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platform/x86/intel/pmt: Cache the telemetry discovery header

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pmt_telem_header_decode() only needs the discovery header dwords, but it
currently decodes them by reading directly from entry->disc_table.

Cache the discovery header in intel_pmt_entry when the device is created
and have telemetry decode use the cached values instead of performing MMIO
reads at decode time.

The DVSEC discovery resource for a namespace is sized by its per-entry
entry_size (in dwords), which can be less than the 4-dword cache (e.g.
telemetry uses entry_size = 3, i.e. 12 bytes). Cap the memcpy_fromio()
to resource_size(disc_res) so the new cache does not read past the
mapped region. Any unread dwords stay zero from the zero-initialized
allocation of the containing struct.

This keeps the telemetry header decode path independent of how the
discovery data is backed and avoids baking a direct MMIO assumption into
the feature-specific decode logic.

Assisted-by: GitHub-Copilot:claude-opus-4.7
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://patch.msgid.link/f805e2ada52dc0661761cda7f692e76e6ea2d257.1781294741.git.david.e.box@linux.intel.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
This commit is contained in:
David E. Box 2026-06-12 14:01:46 -07:00 committed by Ilpo Järvinen
parent 4a87492cd1
commit 4dfc7dca6e
No known key found for this signature in database
GPG Key ID: 59AC4F6153E5CE31
3 changed files with 18 additions and 6 deletions
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11
drivers/platform/x86/intel/pmt/class.c
View File

@ -12,6 +12,7 @@
#include <linux/log2.h>
#include <linux/intel_vsec.h>
#include <linux/io-64-nonatomic-lo-hi.h>
#include <linux/minmax.h>
#include <linux/module.h>
#include <linux/mm.h>
#include <linux/pci.h>
@ -383,6 +384,16 @@ int intel_pmt_dev_create(struct intel_pmt_entry *entry, struct intel_pmt_namespa
if (IS_ERR(entry->disc_table))
return PTR_ERR(entry->disc_table);
/*
* The mapped discovery resource may be smaller than disc_header (its
* size is the namespace's DVSEC entry_size in dwords, which can be
* less than 4). Cap the copy to the actual resource size to avoid
* reading past the mapped region; any unread dwords stay zero from
* the zero-initialized allocation of the containing struct.
*/
memcpy_fromio(entry->disc_header, entry->disc_table,
min(sizeof(entry->disc_header), resource_size(disc_res)));
if (ns->pmt_pre_decode) {
ret = ns->pmt_pre_decode(intel_vsec_dev, entry);
if (ret)

1
drivers/platform/x86/intel/pmt/class.h
View File

@ -44,6 +44,7 @@ struct intel_pmt_entry {
struct telem_endpoint *ep;
struct pci_dev *pcidev;
struct intel_pmt_header header;
u32 disc_header[4];
struct bin_attribute pmt_bin_attr;
const struct attribute_group *attr_grp;
struct kobject *kobj;

12
drivers/platform/x86/intel/pmt/telemetry.c
View File

@ -72,16 +72,16 @@ static bool pmt_telem_region_overlaps(struct device *dev, u32 guid, u32 type)
static int pmt_telem_header_decode(struct intel_pmt_entry *entry,
struct device *dev)
{
void __iomem *disc_table = entry->disc_table;
struct intel_pmt_header *header = &entry->header;
u32 *disc_header = entry->disc_header;
header->access_type = TELEM_ACCESS(readl(disc_table));
header->guid = readl(disc_table + TELEM_GUID_OFFSET);
header->base_offset = readl(disc_table + TELEM_BASE_OFFSET);
header->access_type = TELEM_ACCESS(disc_header[0]);
header->guid = disc_header[1];
header->base_offset = disc_header[2];
/* Size is measured in DWORDS, but accessor returns bytes */
header->size = TELEM_SIZE(readl(disc_table));
header->telem_type = TELEM_TYPE(readl(entry->disc_table));
header->size = TELEM_SIZE(disc_header[0]);
header->telem_type = TELEM_TYPE(disc_header[0]);
return 0;
}