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

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Message-ID: <20220204134142.0000170e@Huawei.com>
Date:   Fri, 4 Feb 2022 13:41:42 +0000
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     Ira Weiny <ira.weiny@...el.com>
CC:     Ben Widawsky <ben.widawsky@...el.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Alison Schofield" <alison.schofield@...el.com>,
        Vishal Verma <vishal.l.verma@...el.com>,
        <linux-kernel@...r.kernel.org>, <linux-cxl@...r.kernel.org>,
        <linux-pci@...r.kernel.org>
Subject: Re: [PATCH V6 10/10] cxl/cdat: Parse out DSMAS data from CDAT table

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

> On Tue, Feb 01, 2022 at 11:05:32AM -0800, Widawsky, Ben wrote:
> > On 22-01-31 23:19:52, ira.weiny@...el.com wrote:  
> > > From: Ira Weiny <ira.weiny@...el.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@...el.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.