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

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Message-ID: <d3540512-09c7-0fa5-2b35-6f1112a575a9@arm.com>
Date:   Fri, 3 Jul 2020 09:24:24 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Tomasz Nowicki <tn@...ihalf.com>, will@...nel.org, joro@...tes.org,
        gregory.clement@...tlin.com, robh+dt@...nel.org, hannah@...vell.com
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        devicetree@...r.kernel.org, catalin.marinas@....com,
        nadavh@...vell.com, linux-arm-kernel@...ts.infradead.org,
        mw@...ihalf.com
Subject: Re: [PATCH v3 1/4] iommu/arm-smmu: Add SMMU ID2 register fixup hook

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;
  }