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Message-ID: <eabbe979-f6d1-42fb-880e-66b1f9a4e617@amd.com>
Date: Mon, 7 Apr 2025 14:25:08 +0100
From: Alejandro Lucero Palau <alucerop@....com>
To: Jonathan Cameron <Jonathan.Cameron@...wei.com>,
alejandro.lucero-palau@....com
Cc: linux-cxl@...r.kernel.org, netdev@...r.kernel.org,
dan.j.williams@...el.com, edward.cree@....com, davem@...emloft.net,
kuba@...nel.org, pabeni@...hat.com, edumazet@...gle.com, dave.jiang@...el.com
Subject: Re: [PATCH v12 11/23] cxl: define a driver interface for HPA free
space enumeration
On 4/4/25 17:37, Jonathan Cameron wrote:
> On Mon, 31 Mar 2025 15:45:43 +0100
> alejandro.lucero-palau@....com wrote:
>
>> From: Alejandro Lucero <alucerop@....com>
>>
>> CXL region creation involves allocating capacity from device DPA
>> (device-physical-address space) and assigning it to decode a given HPA
>> (host-physical-address space). Before determining how much DPA to
>> allocate the amount of available HPA must be determined. Also, not all
>> HPA is created equal, some specifically targets RAM, some target PMEM,
>> some is prepared for device-memory flows like HDM-D and HDM-DB, and some
>> is host-only (HDM-H).
>>
>> Wrap all of those concerns into an API that retrieves a root decoder
>> (platform CXL window) that fits the specified constraints and the
>> capacity available for a new region.
>>
>> Add a complementary function for releasing the reference to such root
>> decoder.
>>
>> Based on https://lore.kernel.org/linux-cxl/168592159290.1948938.13522227102445462976.stgit@dwillia2-xfh.jf.intel.com/
>>
>> Signed-off-by: Alejandro Lucero <alucerop@....com>
>> ---
>> drivers/cxl/core/region.c | 160 ++++++++++++++++++++++++++++++++++++++
>> drivers/cxl/cxl.h | 3 +
>> include/cxl/cxl.h | 11 ++-
>> 3 files changed, 173 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/cxl/core/region.c b/drivers/cxl/core/region.c
>> index c3f4dc244df7..59fb51ff8922 100644
>> --- a/drivers/cxl/core/region.c
>> +++ b/drivers/cxl/core/region.c
>> @@ -695,6 +695,166 @@ static int free_hpa(struct cxl_region *cxlr)
>> return 0;
>> }
>> +static int find_max_hpa(struct device *dev, void *data)
>> +{
>> + struct cxlrd_max_context *ctx = data;
>> + struct cxl_switch_decoder *cxlsd;
>> + struct cxl_root_decoder *cxlrd;
>> + struct resource *res, *prev;
>> + struct cxl_decoder *cxld;
>> + resource_size_t max;
>> + int found = 0;
>> +
>> + if (!is_root_decoder(dev))
>> + return 0;
>> +
>> + cxlrd = to_cxl_root_decoder(dev);
>> + cxlsd = &cxlrd->cxlsd;
>> + cxld = &cxlsd->cxld;
>> + if ((cxld->flags & ctx->flags) != ctx->flags) {
> Hmm. Is this a subset test?
> if (!(cxld->flags & ~ctx->flags)) or something like that?
> Or just use bitmap_subset() on it if they are both unsigned longs.
>
I guess bitmap_subset can be used since the cxld flags could contain
more than those required by the caller.
I'll use it.
>> + dev_dbg(dev, "flags not matching: %08lx vs %08lx\n",
>> + cxld->flags, ctx->flags);
>> + return 0;
>> + }
>> +
>> + for (int i = 0; i < ctx->interleave_ways; i++) {
>> + for (int j = 0; j < ctx->interleave_ways; j++) {
>> + if (ctx->host_bridges[i] == cxlsd->target[j]->dport_dev) {
>> + found++;
>> + break;
>> + }
>> + }
>> + }
>> +
>> + if (found != ctx->interleave_ways) {
>> + dev_dbg(dev, "Not enough host bridges found(%d) for interleave ways requested (%d)\n",
>> + found, ctx->interleave_ways);
>> + return 0;
>> + }
>> +
>> + /*
>> + * Walk the root decoder resource range relying on cxl_region_rwsem to
>> + * preclude sibling arrival/departure and find the largest free space
>> + * gap.
>> + */
>> + lockdep_assert_held_read(&cxl_region_rwsem);
>> + max = 0;
>> + res = cxlrd->res->child;
>> +
>> + /* With no resource child the whole parent resource is available */
>> + if (!res)
>> + max = resource_size(cxlrd->res);
>> + else
>> + max = 0;
> max is already 0 in this path.
>
Right. I'll remove this one.
Thanks!
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