Re: [PATCHv7 3/3] iommu: arm-smmu-impl: Add sdm845 implementation hook

[Bjorn Andersson]

On Fri 20 Sep 01:04 PDT 2019, Sai Prakash Ranjan wrote:

> From: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> 
> Add reset hook for sdm845 based platforms to turn off
> the wait-for-safe sequence.
> 
> Understanding how wait-for-safe logic affects USB and UFS performance
> on MTP845 and DB845 boards:
> 
> Qcom's implementation of arm,mmu-500 adds a WAIT-FOR-SAFE logic
> to address under-performance issues in real-time clients, such as
> Display, and Camera.
> On receiving an invalidation requests, the SMMU forwards SAFE request
> to these clients and waits for SAFE ack signal from real-time clients.
> The SAFE signal from such clients is used to qualify the start of
> invalidation.
> This logic is controlled by chicken bits, one for each - MDP (display),
> IFE0, and IFE1 (camera), that can be accessed only from secure software
> on sdm845.
> 
> This configuration, however, degrades the performance of non-real time
> clients, such as USB, and UFS etc. This happens because, with wait-for-safe
> logic enabled the hardware tries to throttle non-real time clients while
> waiting for SAFE ack signals from real-time clients.
> 
> On mtp845 and db845 devices, with wait-for-safe logic enabled by the
> bootloaders we see degraded performance of USB and UFS when kernel
> enables the smmu stage-1 translations for these clients.
> Turn off this wait-for-safe logic from the kernel gets us back the perf
> of USB and UFS devices until we re-visit this when we start seeing perf
> issues on display/camera on upstream supported SDM845 platforms.
> The bootloaders on these boards implement secure monitor callbacks to
> handle a specific command - QCOM_SCM_SVC_SMMU_PROGRAM with which the
> logic can be toggled.
> 
> There are other boards such as cheza whose bootloaders don't enable this
> logic. Such boards don't implement callbacks to handle the specific SCM
> call so disabling this logic for such boards will be a no-op.
> 
> This change is inspired by the downstream change from Patrick Daly
> to address performance issues with display and camera by handling
> this wait-for-safe within separte io-pagetable ops to do TLB
> maintenance. So a big thanks to him for the change and for all the
> offline discussions.
> 
> Without this change the UFS reads are pretty slow:
> $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=10 conv=sync
> 10+0 records in
> 10+0 records out
> 10485760 bytes (10.0MB) copied, 22.394903 seconds, 457.2KB/s
> real    0m 22.39s
> user    0m 0.00s
> sys     0m 0.01s
> 
> With this change they are back to rock!
> $ time dd if=/dev/sda of=/dev/zero bs=1048576 count=300 conv=sync
> 300+0 records in
> 300+0 records out
> 314572800 bytes (300.0MB) copied, 1.030541 seconds, 291.1MB/s
> real    0m 1.03s
> user    0m 0.00s
> sys     0m 0.54s
> 
> Signed-off-by: Vivek Gautam <vivek.gautam@xxxxxxxxxxxxxx>
> Reviewed-by: Robin Murphy <robin.murphy@xxxxxxx>
> Signed-off-by: Sai Prakash Ranjan <saiprakash.ranjan@xxxxxxxxxxxxxx>

Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>

> ---
>  drivers/iommu/Makefile        |  2 +-
>  drivers/iommu/arm-smmu-impl.c |  5 +++-
>  drivers/iommu/arm-smmu-qcom.c | 51 +++++++++++++++++++++++++++++++++++
>  drivers/iommu/arm-smmu.h      |  3 +++
>  4 files changed, 59 insertions(+), 2 deletions(-)
>  create mode 100644 drivers/iommu/arm-smmu-qcom.c
> 
> diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> index 4f405f926e73..86dadd13b2e6 100644
> --- a/drivers/iommu/Makefile
> +++ b/drivers/iommu/Makefile
> @@ -13,7 +13,7 @@ obj-$(CONFIG_MSM_IOMMU) += msm_iommu.o
>  obj-$(CONFIG_AMD_IOMMU) += amd_iommu.o amd_iommu_init.o amd_iommu_quirks.o
>  obj-$(CONFIG_AMD_IOMMU_DEBUGFS) += amd_iommu_debugfs.o
>  obj-$(CONFIG_AMD_IOMMU_V2) += amd_iommu_v2.o
> -obj-$(CONFIG_ARM_SMMU) += arm-smmu.o arm-smmu-impl.o
> +obj-$(CONFIG_ARM_SMMU) += arm-smmu.o arm-smmu-impl.o arm-smmu-qcom.o
>  obj-$(CONFIG_ARM_SMMU_V3) += arm-smmu-v3.o
>  obj-$(CONFIG_DMAR_TABLE) += dmar.o
>  obj-$(CONFIG_INTEL_IOMMU) += intel-iommu.o intel-pasid.o
> diff --git a/drivers/iommu/arm-smmu-impl.c b/drivers/iommu/arm-smmu-impl.c
> index 5c87a38620c4..b2fe72a8f019 100644
> --- a/drivers/iommu/arm-smmu-impl.c
> +++ b/drivers/iommu/arm-smmu-impl.c
> @@ -109,7 +109,7 @@ static struct arm_smmu_device *cavium_smmu_impl_init(struct arm_smmu_device *smm
>  #define ARM_MMU500_ACR_S2CRB_TLBEN	(1 << 10)
>  #define ARM_MMU500_ACR_SMTNMB_TLBEN	(1 << 8)
>  
> -static int arm_mmu500_reset(struct arm_smmu_device *smmu)
> +int arm_mmu500_reset(struct arm_smmu_device *smmu)
>  {
>  	u32 reg, major;
>  	int i;
> @@ -170,5 +170,8 @@ struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu)
>  				  "calxeda,smmu-secure-config-access"))
>  		smmu->impl = &calxeda_impl;
>  
> +	if (of_device_is_compatible(smmu->dev->of_node, "qcom,sdm845-smmu-500"))
> +		return qcom_smmu_impl_init(smmu);
> +
>  	return smmu;
>  }
> diff --git a/drivers/iommu/arm-smmu-qcom.c b/drivers/iommu/arm-smmu-qcom.c
> new file mode 100644
> index 000000000000..24c071c1d8b0
> --- /dev/null
> +++ b/drivers/iommu/arm-smmu-qcom.c
> @@ -0,0 +1,51 @@
> +// SPDX-License-Identifier: GPL-2.0-only
> +/*
> + * Copyright (c) 2019, The Linux Foundation. All rights reserved.
> + */
> +
> +#include <linux/qcom_scm.h>
> +
> +#include "arm-smmu.h"
> +
> +struct qcom_smmu {
> +	struct arm_smmu_device smmu;
> +};
> +
> +static int qcom_sdm845_smmu500_reset(struct arm_smmu_device *smmu)
> +{
> +	int ret;
> +
> +	arm_mmu500_reset(smmu);
> +
> +	/*
> +	 * To address performance degradation in non-real time clients,
> +	 * such as USB and UFS, turn off wait-for-safe on sdm845 based boards,
> +	 * such as MTP and db845, whose firmwares implement secure monitor
> +	 * call handlers to turn on/off the wait-for-safe logic.
> +	 */
> +	ret = qcom_scm_qsmmu500_wait_safe_toggle(0);
> +	if (ret)
> +		dev_warn(smmu->dev, "Failed to turn off SAFE logic\n");
> +
> +	return ret;
> +}
> +
> +static const struct arm_smmu_impl qcom_smmu_impl = {
> +	.reset = qcom_sdm845_smmu500_reset,
> +};
> +
> +struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu)
> +{
> +	struct qcom_smmu *qsmmu;
> +
> +	qsmmu = devm_kzalloc(smmu->dev, sizeof(*qsmmu), GFP_KERNEL);
> +	if (!qsmmu)
> +		return ERR_PTR(-ENOMEM);
> +
> +	qsmmu->smmu = *smmu;
> +
> +	qsmmu->smmu.impl = &qcom_smmu_impl;
> +	devm_kfree(smmu->dev, smmu);
> +
> +	return &qsmmu->smmu;
> +}
> diff --git a/drivers/iommu/arm-smmu.h b/drivers/iommu/arm-smmu.h
> index b19b6cae9b5e..de99a85e140a 100644
> --- a/drivers/iommu/arm-smmu.h
> +++ b/drivers/iommu/arm-smmu.h
> @@ -398,5 +398,8 @@ static inline void arm_smmu_writeq(struct arm_smmu_device *smmu, int page,
>  	arm_smmu_writeq((s), ARM_SMMU_CB((s), (n)), (o), (v))
>  
>  struct arm_smmu_device *arm_smmu_impl_init(struct arm_smmu_device *smmu);
> +struct arm_smmu_device *qcom_smmu_impl_init(struct arm_smmu_device *smmu);
> +
> +int arm_mmu500_reset(struct arm_smmu_device *smmu);
>  
>  #endif /* _ARM_SMMU_H */
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
>