On Thu, Jan 27, 2022 at 4:27 PM Ben Widawsky <ben.widawsky@xxxxxxxxx> wrote:
>
> Regions are carved out of an addresses space which is claimed by top
> level decoders, and subsequently their children decoders. Regions are
s/children/descendant/
> created with a size and therefore must fit, with proper alignment, in
> that address space. The support for doing this fitting is handled by the
> driver automatically.
>
> As an example, a platform might configure a top level decoder to claim
> 1TB of address space @ 0x800000000 -> 0x10800000000; it would be
> possible to create M regions with appropriate alignment to occupy that
> address space. Each of those regions would have a host physical address
> somewhere in the range between 32G and 1.3TB, and the location will be
> determined by the logic added here.
>
> The request_region() usage is not strictly mandatory at this point as
> the actual handling of the address space is done with genpools. It is
> highly likely however that the resource/region APIs will become useful
> in the not too distant future.
More on this below, but I think resource APIs are critical for the
pre-existing / BIOS created region case and I have a feeling gen_pool
is not a good fit.
> All decoders manage a host physical address space while active. Only the
> root decoder has constraints on location and size. As a result, it makes
> most sense for the root decoder to be responsible for managing the
> entire address space, and mid-level decoders and endpoints can ask the
> root decoder for suballocations.
>
> Signed-off-by: Ben Widawsky <ben.widawsky@xxxxxxxxx>
> ---
> drivers/cxl/acpi.c | 30 ++++++++++++++++++++++++++++++
> drivers/cxl/cxl.h | 2 ++
> 2 files changed, 32 insertions(+)
>
> diff --git a/drivers/cxl/acpi.c b/drivers/cxl/acpi.c
> index d6dcb2b6af48..74681bfbf53c 100644
> --- a/drivers/cxl/acpi.c
> +++ b/drivers/cxl/acpi.c
> @@ -1,6 +1,7 @@
> // SPDX-License-Identifier: GPL-2.0-only
> /* Copyright(c) 2021 Intel Corporation. All rights reserved. */
> #include <linux/platform_device.h>
> +#include <linux/genalloc.h>
> #include <linux/module.h>
> #include <linux/device.h>
> #include <linux/kernel.h>
> @@ -73,6 +74,27 @@ static int cxl_acpi_cfmws_verify(struct device *dev,
> return 0;
> }
>
> +/*
> + * Every decoder while active has an address space that it is decoding. However,
> + * only the root level decoders have fixed host physical address space ranges.
> + */
> +static int cxl_create_cfmws_address_space(struct cxl_decoder *cxld,
> + struct acpi_cedt_cfmws *cfmws)
> +{
> + const int order = ilog2(SZ_256M * cxld->interleave_ways);
> + struct device *dev = &cxld->dev;
> + struct gen_pool *pool;
> +
> + pool = devm_gen_pool_create(dev, order, NUMA_NO_NODE, dev_name(dev));
The cxld dev is not a suitable devm host.
Moreover, the address space is a generic property of root decoders, it
belongs in the core not in cxl_acpi.
As for the data structure / APIs to manage the address space I'm not
sure gen_pool is the right answer, because the capacity tracking will
be done in terms of __request_region() and resource trees. The
infrastructure to keep the gen_pool aligned with the resource tree
drops away if there was an interface for allocating free space out of
a resource tree to augment the base API of requesting space with known
addresses. In fact, there is already the request_free_mem_region()
helper. Did you consider that vs gen_pool? Otherwise, how to solve the
problem of pre-populating the busy areas of the gen_pool relative to
capacity that the BIOS may have consumed out of the decoder range?
That comes for free with just walking decoders at boot and doing
__request_region() against the root decoders. Then the allocation
helper can just walk that free space similar to
request_free_mem_region().
> + if (IS_ERR(pool))
> + return PTR_ERR(pool);
> +
> + cxld->address_space = pool;
> +
> + return gen_pool_add(cxld->address_space, cfmws->base_hpa,
> + cfmws->window_size, NUMA_NO_NODE);
> +}
> +
> struct cxl_cfmws_context {
> struct device *dev;
> struct cxl_port *root_port;
> @@ -113,6 +135,14 @@ static int cxl_parse_cfmws(union acpi_subtable_headers *header, void *arg,
> cxld->interleave_ways = CFMWS_INTERLEAVE_WAYS(cfmws);
> cxld->interleave_granularity = CFMWS_INTERLEAVE_GRANULARITY(cfmws);
>
> + rc = cxl_create_cfmws_address_space(cxld, cfmws);
> + if (rc) {
> + dev_err(dev,
> + "Failed to create CFMWS address space for decoder\n");
> + put_device(&cxld->dev);
> + return 0;
> + }
> +
> rc = cxl_decoder_add(cxld, target_map);
> if (rc)
> put_device(&cxld->dev);
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index d1a8ca19c9ea..b300673072f5 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -251,6 +251,7 @@ enum cxl_decoder_type {
> * @flags: memory type capabilities and locking
> * @target_lock: coordinate coherent reads of the target list
> * @region_ida: allocator for region ids.
> + * @address_space: Used/free address space for regions.
> * @nr_targets: number of elements in @target
> * @target: active ordered target list in current decoder configuration
> */
> @@ -267,6 +268,7 @@ struct cxl_decoder {
> unsigned long flags;
> seqlock_t target_lock;
> struct ida region_ida;
> + struct gen_pool *address_space;
> int nr_targets;
> struct cxl_dport *target[];
> };
> --
> 2.35.0
>
