[PATCH 15/22] ARM: mmu64: allow asserting last level page in __find_pte

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

We do not ever call __find_pte with a NULL level argument.
ARM32 code has a find_pte function that only returns PTEs for 4K pages
and NULL on PMDs which is later checked to trigger a panic.

In preparation for providing the same API in both ARM32 and ARM64,
let's have the ARM64 panic too if level is not specified and document
the semantics of the function.

No functional change.

Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 arch/arm/cpu/mmu_64.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/arch/arm/cpu/mmu_64.c b/arch/arm/cpu/mmu_64.c
index cdfbf081d51f..15b809808153 100644
--- a/arch/arm/cpu/mmu_64.c
+++ b/arch/arm/cpu/mmu_64.c
@@ -95,6 +95,21 @@ static uint64_t *alloc_pte(void)
 }
 #endif
 
+/**
+ * __find_pte - Find page table entry
+ * @ttb: Translation Table Base
+ * @addr: Virtual address to lookup
+ * @level: used to store the level at which the page table walk ended.
+ *         if NULL, asserts that the smallest page was found
+ *
+ * This function walks the page table from the top down and finds the page
+ * table entry associated with the supplied virtual address.
+ * The level at which a page was found is saved into *level.
+ * if the level is NULL, a last level page must be found or the function
+ * panics.
+ *
+ * Returns a pointer to the page table entry
+ */
 static uint64_t *__find_pte(uint64_t *ttb, uint64_t addr, int *level)
 {
 	uint64_t *pte = ttb;
@@ -113,6 +128,8 @@ static uint64_t *__find_pte(uint64_t *ttb, uint64_t addr, int *level)
 			pte = (uint64_t *)(*pte & XLAT_ADDR_MASK);
 	}
 
+	if (!level && i != 3)
+		panic("Got level %d page table entry, where level 3 expected\n", i);
 	if (level)
 		*level = i;
 	return pte;
-- 
2.39.5