From: Dan Williams Date: Fri, 5 Aug 2022 20:27:51 +0000 (-0700) Subject: cxl/region: Disallow region granularity != window granularity X-Git-Tag: v6.1-rc5~632^2~1 X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=4d8e4ea5bb396897111e8a740201bfd3c5926170;p=platform%2Fkernel%2Flinux-starfive.git 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 Reviewed-by: Vishal Verma Reviewed-by: Ira Weiny Link: https://lore.kernel.org/r/165973127171.1526540.9923273539049172976.stgit@dwillia2-xfh.jf.intel.com Signed-off-by: Dan Williams --- diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c index 641bc6344..4011480 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);