[PATCH] Revert "Revert "Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()"""

[Douglas Anderson]

This reverts commit 7bd6680b47fa4cd53ee1047693c09825e212a6f5.

When booting a sc7180-trogdor based device on mainline, I see errors
that look like this:

 qcom_scm firmware:scm: Assign memory protection call failed -22
 qcom_rmtfs_mem 94600000.memory: assign memory failed
 qcom_rmtfs_mem: probe of 94600000.memory failed with error -22

The device still boots OK, but WiFi doesn't work.

The failure only seems to happen when
CONFIG_INIT_ON_ALLOC_DEFAULT_ON=y. When I don't have that set then
everything is peachy. Presumably something about the extra
initialization disagrees with the change to drop cache invalidation.

Fixes: 7bd6680b47fa ("Revert "Revert "arm64: dma: Drop cache invalidation from arch_dma_prep_coherent()""")
Signed-off-by: Douglas Anderson <dianders@xxxxxxxxxxxx>
---

 arch/arm64/mm/dma-mapping.c | 17 ++++++++++++++++-
 1 file changed, 16 insertions(+), 1 deletion(-)

diff --git a/arch/arm64/mm/dma-mapping.c b/arch/arm64/mm/dma-mapping.c
index 3cb101e8cb29..5240f6acad64 100644
--- a/arch/arm64/mm/dma-mapping.c
+++ b/arch/arm64/mm/dma-mapping.c
@@ -36,7 +36,22 @@ void arch_dma_prep_coherent(struct page *page, size_t size)
 {
 	unsigned long start = (unsigned long)page_address(page);
 
-	dcache_clean_poc(start, start + size);
+	/*
+	 * The architecture only requires a clean to the PoC here in order to
+	 * meet the requirements of the DMA API. However, some vendors (i.e.
+	 * Qualcomm) abuse the DMA API for transferring buffers from the
+	 * non-secure to the secure world, resetting the system if a non-secure
+	 * access shows up after the buffer has been transferred:
+	 *
+	 * https://lore.kernel.org/r/20221114110329.68413-1-manivannan.sadhasivam@xxxxxxxxxx
+	 *
+	 * Using clean+invalidate appears to make this issue less likely, but
+	 * the drivers themselves still need fixing as the CPU could issue a
+	 * speculative read from the buffer via the linear mapping irrespective
+	 * of the cache maintenance we use. Once the drivers are fixed, we can
+	 * relax this to a clean operation.
+	 */
+	dcache_clean_inval_poc(start, start + size);
 }
 
 #ifdef CONFIG_IOMMU_DMA
-- 
2.41.0.162.gfafddb0af9-goog