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Message-ID: <5b3f6c11-c51c-4f24-98c1-3d5ceadf4278@intel.com>
Date: Fri, 27 Jun 2025 13:46:16 -0700
From: Dave Jiang <dave.jiang@...el.com>
To: alejandro.lucero-palau@....com, linux-cxl@...r.kernel.org,
netdev@...r.kernel.org, dan.j.williams@...el.com, edward.cree@....com,
davem@...emloft.net, kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com
Cc: Alejandro Lucero <alucerop@....com>,
Ben Cheatham <benjamin.cheatham@....com>,
Jonathan Cameron <Jonathan.Cameron@...wei.com>
Subject: Re: [PATCH v17 13/22] cxl: Define a driver interface for DPA
allocation
On 6/24/25 7:13 AM, alejandro.lucero-palau@....com wrote:
> From: Alejandro Lucero <alucerop@....com>
>
> Region creation involves finding available DPA (device-physical-address)
> capacity to map into HPA (host-physical-address) space.
>
> In order to support CXL Type2 devices, define an API, cxl_request_dpa(),
> that tries to allocate the DPA memory the driver requires to operate.The
> memory requested should not be bigger than the max available HPA obtained
> previously with cxl_get_hpa_freespace.
cxl_get_hpa_freespace()
>
> Based on https://lore.kernel.org/linux-cxl/168592158743.1948938.7622563891193802610.stgit@dwillia2-xfh.jf.intel.com/
>
> Signed-off-by: Alejandro Lucero <alucerop@....com>
> Reviewed-by: Ben Cheatham <benjamin.cheatham@....com>
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@...wei.com>
> ---
> drivers/cxl/core/hdm.c | 93 ++++++++++++++++++++++++++++++++++++++++++
> drivers/cxl/cxl.h | 2 +
> include/cxl/cxl.h | 5 +++
> 3 files changed, 100 insertions(+)
>
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 70cae4ebf8a4..b17381e49836 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -3,6 +3,7 @@
> #include <linux/seq_file.h>
> #include <linux/device.h>
> #include <linux/delay.h>
> +#include <cxl/cxl.h>
>
> #include "cxlmem.h"
> #include "core.h"
> @@ -546,6 +547,13 @@ resource_size_t cxl_dpa_resource_start(struct cxl_endpoint_decoder *cxled)
> return base;
> }
>
> +/**
> + * cxl_dpa_free - release DPA (Device Physical Address)
> + *
> + * @cxled: endpoint decoder linked to the DPA
> + *
> + * Returns 0 or error.
> + */
> int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
> {
> struct cxl_port *port = cxled_to_port(cxled);
> @@ -572,6 +580,7 @@ int cxl_dpa_free(struct cxl_endpoint_decoder *cxled)
> devm_cxl_dpa_release(cxled);
> return 0;
> }
> +EXPORT_SYMBOL_NS_GPL(cxl_dpa_free, "CXL");
>
> int cxl_dpa_set_part(struct cxl_endpoint_decoder *cxled,
> enum cxl_partition_mode mode)
> @@ -686,6 +695,90 @@ int cxl_dpa_alloc(struct cxl_endpoint_decoder *cxled, unsigned long long size)
> return devm_add_action_or_reset(&port->dev, cxl_dpa_release, cxled);
> }
>
> +static int find_free_decoder(struct device *dev, const void *data)
> +{
> + struct cxl_endpoint_decoder *cxled;
> + struct cxl_port *port;
> +
> + if (!is_endpoint_decoder(dev))
> + return 0;
> +
> + cxled = to_cxl_endpoint_decoder(dev);
> + port = cxled_to_port(cxled);
> +
> + if (cxled->cxld.id != port->hdm_end + 1)
> + return 0;
> +
> + return 1;
return cxled->cxld.id == port->hdm_end + 1;
> +}
> +
> +static struct cxl_endpoint_decoder *
> +cxl_find_free_decoder(struct cxl_memdev *cxlmd)
> +{
> + struct cxl_port *endpoint = cxlmd->endpoint;
> + struct device *dev;
> +
> + scoped_guard(rwsem_read, &cxl_dpa_rwsem) {
Probably ok to just use guard() here
> + dev = device_find_child(&endpoint->dev, NULL,
> + find_free_decoder);
> + }
> + if (dev)
> + return to_cxl_endpoint_decoder(dev);
> +
> + return NULL;
> +}
> +
> +/**
> + * cxl_request_dpa - search and reserve DPA given input constraints
> + * @cxlmd: memdev with an endpoint port with available decoders
> + * @mode: DPA operation mode (ram vs pmem)
> + * @alloc: dpa size required
> + *
> + * Returns a pointer to a cxl_endpoint_decoder struct or an error
> + *
> + * Given that a region needs to allocate from limited HPA capacity it
> + * may be the case that a device has more mappable DPA capacity than
> + * available HPA. The expectation is that @alloc is a driver known
> + * value based on the device capacity but it could not be available
> + * due to HPA constraints.
