Re: [PATCH v4 11/28] cxl/hdm: Add dynamic capacity size support to endpoint decoders

Jonathan Cameron
2024-10-10T12:45:38Z

On Mon, 07 Oct 2024 18:16:17 -0500
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
>
> To support Dynamic Capacity Devices (DCD) endpoint decoders will need to
> map DC partitions (regions). In addition to assigning the size of the
> DC partition, the decoder must assign any skip value from the previous
> decoder. This must be done within a contiguous DPA space.
>
> Two complications arise with Dynamic Capacity regions which did not
> exist with Ram and PMEM partitions. First, gaps in the DPA space can
> exist between and around the DC partitions. Second, the Linux resource
> tree does not allow a resource to be marked across existing nodes within
> a tree.
>
> For clarity, below is an example of an 60GB device with 10GB of RAM,
> 10GB of PMEM and 10GB for each of 2 DC partitions. The desired CXL
> mapping is 5GB of RAM, 5GB of PMEM, and 5GB of DC1.
>
> DPA RANGE
> (dpa_res)
> 0GB 10GB 20GB 30GB 40GB 50GB 60GB
> |----------|----------|----------|----------|----------|----------|
>
> RAM PMEM DC0 DC1
> (ram_res) (pmem_res) (dc_res[0]) (dc_res[1])
> |----------|----------| <gap> |----------| <gap> |----------|
>
> RAM PMEM DC1
> |XXXXX|----|XXXXX|----|----------|----------|----------|XXXXX-----|
> 0GB 5GB 10GB 15GB 20GB 30GB 40GB 50GB 60GB
>
> The previous skip resource between RAM and PMEM was always a child of
> the RAM resource and fit nicely [see (S) below]. Because of this
> simplicity this skip resource reference was not stored in any CXL state.
> On release the skip range could be calculated based on the endpoint
> decoders stored values.
>
> Now when DC1 is being mapped 4 skip resources must be created as
> children. One for the PMEM resource (A), two of the parent DPA resource
> (B,D), and one more child of the DC0 resource (C).
>
> 0GB 10GB 20GB 30GB 40GB 50GB 60GB
> |----------|----------|----------|----------|----------|----------|
> | |
> |----------|----------| | |----------| | |----------|
> | | | | |
> (S) (A) (B) (C) (D)
> v v v v v
> |XXXXX|----|XXXXX|----|----------|----------|----------|XXXXX-----|
> skip skip skip skip skip
>
> Expand the calculation of DPA free space and enhance the logic to
> support this more complex skipping. To track the potential of multiple
> skip resources an xarray is attached to the endpoint decoder. The
> existing algorithm between RAM and PMEM is consolidated within the new
> one to streamline the code even though the result is the storage of a
> single skip resource in the xarray.
>
> Signed-off-by: Navneet Singh <navneet.singh@intel.com>
> Co-developed-by: Ira Weiny <ira.weiny@intel.com>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
One trivial comment inline.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
>
> ---
> Changes:
> [djiang: s/skip_res/skip_xa/]
> ---
> drivers/cxl/core/hdm.c | 196 ++++++++++++++++++++++++++++++++++++++++++++----
> drivers/cxl/core/port.c | 2 +
> drivers/cxl/cxl.h | 2 +
> 3 files changed, 184 insertions(+), 16 deletions(-)
>
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 3df10517a327..8c7f941eaba1 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -223,6 +223,25 @@ void cxl_dpa_debug(struct seq_file *file, struct cxl_dev_state *cxlds)
> }
> EXPORT_SYMBOL_NS_GPL(cxl_dpa_debug, CXL);
>
> +static void cxl_skip_release(struct cxl_endpoint_decoder *cxled)
> +{
> + struct cxl_dev_state *cxlds = cxled_to_memdev(cxled)->cxlds;
> + struct cxl_port *port = cxled_to_port(cxled);
> + struct device *dev = &port->dev;
> + unsigned long index;
> + void *entry;
> +
> + xa_for_each(&cxled->skip_xa, index, entry) {
> + struct resource *res = entry;

struct resource *res;

xa_for_each(&cxled->skip_xa, index, res) {

as can always cast form a pointer to a void *
and avoiding the extra local variable is a nice to have.

> +
> + dev_dbg(dev, "decoder%d.%d: releasing skipped space; %pr\n",
> + port->id, cxled->cxld.id, res);
> + __release_region(&cxlds->dpa_res, res->start,
> + resource_size(res));
> + xa_erase(&cxled->skip_xa, index);
> + }
> +}