[PATCH] iommu/arm-smmu-qcom: Fix fastrpc compatible string in ACTLR client match table

[bibek . patro]

From: Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>

The qcom_smmu_actlr_client_of_match table contained "qcom,fastrpc" as
the compatible string for applying ACTLR prefetch settings to FastRPC
devices. However, "qcom,fastrpc" is the compatible string for the parent
rpmsg channel node, which is not an IOMMU client — it carries no
"iommus" property in the device tree and is never attached to an SMMU
context bank.

The actual IOMMU clients are the compute context bank (CB) child nodes,
which use the compatible string "qcom,fastrpc-compute-cb". These nodes
carry the "iommus" property and are probed by fastrpc_cb_driver via
fastrpc_cb_probe(), which sets up the DMA mask and IOMMU mappings for
each FastRPC session. The device tree structure is:

  fastrpc {
      compatible = "qcom,fastrpc";        /* rpmsg channel, no iommus */
      ...
      compute-cb@3 {
          compatible = "qcom,fastrpc-compute-cb";
          iommus = <&apps_smmu 0x1823 0x0>;  /* actual IOMMU client */
      };
  };

Since qcom_smmu_set_actlr_dev() calls of_match_device() against the
device being attached to the SMMU context bank, the "qcom,fastrpc"
entry was never matching any device. As a result, the ACTLR prefetch
settings (PREFETCH_DEEP | CPRE | CMTLB) were silently never applied
for FastRPC compute context banks.

Fix this by replacing "qcom,fastrpc" with "qcom,fastrpc-compute-cb"
in the match table so that the ACTLR settings are correctly applied
to the compute CB devices that are the true IOMMU clients.

Assisted-by: Anthropic:claude-4-6-sonnet
Fixes: 3e35c3e725de ("iommu/arm-smmu: Add ACTLR data and support for qcom_smmu_500")
Signed-off-by: Bibek Kumar Patro <bibek.patro@xxxxxxxxxxxxxxxx>
---

While there is an ongoing discussion [1] on how to differentiate ACTLR
prefetch settings between compute DSP and audio DSP fastrpc devices, it
is necessary to first fix the compatible string to "qcom,fastrpc-compute-cb".
Both compute DSP and audio DSP fastrpc nodes use this compatible string,
so both will receive the ACTLR settings after this fix. However, for
audio DSP devices the effect remains the same as the current
state since they do not actively use prefetch — the write is effectively
a NOP for them. The fix is meaningful for compute DSP devices, which
actively use prefetch and were previously being silently skipped.

[1]: https://lore.kernel.org/all/9b4c895a-c822-40e6-bb92-8fdcd09c82d3@xxxxxxxxxxxxxxxx/

 drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
index edd41b5a3b6a..2d006049dd61 100644
--- a/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
+++ b/drivers/iommu/arm/arm-smmu/arm-smmu-qcom.c
@@ -39,7 +39,7 @@ static const struct of_device_id qcom_smmu_actlr_client_of_match[] = {
 			.data = (const void *) (PREFETCH_DEEP | CPRE | CMTLB) },
 	{ .compatible = "qcom,adreno-smmu",
 			.data = (const void *) (PREFETCH_DEEP | CPRE | CMTLB) },
-	{ .compatible = "qcom,fastrpc",
+	{ .compatible = "qcom,fastrpc-compute-cb",
 			.data = (const void *) (PREFETCH_DEEP | CPRE | CMTLB) },
 	{ .compatible = "qcom,qcm2290-mdss",
 			.data = (const void *) (PREFETCH_SHALLOW | CPRE | CMTLB) },
--
2.34.1