Re: [PATCH v2 2/5] iommu/arm-smmu: Emulate bypass by using context banks
From: Jordan Crouse <hidden>
Date: 2020-07-20 16:36:56
Also in:
linux-arm-msm, linux-iommu, lkml
On Mon, Jul 20, 2020 at 09:58:42AM +0100, Will Deacon wrote:
On Thu, Jul 16, 2020 at 05:16:16PM -0700, Bjorn Andersson wrote:quoted
Some firmware found on various Qualcomm platforms traps writes to S2CR of type BYPASS and writes FAULT into the register. This prevents us from marking the streams for the display controller as BYPASS to allow continued scanout of the screen through the initialization of the ARM SMMU. This adds a Qualcomm specific cfg_probe function, which probes the behavior of the S2CR registers and if found faulty enables the related quirk. Based on this quirk context banks are allocated for IDENTITY domains as well, but with ARM_SMMU_SCTLR_M omitted. The result is valid stream mappings, without translation. Tested-by: John Stultz <redacted> Tested-by: Vinod Koul <vkoul@kernel.org> Signed-off-by: Bjorn Andersson <redacted> --- Changes since v1: - Picked up tested-by drivers/iommu/arm-smmu-qcom.c | 21 +++++++++++++++++++++ drivers/iommu/arm-smmu.c | 14 ++++++++++++-- drivers/iommu/arm-smmu.h | 3 +++ 3 files changed, 36 insertions(+), 2 deletions(-)[...]quoted
diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c index fb85e716ae9a..5d5fe6741ed4 100644 --- a/drivers/iommu/arm-smmu.c +++ b/drivers/iommu/arm-smmu.c@@ -654,7 +654,9 @@ static void arm_smmu_write_context_bank(struct arm_smmu_device *smmu, int idx) /* SCTLR */ reg = ARM_SMMU_SCTLR_CFIE | ARM_SMMU_SCTLR_CFRE | ARM_SMMU_SCTLR_AFE | - ARM_SMMU_SCTLR_TRE | ARM_SMMU_SCTLR_M; + ARM_SMMU_SCTLR_TRE; + if (cfg->m) + reg |= ARM_SMMU_SCTLR_M; if (stage1) reg |= ARM_SMMU_SCTLR_S1_ASIDPNE; if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN))@@ -678,7 +680,11 @@ static int arm_smmu_init_domain_context(struct iommu_domain *domain, if (smmu_domain->smmu) goto out_unlock; - if (domain->type == IOMMU_DOMAIN_IDENTITY) { + /* + * Nothing to do for IDENTITY domains,unless disabled context banks are + * used to emulate bypass mappings on Qualcomm platforms. + */ + if (domain->type == IOMMU_DOMAIN_IDENTITY && !smmu->qcom_bypass_quirk) {Given that the other thread [1] with Jordan (why haven't you cc'd him?! -- adding him now) has identified the need for a callback to allocate the context bank, why don't we use the same sort of idea here? If the impl provides a CB allocator function, call it irrespective of the domain type. If it allocates a domain even for an identity domain, then we can install if with SCTLR.M clear.
Here is what I have so far for the context bank allocator. I think its a good start, but it still feels a bit half baked, so comments definitely welcome. https://lists.linuxfoundation.org/pipermail/iommu/2020-July/046754.html https://lists.linuxfoundation.org/pipermail/iommu/2020-July/046752.html
Will [1] https://lore.kernel.org/r/20200716151625.GA14526@jcrouse1-lnx.qualcomm.com (local)
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