> + *
> + * Returns a pinned cxl_decoder with at least @alloc bytes of capacity
> + * reserved, or an error pointer. The caller is also expected to own the
> + * lifetime of the memdev registration associated with the endpoint to
> + * pin the decoder registered as well.
> + */
> +struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
> + enum cxl_partition_mode mode,
> + resource_size_t alloc)
> +{
> + struct cxl_endpoint_decoder *cxled __free(put_cxled) =
> + cxl_find_free_decoder(cxlmd);
> + struct device *cxled_dev;
> + int rc;
> +
> + if (!IS_ALIGNED(alloc, SZ_256M))
> + return ERR_PTR(-EINVAL);
> +
> + if (!cxled) {
> + rc = -ENODEV;
> + goto err;
return ERR_PTR(-ENODEV);
cxled_dev is not set here. In fact it's never set anywhere. the put_device() later will fail. Although the __free() should take care of it right? The err path isn't necessary?
> + }
> +
> + rc = cxl_dpa_set_part(cxled, mode);
> + if (rc)
> + goto err;
> +
> + rc = cxl_dpa_alloc(cxled, alloc);
> + if (rc)
> + goto err;
> +
> + return cxled;
return no_free_ptr(cxled);
DJ
> +err:
> + put_device(cxled_dev);
> + return ERR_PTR(rc);
> +}
> +EXPORT_SYMBOL_NS_GPL(cxl_request_dpa, "CXL");
> +
> static void cxld_set_interleave(struct cxl_decoder *cxld, u32 *ctrl)
> {
> u16 eig;
> diff --git a/drivers/cxl/cxl.h b/drivers/cxl/cxl.h
> index 3af8821f7c15..6e724a8440f5 100644
> --- a/drivers/cxl/cxl.h
> +++ b/drivers/cxl/cxl.h
> @@ -636,6 +636,8 @@ void put_cxl_root(struct cxl_root *cxl_root);
> DEFINE_FREE(put_cxl_root, struct cxl_root *, if (_T) put_cxl_root(_T))
>
> DEFINE_FREE(put_cxl_port, struct cxl_port *, if (!IS_ERR_OR_NULL(_T)) put_device(&_T->dev))
> +DEFINE_FREE(put_cxled, struct cxl_endpoint_decoder *, if (_T) put_device(&_T->cxld.dev))
> +
> int devm_cxl_enumerate_ports(struct cxl_memdev *cxlmd);
> void cxl_bus_rescan(void);
> void cxl_bus_drain(void);
> diff --git a/include/cxl/cxl.h b/include/cxl/cxl.h
> index dd37b1d88454..a2f3e683724a 100644
> --- a/include/cxl/cxl.h
> +++ b/include/cxl/cxl.h
> @@ -7,6 +7,7 @@
>
> #include <linux/node.h>
> #include <linux/ioport.h>
> +#include <linux/range.h>
> #include <cxl/mailbox.h>
>
> /**
> @@ -247,4 +248,8 @@ struct cxl_root_decoder *cxl_get_hpa_freespace(struct cxl_memdev *cxlmd,
> unsigned long flags,
> resource_size_t *max);
> void cxl_put_root_decoder(struct cxl_root_decoder *cxlrd);
> +struct cxl_endpoint_decoder *cxl_request_dpa(struct cxl_memdev *cxlmd,
> + enum cxl_partition_mode mode,
> + resource_size_t alloc);
> +int cxl_dpa_free(struct cxl_endpoint_decoder *cxled);
> #endif /* __CXL_CXL_H__ */
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