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

Ira Weiny
2022-02-01T22:37:20Z

On Tue, Feb 01, 2022 at 11:05:32AM -0800, Widawsky, Ben wrote:
> 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.

For this call I was not envisioning this as an error. I wanted to leave it up
to the caller.

I think it would make more sense to return the number of DSMAS' found or
negative errno on failure...

I'll clean it up. Including below...

>
> > +
> > + 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);
> > +

This was changed to dev_warn() because I think here we do expect dsmas data?
Don't we?

Thanks,
Ira

> > /*
> > * Activate ioctl operations, no cxl_memdev_rwsem manipulation
> > * needed as this is ordered with cdev_add() publishing the device.
> > --
> > 2.31.1
> >