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| author | Dan Williams <dan.j.williams@intel.com> | 2022-08-05 23:27:51 +0300 |
|---|---|---|
| committer | Dan Williams <dan.j.williams@intel.com> | 2022-08-06 02:10:04 +0300 |
| commit | 4d8e4ea5bb396897111e8a740201bfd3c5926170 (patch) | |
| tree | 86599027ce1169a658219aaf71800d1165f9f8d1 /drivers/cxl | |
| parent | 298d44d04b2ba97824c3dadd1dbf7c154a2a86e2 (diff) | |
| download | linux-4d8e4ea5bb396897111e8a740201bfd3c5926170.tar.xz | |
cxl/region: Disallow region granularity != window granularity
The endpoint decode granularity must be <= the window granularity
otherwise capacity in the endpoints is lost in the decode. Consider an
attempt to have a region granularity of 512 with 4 devices within a
window that maps 2 host bridges at a granularity of 256 bytes:
HPA DPA Offset HB Port EP
0x0 0x0 0 0 0
0x100 0x0 1 0 2
0x200 0x100 0 0 0
0x300 0x100 1 0 2
0x400 0x200 0 1 1
0x500 0x200 1 1 3
0x600 0x300 0 1 1
0x700 0x300 1 1 3
0x800 0x400 0 0 0
0x900 0x400 1 0 2
0xA00 0x500 0 0 0
0xB00 0x500 1 0 2
Notice how endpoint0 maps HPA 0x0 and 0x200 correctly, but then at HPA
0x800 it results in DPA 0x200-0x400 on being skipped.
Fix this by restricing the region granularity to be equal to the window
granularity resulting in the following for a x4 region under a x2 window
at a granularity of 256.
HPA DPA Offset HB Port EP
0x0 0x0 0 0 0
0x100 0x0 1 0 2
0x200 0x0 0 1 1
0x300 0x0 1 1 3
0x400 0x100 0 0 0
0x500 0x100 1 0 2
0x600 0x100 0 1 1
0x700 0x100 1 1 3
Not that it ever made practical sense to support region granularity >
window granularity. The window rotates host bridges causing endpoints to
never see a consecutive stream of requests at the desired granularity
without breaks to issue cycles to the other host bridge.
Fixes: 80d10a6cee05 ("cxl/region: Add interleave geometry attributes")
Cc: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Reviewed-by: Vishal Verma <vishal.l.verma@intel.com>
Reviewed-by: Ira Weiny <ira.weiny@intel.com>
Link: https://lore.kernel.org/r/165973127171.1526540.9923273539049172976.stgit@dwillia2-xfh.jf.intel.com
Signed-off-by: Dan Williams <dan.j.williams@intel.com>
Diffstat (limited to 'drivers/cxl')
| -rw-r--r-- | drivers/cxl/core/region.c | 13 |
1 files changed, 7 insertions, 6 deletions
diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c index 641bc6344a4a..401148016978 100644 --- a/drivers/cxl/core/region.c +++ b/drivers/cxl/core/region.c @@ -395,13 +395,14 @@ static ssize_t interleave_granularity_store(struct device *dev, return rc; /* - * Disallow region granularity less than root granularity to - * simplify the implementation. Otherwise, region's with a - * granularity less than the root interleave result in needing - * multiple endpoints to support a single slot in the - * interleave. + * When the host-bridge is interleaved, disallow region granularity != + * root granularity. Regions with a granularity less than the root + * interleave result in needing multiple endpoints to support a single + * slot in the interleave (possible to suport in the future). Regions + * with a granularity greater than the root interleave result in invalid + * DPA translations (invalid to support). */ - if (val < cxld->interleave_granularity) + if (cxld->interleave_ways > 1 && val != cxld->interleave_granularity) return -EINVAL; rc = down_write_killable(&cxl_region_rwsem); |