[PATCH 19/22] platform/x86/intel/pmc/ssram: Refactor memory barrier for reentrant probe

David E. Box
2026-03-13T01:52:30Z

From: Xi Pardee <xi.pardee@linux.intel.com>

Switch the readiness synchronization from a global device_probed flag to
per-index devid publication. This is required because a subsequent patch
makes probe reentrant, so a single global flag can no longer reliably
signal completion.

Signed-off-by: Xi Pardee <xi.pardee@linux.intel.com>
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
---
.../platform/x86/intel/pmc/ssram_telemetry.c | 34 ++++++++-----------
1 file changed, 14 insertions(+), 20 deletions(-)

diff --git a/drivers/platform/x86/intel/pmc/ssram_telemetry.c b/drivers/platform/x86/intel/pmc/ssram_telemetry.c
index 7db98037c521..246efdcf6950 100644
--- a/drivers/platform/x86/intel/pmc/ssram_telemetry.c
+++ b/drivers/platform/x86/intel/pmc/ssram_telemetry.c
@@ -37,7 +37,6 @@ static const struct ssram_type pci_main = {
};

static struct pmc_ssram_telemetry pmc_ssram_telems[3];
-static bool device_probed;

static inline u64 get_base(void __iomem *addr, u32 offset)
{
@@ -52,8 +51,13 @@ static void pmc_ssram_get_devid_pwrmbase(void __iomem *ssram, unsigned int pmc_i
pwrm_base = get_base(ssram, SSRAM_PWRM_OFFSET);
devid = readw(ssram + SSRAM_DEVID_OFFSET);

- pmc_ssram_telems[pmc_idx].devid = devid;
pmc_ssram_telems[pmc_idx].base_addr = pwrm_base;
+ /*
+ * Memory barrier is used to ensure the correct write order between base_addr
+ * and devid.
+ */
+ smp_wmb();
+ pmc_ssram_telems[pmc_idx].devid = devid;
}

static int
@@ -151,32 +155,28 @@ static int pmc_ssram_telemetry_pci_init(struct pci_dev *pcidev)
* * 0 - Success
* * -EAGAIN - Probe function has not finished yet. Try again.
* * -EINVAL - Invalid pmc_idx
- * * -ENODEV - PMC device is not available
*/
int pmc_ssram_telemetry_get_pmc_info(unsigned int pmc_idx,
struct pmc_ssram_telemetry *pmc_ssram_telemetry)
{
+ if (pmc_idx >= MAX_NUM_PMC)
+ return -EINVAL;
+
/*
* PMCs are discovered in probe function. If this function is called before
- * probe function complete, the result would be invalid. Use device_probed
- * variable to avoid this case. Return -EAGAIN to inform the consumer to call
+ * probe function complete, the result would be invalid. Use devid to avoid
+ * this case. Return -EAGAIN to inform the consumer to call
* again later.
*/
- if (!device_probed)
+ if (!pmc_ssram_telems[pmc_idx].devid)
return -EAGAIN;

+ pmc_ssram_telemetry->devid = pmc_ssram_telems[pmc_idx].devid;
/*
* Memory barrier is used to ensure the correct read order between
- * device_probed variable and PMC info.
+ * devid variable and base_addr.
*/
smp_rmb();
- if (pmc_idx >= MAX_NUM_PMC)
- return -EINVAL;
-
- if (!pmc_ssram_telems[pmc_idx].devid)
- return -ENODEV;
-
- pmc_ssram_telemetry->devid = pmc_ssram_telems[pmc_idx].devid;
pmc_ssram_telemetry->base_addr = pmc_ssram_telems[pmc_idx].base_addr;
return 0;
}
@@ -209,12 +209,6 @@ static int pmc_ssram_telemetry_probe(struct pci_dev *pcidev, const struct pci_de
ret = -EINVAL;

probe_finish:
- /*
- * Memory barrier is used to ensure the correct write order between PMC info
- * and device_probed variable.
- */
- smp_wmb();
- device_probed = true;
return ret;
}

--
2.43.0