Re: [PATCH v3 3/4] iommu/arm-smmu: Add support to handle Qcom's wait-for-safe logic

[Vivek Gautam]

On 6/14/2019 9:35 AM, Bjorn Andersson wrote:
> On Wed 12 Jun 00:15 PDT 2019, Vivek Gautam wrote:
>
> > 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 MTP sdm845 devices, with wait-for-safe logic enabled at the boot time
> > 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.
> >
> > Now, different bootloaders with their access control policies allow this
> > register access differently through secure monitor calls -
> > 1) With one we can issue io-read/write secure monitor call (qcom-scm)
> >     to update the register, while,
> > 2) With other, such as one on MTP sdm845 we should use the specific
> >     qcom-scm command to send request to do the complete register
> >     configuration.
> > Adding a separate device tree flag for arm-smmu to identify which
> > firmware configuration of the two mentioned above we use.
> > Not adding code change to allow type-(1) bootloaders to toggle the
> > safe using io-read/write qcom-scm call.
> >
> > 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.
> >
> > 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>
> > ---
> >   drivers/iommu/arm-smmu.c | 16 ++++++++++++++++
> >   1 file changed, 16 insertions(+)
> >
> > diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> > index 0ad086da399c..3c3ad43eda97 100644
> > --- a/drivers/iommu/arm-smmu.c
> > +++ b/drivers/iommu/arm-smmu.c
> > @@ -39,6 +39,7 @@
> >   #include <linux/pci.h>
> >   #include <linux/platform_device.h>
> >   #include <linux/pm_runtime.h>
> > +#include <linux/qcom_scm.h>
> >   #include <linux/slab.h>
> >   #include <linux/spinlock.h>
> >   
> > @@ -177,6 +178,7 @@ struct arm_smmu_device {
> >   	u32				features;
> >   
> >   #define ARM_SMMU_OPT_SECURE_CFG_ACCESS (1 << 0)
> > +#define ARM_SMMU_OPT_QCOM_FW_IMPL_SAFE_ERRATA (1 << 1)
> >   	u32				options;
> >   	enum arm_smmu_arch_version	version;
> >   	enum arm_smmu_implementation	model;
> > @@ -262,6 +264,7 @@ static bool using_legacy_binding, using_generic_binding;
> >   
> >   static struct arm_smmu_option_prop arm_smmu_options[] = {
> >   	{ ARM_SMMU_OPT_SECURE_CFG_ACCESS, "calxeda,smmu-secure-config-access" },
> > +	{ ARM_SMMU_OPT_QCOM_FW_IMPL_SAFE_ERRATA, "qcom,smmu-500-fw-impl-safe-errata" },
> This should be added to the DT binding as well.

Ah right. I missed that. Will add this and respin unless Robin and Will 
have concerns with this change.

> >   	{ 0, NULL},
> >   };
> >   
> > @@ -2292,6 +2295,19 @@ static int arm_smmu_device_probe(struct platform_device *pdev)
> >   	arm_smmu_device_reset(smmu);
> >   	arm_smmu_test_smr_masks(smmu);
> >   
> > +	/*
> > +	 * To address performance degradation in non-real time clients,
> > +	 * such as USB and UFS, turn off wait-for-safe on sdm845 platforms,
> > +	 * such as MTP, whose firmwares implement corresponding secure monitor
> > +	 * call handlers.
> > +	 */
> > +	if (of_device_is_compatible(smmu->dev->of_node, "qcom,sdm845-smmu-500") &&
> > +	    smmu->options & ARM_SMMU_OPT_QCOM_FW_IMPL_SAFE_ERRATA) {
> > +		err = qcom_scm_qsmmu500_wait_safe_toggle(0);
> > +		if (err)
> > +			dev_warn(dev, "Failed to turn off SAFE logic\n");
> > +	}
> > +
> This looks good, I presume at some point we can profile things and
> review if it's worth toggling this on the fly, but given that this is
> conditioned on smmu->options that should be an implementation detail..
>
> Reviewed-by: Bjorn Andersson <bjorn.andersson@xxxxxxxxxx>

Thanks Bjorn.

Best regards
Vivek

> Regards,
> Bjorn
>
> >   	/*
> >   	 * We want to avoid touching dev->power.lock in fastpaths unless
> >   	 * it's really going to do something useful - pm_runtime_enabled()
> > --
> > QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> > of Code Aurora Forum, hosted by The Linux Foundation