Re: [PATCH v3 1/4] iommu/arm-smmu: Add SMMU ID2 register fixup hook

[Robin Murphy]

On 2020-07-02 21:16, Tomasz Nowicki wrote:
> We already have 'cfg_probe' hook which meant to override and apply
> workarounds while probing ID registers. However, 'cfg_probe' is called
> at the very end and therefore for some cases fixing up things becomes complex
> or requires exporting of SMMU driver structures. Hence, seems it is better and
> cleaner to do ID fixup right away. In preparation for adding Marvell
> errata add an extra ID2 fixup hook.

Hmm, the intent of ->cfg_probe was very much to give impl a chance to 
adjust the detected features before we start consuming them, with this 
exact case in mind. Since the Cavium quirk isn't actually doing that - 
it just needs to run *anywhere* in the whole probe process - I'm under 
no illusion that I put the hook in exactly the right place first time 
around ;)

The diff below should be more on the mark...

Robin.

----->8-----
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
index 243bc4cb2705..884ffca5b1eb 100644
--- a/drivers/iommu/arm-smmu.c
+++ b/drivers/iommu/arm-smmu.c
@@ -1891,6 +1891,9 @@ static int arm_smmu_device_cfg_probe(struct 
arm_smmu_device *smmu)
 			smmu->features |= ARM_SMMU_FEAT_FMT_AARCH64_64K;
 	}

+	if (smmu->impl && smmu->impl->cfg_probe)
+		return smmu->impl->cfg_probe(smmu);
+
 	/* Now we've corralled the various formats, what'll it do? */
 	if (smmu->features & ARM_SMMU_FEAT_FMT_AARCH32_S)
 		smmu->pgsize_bitmap |= SZ_4K | SZ_64K | SZ_1M | SZ_16M;
@@ -1909,7 +1912,6 @@ static int arm_smmu_device_cfg_probe(struct 
arm_smmu_device *smmu)
 	dev_notice(smmu->dev, "\tSupported page sizes: 0x%08lx\n",
 		   smmu->pgsize_bitmap);

-
 	if (smmu->features & ARM_SMMU_FEAT_TRANS_S1)
 		dev_notice(smmu->dev, "\tStage-1: %lu-bit VA -> %lu-bit IPA\n",
 			   smmu->va_size, smmu->ipa_size);
@@ -1918,9 +1920,6 @@ static int arm_smmu_device_cfg_probe(struct 
arm_smmu_device *smmu)
 		dev_notice(smmu->dev, "\tStage-2: %lu-bit IPA -> %lu-bit PA\n",
 			   smmu->ipa_size, smmu->pa_size);

-	if (smmu->impl && smmu->impl->cfg_probe)
-		return smmu->impl->cfg_probe(smmu);
-
 	return 0;
 }