Re: [PATCH 06/26] cxl/port: Add Dynamic Capacity mode support to endpoint decoders

Jonathan Cameron
2024-04-04T08:32:03Z

On Sun, 24 Mar 2024 16:18:09 -0700
ira.weiny@intel.com wrote:

> From: Navneet Singh <navneet.singh@intel.com>
>
> Endpoint decoders which are used to map Dynamic Capacity must be
> configured to point to the correct Dynamic Capacity (DC) Region. The
> decoder mode currently represents the partition the decoder points to
> such as ram or pmem.
>
> Expand the mode to include DC regions [partitions].
>
> 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>
>
> ---
> Changes for v1:
> [iweiny: eliminate added gotos]
> [iweiny: Mark DC support for 6.10 kernel]
> ---
> Documentation/ABI/testing/sysfs-bus-cxl | 21 +++++++++++----------
> drivers/cxl/core/hdm.c | 19 +++++++++++++++++++
> drivers/cxl/core/port.c | 16 ++++++++++++++++
> 3 files changed, 46 insertions(+), 10 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-bus-cxl b/Documentation/ABI/testing/sysfs-bus-cxl
> index fff2581b8033..8b3efaf6563c 100644
> --- a/Documentation/ABI/testing/sysfs-bus-cxl
> +++ b/Documentation/ABI/testing/sysfs-bus-cxl
> @@ -316,23 +316,24 @@ Description:
>
>
> What: /sys/bus/cxl/devices/decoderX.Y/mode
> -Date: May, 2022
> -KernelVersion: v6.0
> +Date: May, 2022, June 2024
> +KernelVersion: v6.0, v6.10 (dcY)
> Contact: linux-cxl@vger.kernel.org
> Description:
> (RW) When a CXL decoder is of devtype "cxl_decoder_endpoint" it
> translates from a host physical address range, to a device local
> address range. Device-local address ranges are further split
> - into a 'ram' (volatile memory) range and 'pmem' (persistent
> - memory) range. The 'mode' attribute emits one of 'ram', 'pmem',
> - 'mixed', or 'none'. The 'mixed' indication is for error cases
> - when a decoder straddles the volatile/persistent partition
> - boundary, and 'none' indicates the decoder is not actively
> - decoding, or no DPA allocation policy has been set.
> + into a 'ram' (volatile memory) range, 'pmem' (persistent
> + memory) range, or Dynamic Capacity (DC) range. The 'mode'
> + attribute emits one of 'ram', 'pmem', 'dcY', 'mixed', or
> + 'none'. The 'mixed' indication is for error cases when a
> + decoder straddles the volatile/persistent partition boundary,

I love corners. What happen if no persistent and decoder straddles
volatile / dc0? Would only happen if the bios was having fun I think...

> + and 'none' indicates the decoder is not actively decoding, or
> + no DPA allocation policy has been set.
>
> 'mode' can be written, when the decoder is in the 'disabled'
> - state, with either 'ram' or 'pmem' to set the boundaries for the
> - next allocation.
> + state, with 'ram', 'pmem', or 'dcY' to set the boundaries for
> + the next allocation.
>
>
> What: /sys/bus/cxl/devices/decoderX.Y/dpa_resource
> diff --git a/drivers/cxl/core/hdm.c b/drivers/cxl/core/hdm.c
> index 66b8419fd0c3..e22b6f4f7145 100644
> --- a/drivers/cxl/core/hdm.c
> +++ b/drivers/cxl/core/hdm.c
> @@ -255,6 +255,14 @@ static void devm_cxl_dpa_release(struct cxl_endpoint_decoder *cxled)
> __cxl_dpa_release(cxled);
> }
>
> +static int dc_mode_to_region_index(enum cxl_decoder_mode mode)
> +{
> + if (mode < CXL_DECODER_DC0 || CXL_DECODER_DC7 < mode)
> + return -EINVAL;
> +
> + return mode - CXL_DECODER_DC0;
> +}
> +
> static int __cxl_dpa_reserve(struct cxl_endpoint_decoder *cxled,
> resource_size_t base, resource_size_t len,
> resource_size_t skipped)
> @@ -411,6 +419,7 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
> struct cxl_memdev *cxlmd = cxled_to_memdev(cxled);
> struct cxl_dev_state *cxlds = cxlmd->cxlds;
> struct device *dev = &cxled->cxld.dev;
> + int rc;
>
> guard(rwsem_write)(&cxl_dpa_rwsem);
> if (cxled->cxld.flags & CXL_DECODER_F_ENABLE)
> @@ -433,6 +442,16 @@ int cxl_dpa_set_mode(struct cxl_endpoint_decoder *cxled,
> return -ENXIO;
> }
> break;
> + case CXL_DECODER_DC0 ... CXL_DECODER_DC7:
> + rc = dc_mode_to_region_index(mode);
> + if (rc < 0)
> + return rc;

Can't fail, so you could not bother checking.. Seems very unlikely
that function will gain other error cases in the future.

> +
> + if (resource_size(&cxlds->dc_res[rc]) == 0) {
> + dev_dbg(dev, "no available dynamic capacity\n");
> + return -ENXIO;
> + }
> + break;
> default:
> dev_dbg(dev, "unsupported mode: %d\n", mode);
> return -EINVAL;
> diff --git a/drivers/cxl/core/port.c b/drivers/cxl/core/port.c
> index e59d9d37aa65..80c0651794eb 100644
> --- a/drivers/cxl/core/port.c
> +++ b/drivers/cxl/core/port.c
> @@ -208,6 +208,22 @@ static ssize_t mode_store(struct device *dev, struct device_attribute *attr,
> mode = CXL_DECODER_PMEM;
> else if (sysfs_streq(buf, "ram"))
> mode = CXL_DECODER_RAM;
> + else if (sysfs_streq(buf, "dc0"))
> + mode = CXL_DECODER_DC0;
> + else if (sysfs_streq(buf, "dc1"))
> + mode = CXL_DECODER_DC1;
> + else if (sysfs_streq(buf, "dc2"))
> + mode = CXL_DECODER_DC2;
> + else if (sysfs_streq(buf, "dc3"))
> + mode = CXL_DECODER_DC3;
> + else if (sysfs_streq(buf, "dc4"))
> + mode = CXL_DECODER_DC4;
> + else if (sysfs_streq(buf, "dc5"))
> + mode = CXL_DECODER_DC5;
> + else if (sysfs_streq(buf, "dc6"))
> + mode = CXL_DECODER_DC6;
> + else if (sysfs_streq(buf, "dc7"))
> + mode = CXL_DECODER_DC7;

Fully agree with the comment that a string + enum table and search
is probably appropriate here.

> else
> return -EINVAL;
>
>