[PATCH v2] ACPI/IORT: Check node revision for PMCG resources

[Robin Murphy <robin.murphy@arm.com>]

The original version of the IORT PMCG definition had an oversight
wherein there was no way to describe the second register page for an
implementation using the recommended RELOC_CTRS feature. Although the
spec was fixed, and the final patches merged to ACPICA and Linux written
against the new version, it seems that some old firmware based on the
original revision has survived and turned up in the wild.

Add a check for the original PMCG definition, and avoid filling in the
second memory resource with nonsense if so. Otherwise it is likely that
something horrible will happen when the PMCG driver attempts to probe.

Reported-by: Michael Petlan <mpetlan@redhat.com>
Fixes: 24e516049360 ("ACPI/IORT: Add support for PMCG")
Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---

v2: Simpler workaround, since I realised platform_get_resource()
    should happily just skip over a zero-initialised hole in the
    resource array.

 drivers/acpi/arm64/iort.c | 14 +++++++++++---
 1 file changed, 11 insertions(+), 3 deletions(-)

diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
index 175397913be1..7092b94b2aae 100644
--- a/drivers/acpi/arm64/iort.c
+++ b/drivers/acpi/arm64/iort.c
@@ -1371,9 +1371,17 @@ static void __init arm_smmu_v3_pmcg_init_resources(struct resource *res,
 	res[0].start = pmcg->page0_base_address;
 	res[0].end = pmcg->page0_base_address + SZ_4K - 1;
 	res[0].flags = IORESOURCE_MEM;
-	res[1].start = pmcg->page1_base_address;
-	res[1].end = pmcg->page1_base_address + SZ_4K - 1;
-	res[1].flags = IORESOURCE_MEM;
+	/*
+	 * The initial version in DEN0049C lacked a way to describe register
+	 * page 1, which makes it broken for most PMCG implementations; in
+	 * that case, just let the driver fail gracefully if it expects to
+	 * find a second memory resource.
+	 */
+	if (node->revision > 0) {
+		res[1].start = pmcg->page1_base_address;
+		res[1].end = pmcg->page1_base_address + SZ_4K - 1;
+		res[1].flags = IORESOURCE_MEM;
+	}
 
 	if (pmcg->overflow_gsiv)
 		acpi_iort_register_irq(pmcg->overflow_gsiv, "overflow",
-- 
2.28.0.dirty