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

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>

diff --git a/drivers/platform/x86/intel/pmt/class.c b/drivers/platform/x86/intel/pmt/class.c
index 7da8279b54f85c6e40365e945689223201811a9e..8d27f59d5bff0bf558bf5dd3898371435fe11fdf 100644 (file)
--- a/drivers/platform/x86/intel/pmt/class.c
+++ b/drivers/platform/x86/intel/pmt/class.c
@@ -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)

diff --git a/drivers/platform/x86/intel/pmt/class.h b/drivers/platform/x86/intel/pmt/class.h
index 8a0db0ef58c17ca26e4d64b43919fd5b9ccd5d83..84202fc7920c9b3d9b5d3614894c2a2a1c0f53a2 100644 (file)
--- a/drivers/platform/x86/intel/pmt/class.h
+++ b/drivers/platform/x86/intel/pmt/class.h
@@ -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;

diff --git a/drivers/platform/x86/intel/pmt/telemetry.c b/drivers/platform/x86/intel/pmt/telemetry.c
index d22f633638be76241bf6772264c515702454c7ea..953f35b6daecb66bd0d86b560e8718bbc2533a7c 100644 (file)
--- a/drivers/platform/x86/intel/pmt/telemetry.c
+++ b/drivers/platform/x86/intel/pmt/telemetry.c
@@ -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;
 }