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De Francesco" , Terry Bowman , Joshua Hahn References: <20250912144514.526441-1-rrichter@amd.com> <20250912144514.526441-9-rrichter@amd.com> <20250915114614.000053f1@huawei.com> Content-Language: en-US From: Dave Jiang In-Reply-To: Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit On 9/17/25 1:51 PM, Gregory Price wrote: > On Mon, Sep 15, 2025 at 11:46:14AM +0100, Jonathan Cameron wrote: >>> + /* >>> + * Since translated addresses include the interleaving >>> + * offsets, align the range to 256 MB. >> >> So we pass in an HPA range without interleaving offsets and get back >> one with them? Is that unavoidable, or can we potentially push >> this bit into the callback? Probably with separate callbacks to >> get the interleave details. >> >> Overall I'm not really following what is going on here. Maybe >> some ascii art would help? >> > > The endpoints in this case are encoded with "normalized" (base-0) with > a size of only the memory they provide. As a result, the decoder > interleave settings will always be passthrough (iw=1, ig=ignored). > > This chunk translates the normalized address region to the relevant SPA > region, and translates the IW/IG to what it actually is (i.e. what it > *would have* been on a "normal" system). > > Took me a while when i originally reviewed and tested this set. > > Example - this is how you'd expect a real system supported by this code > to be programmed: > > region { > .start = 0x20000000 > .end = 0x3fffffff > .iw = 2 > .ig = 256 > } > > endpoint1_decoder { > .start = 0x0 > .end = 0xfffffff > .iw = 1 > .ig = 256 > } > > endpoint2_decoder { > .start = 0x0 > .end = 0xfffffff > .iw = 1 > .ig = 256 > } > > when you do the translation from either decoder's hpa start/end, > you want the following output: > > range { > .start = 0x20000000 > .end = 0x3fffffff > .iw = 2 > .ig = 256 > } > > If you assume a "normal" system - this is the settings the decoders > would have been programmed with in the first place. > > You have to do the alignment because the translation function (may) > only work on granularity alignment. > > Example: > endpoint1->to_hpa(0) => 0x0 > endpoint1->to_hpa(0xfffffff) => 0xffffe00 > endpoint2->to_hpa(0) => 0x100 > endpoint2->to_hpa(0xfffffff) => 0xfffff00 > > So this code applies the appropriate alignment and returns the > translated iw/ig for use elsewhere in the stack when validating the rest > of the decoders. Having this explanation added to the Conventions document would be good to have. > > (haven't gotten to later commits, but iirc it was eventually used) > > ~Gregory > >>> + */ >>> + range.start = ALIGN_DOWN(range.start, SZ_256M); >>> + range.end = ALIGN(range.end, SZ_256M) - 1; >>> + >>> + spa_len = range_len(&range); >>> + if (!len || !spa_len || spa_len % len) { >>> + dev_warn(&port->dev, >>> + "CXL address translation: HPA range not contiguous: %#llx-%#llx:%#llx-%#llx(%s)\n", >>> + range.start, range.end, ctx->hpa_range.start, >>> + ctx->hpa_range.end, dev_name(&cxld->dev)); >>> + return -ENXIO; >>> + } >>> + >>> + ways = spa_len / len; >>> + gran = SZ_256; >>> +