Re: [PATCH V6 10/10] cxl/cdat: Parse out DSMAS data from CDAT table

Ben Widawsky
2022-02-01T19:05:38Z

On 22-01-31 23:19:52, ira.weiny@intel.com wrote:
> From: Ira Weiny <ira.weiny@intel.com>
>
> CXL memory devices need the information in the Device Scoped Memory
> Affinity Structure (DSMAS). This information is contained within the
> CDAT table buffer which is already read and cached.
>
> Parse and cache DSMAS data from the CDAT table. Store this data in
> unmarshaled struct dsmas data structures for ease of use.
>
> Signed-off-by: Ira Weiny <ira.weiny@intel.com>
>
> ---
> Changes from V5
> Fix up sparse warnings
> Split out cdat_hdr_valid()
> Update cdat_hdr_valid()
> Remove revision and cs field parsing
> There is no point in these
> Add seq check and debug print.
> From Jonathan
> Add spaces around '+' and '/'
> use devm_krealloc() for dmas_ary
>
> Changes from V4
> New patch
> ---
> drivers/cxl/cdat.h | 21 ++++++++++++
> drivers/cxl/core/memdev.c | 70 +++++++++++++++++++++++++++++++++++++++
> 2 files changed, 91 insertions(+)
>
> diff --git a/drivers/cxl/cdat.h b/drivers/cxl/cdat.h
> index a7725d26f2d2..f8c126190d18 100644
> --- a/drivers/cxl/cdat.h
> +++ b/drivers/cxl/cdat.h
> @@ -83,17 +83,38 @@
> #define CDAT_SSLBIS_ENTRY_PORT_Y(entry, i) (((entry)[4 + (i) * 2] & 0xffff0000) >> 16)
> #define CDAT_SSLBIS_ENTRY_LAT_OR_BW(entry, i) ((entry)[4 + (i) * 2 + 1] & 0x0000ffff)
>
> +/**
> + * struct cxl_dsmas - host unmarshaled version of DSMAS data
> + *
> + * As defined in the Coherent Device Attribute Table (CDAT) specification this
> + * represents a single DSMAS entry in that table.
> + *
> + * @dpa_base: The lowest DPA address associated with this DSMAD
> + * @dpa_length: Length in bytes of this DSMAD
> + * @non_volatile: If set, the memory region represents Non-Volatile memory
> + */
> +struct cxl_dsmas {
> + u64 dpa_base;
> + u64 dpa_length;
> + /* Flags */
> + u8 non_volatile:1;
> +};
> +
> /**
> * struct cxl_cdat - CXL CDAT data
> *
> * @table: cache of CDAT table
> * @length: length of cached CDAT table
> * @seq: Last read Sequence number of the CDAT table
> + * @dsmas_ary: Array of DSMAS entries as parsed from the CDAT table
> + * @nr_dsmas: Number of entries in dsmas_ary
> */
> struct cxl_cdat {
> void *table;
> size_t length;
> u32 seq;
> + struct cxl_dsmas *dsmas_ary;
> + int nr_dsmas;
> };
>
> #endif /* !__CXL_CDAT_H__ */
> diff --git a/drivers/cxl/core/memdev.c b/drivers/cxl/core/memdev.c
> index 11d721c56f08..32342a15e991 100644
> --- a/drivers/cxl/core/memdev.c
> +++ b/drivers/cxl/core/memdev.c
> @@ -6,6 +6,7 @@
> #include <linux/idr.h>
> #include <linux/pci.h>
> #include <cxlmem.h>
> +#include "cdat.h"
> #include "core.h"
>
> static DECLARE_RWSEM(cxl_memdev_rwsem);
> @@ -386,6 +387,71 @@ static int read_cdat_data(struct cxl_memdev *cxlmd,
> return rc;
> }
>
> +static int parse_dsmas(struct cxl_memdev *cxlmd)
> +{
> + struct cxl_dsmas *dsmas_ary = NULL;
> + u32 *data = cxlmd->cdat.table;
> + int bytes_left = cxlmd->cdat.length;
> + int nr_dsmas = 0;
> +
> + if (!data)
> + return -ENXIO;
> +
> + /* Skip header */
> + data += CDAT_HEADER_LENGTH_DW;
> + bytes_left -= CDAT_HEADER_LENGTH_BYTES;
> +
> + while (bytes_left > 0) {
> + u32 *cur_rec = data;
> + u8 type = FIELD_GET(CDAT_STRUCTURE_DW0_TYPE, cur_rec[0]);
> + u16 length = FIELD_GET(CDAT_STRUCTURE_DW0_LENGTH, cur_rec[0]);
> +
> + if (type == CDAT_STRUCTURE_DW0_TYPE_DSMAS) {
> + struct cxl_dsmas *new_ary;
> + u8 flags;
> +
> + new_ary = devm_krealloc(&cxlmd->dev, dsmas_ary,
> + sizeof(*dsmas_ary) * (nr_dsmas + 1),
> + GFP_KERNEL);
> + if (!new_ary) {
> + dev_err(&cxlmd->dev,
> + "Failed to allocate memory for DSMAS data\n");
> + return -ENOMEM;
> + }

One thought here - it looks like there are at most 256 DSMAS entries. You could
allocate the full 256 up front, and then realloc *down* to the actual number.

> + dsmas_ary = new_ary;
> +
> + flags = FIELD_GET(CDAT_DSMAS_DW1_FLAGS, cur_rec[1]);
> +
> + dsmas_ary[nr_dsmas].dpa_base = CDAT_DSMAS_DPA_OFFSET(cur_rec);
> + dsmas_ary[nr_dsmas].dpa_length = CDAT_DSMAS_DPA_LEN(cur_rec);
> + dsmas_ary[nr_dsmas].non_volatile = CDAT_DSMAS_NON_VOLATILE(flags);
> +
> + dev_dbg(&cxlmd->dev, "DSMAS %d: %llx:%llx %s\n",
> + nr_dsmas,
> + dsmas_ary[nr_dsmas].dpa_base,
> + dsmas_ary[nr_dsmas].dpa_base +
> + dsmas_ary[nr_dsmas].dpa_length,
> + (dsmas_ary[nr_dsmas].non_volatile ?
> + "Persistent" : "Volatile")
> + );
> +
> + nr_dsmas++;
> + }
> +
> + data += (length / sizeof(u32));
> + bytes_left -= length;
> + }
> +
> + if (nr_dsmas == 0)
> + return -ENXIO;

Hmm is there documentation that suggests a DSMAS must be implemented? Could this
just return 0? I'd put maybe dev_dbg here if it's unexpected but not a failure
and return success.

> +
> + dev_dbg(&cxlmd->dev, "Found %d DSMAS entries\n", nr_dsmas);
> + cxlmd->cdat.dsmas_ary = dsmas_ary;
> + cxlmd->cdat.nr_dsmas = nr_dsmas;
> +
> + return 0;
> +}
> +
> struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
> {
> struct cxl_memdev *cxlmd;
> @@ -407,6 +473,10 @@ struct cxl_memdev *devm_cxl_add_memdev(struct cxl_dev_state *cxlds)
> if (rc)
> goto err;
>
> + rc = parse_dsmas(cxlmd);
> + if (rc)
> + dev_warn(dev, "No DSMAS data found: %d\n", rc);
> +
> /*
> * Activate ioctl operations, no cxl_memdev_rwsem manipulation
> * needed as this is ordered with cdev_add() publishing the device.
> --
> 2.31.1
>