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

Jonathan Cameron
2022-02-04T13:41:51Z

On Tue, 1 Feb 2022 14:37:17 -0800
Ira Weiny <ira.weiny@intel.com> wrote:

> 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.

Gut feeling is there will be 1 or 2 on at typical device, so not sure it is worth
a large allocation and shrink.
Plus not a hot path and this is easy to follow.