off-by: Dan Williams <dan.j.williams@xxxxxxxxx>
Reviewed-by: Jonathan Cameron <Jonathan.Cameron@xxxxxxxxxx>
> ---
> drivers/cxl/core/port.c | 15 +++++++++++++++
> drivers/cxl/cxl.h | 2 ++
> 2 files changed, 17 insertions(+)
>
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index 562a6453249b..7756409d0a58 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -1422,6 +1422,20 @@ static int decoder_populate_targets(struct cxl_switch_decoder *cxlsd,
> return rc;
> }
>
> +static struct cxl_dport *cxl_hb_modulo(struct cxl_root_decoder *cxlrd, int pos)
> +{
> + struct cxl_switch_decoder *cxlsd = &cxlrd->cxlsd;
> + struct cxl_decoder *cxld = &cxlsd->cxld;
> + int iw;
> +
> + iw = cxld->interleave_ways;
> + if (dev_WARN_ONCE(&cxld->dev, iw != cxlsd->nr_targets,
> + "misconfigured root decoder\n"))
> + return NULL;
> +
> + return cxlrd->cxlsd.target[pos % iw];
> +}
> +
> static struct lock_class_key cxl_decoder_key;
>
> /**
> @@ -1466,6 +1480,7 @@ static struct cxl_decoder *cxl_decoder_alloc(struct cxl_port *port,
> if (rc < 0)
> goto err;
> atomic_set(&cxlrd->region_id, rc);
> + cxlrd->calc_hb = cxl_hb_modulo;
> } else
> cxlsd = NULL;
> } else {
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 9340deccad4f..30227348f768 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -315,11 +315,13 @@ struct cxl_switch_decoder {
> * struct cxl_root_decoder - Static platform CXL address decoder
> * @res: host / parent resource for region allocations
> * @region_id: region id for next region provisioning event
> + * @calc_hb: which host bridge covers the n'th position by granularity
> * @cxlsd: base cxl switch decoder
> */
> struct cxl_root_decoder {
> struct resource *res;
> atomic_t region_id;
> + struct cxl_dport *(*calc_hb)(struct cxl_root_decoder *cxlrd, int pos);
> struct cxl_switch_decoder cxlsd;
> };
>
