[PATCH v3 09/10] iommu/arm-smmu: Get associated RMR info and install bypass SMR

[Shameerali Kolothum Thodi]

> -----Original Message-----
> From: Steven Price [mailto:steven.price at arm.com]
> Sent: 06 May 2021 16:17
> To: Shameerali Kolothum Thodi <shameerali.kolothum.thodi at huawei.com>;
> linux-arm-kernel at lists.infradead.org; linux-acpi at vger.kernel.org;
> iommu at lists.linux-foundation.org
> Cc: Linuxarm <linuxarm at huawei.com>; lorenzo.pieralisi at arm.com;
> joro at 8bytes.org; robin.murphy at arm.com; wanghuiqiang
> <wanghuiqiang at huawei.com>; Guohanjun (Hanjun Guo)
> <guohanjun at huawei.com>; Sami.Mujawar at arm.com; jon at solid-run.com;
> eric.auger at redhat.com
> Subject: Re: [PATCH v3 09/10] iommu/arm-smmu: Get associated RMR info
> and install bypass SMR
> 
> On 20/04/2021 09:27, Shameer Kolothum wrote:
> > From: Jon Nettleton <jon at solid-run.com>
> >
> > Check if there is any RMR info associated with the devices behind
> > the SMMU and if any, install bypass SMRs for them. This is to
> > keep any ongoing traffic associated with these devices alive
> > when we enable/reset SMMU during probe().
> >
> > Signed-off-by: Jon Nettleton <jon at solid-run.com>
> > Signed-off-by: Shameer Kolothum
> <shameerali.kolothum.thodi at huawei.com>
> > ---
> >   drivers/iommu/arm/arm-smmu/arm-smmu.c | 42
> +++++++++++++++++++++++++++
> >   drivers/iommu/arm/arm-smmu/arm-smmu.h |  2 ++
> >   2 files changed, 44 insertions(+)
> >
> > diff --git a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > index d8c6bfde6a61..4d2f91626d87 100644
> > --- a/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > +++ b/drivers/iommu/arm/arm-smmu/arm-smmu.c
> > @@ -2102,6 +2102,43 @@ err_reset_platform_ops: __maybe_unused;
> >   	return err;
> >   }
> >
> > +static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device
> *smmu)
> > +{
> > +	struct iommu_rmr *e;
> > +	int i, cnt = 0;
> > +	u32 smr;
> > +
> > +	for (i = 0; i < smmu->num_mapping_groups; i++) {
> > +		smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
> > +		if (!FIELD_GET(ARM_SMMU_SMR_VALID, smr))
> > +			continue;
> > +
> > +		list_for_each_entry(e, &smmu->rmr_list, list) {
> > +			if (FIELD_GET(ARM_SMMU_SMR_ID, smr) != e->sid)
> > +				continue;
> > +
> > +			smmu->smrs[i].id = FIELD_GET(ARM_SMMU_SMR_ID, smr);
> > +			smmu->smrs[i].mask = FIELD_GET(ARM_SMMU_SMR_MASK,
> smr);
> > +			smmu->smrs[i].valid = true;
> > +
> > +			smmu->s2crs[i].type = S2CR_TYPE_BYPASS;
> > +			smmu->s2crs[i].privcfg = S2CR_PRIVCFG_DEFAULT;
> > +			smmu->s2crs[i].cbndx = 0xff;
> > +
> > +			cnt++;
> > +		}
> > +	}
> 
> If I understand this correctly - this is looking at the current
> (hardware) configuration of the SMMU and attempting to preserve any
> bypass SMRs. However from what I can tell it suffers from the following
> two problems:
> 
>   (a) Only the ID of the SMR is being checked, not the MASK. So if the
> firmware has setup an SMR matching a number of streams this will break.
> 
>   (b) The SMMU might not be enabled at all (CLIENTPD==1) or bypass
> enabled for unmatched streams (USFCFG==0).
> 
> Certainly in my test setup case (b) applies and so this doesn't work.
> Perhaps something like the below would work better? (It works in the
> case of the SMMU not enabled - I've not tested case (a)).

Thanks Steve for taking a look and testing this on SMMUv2. My knowledge
on SMMUv2 is limited an don't have a setup to verify this. After reading
the code, agree that the current implementation addresses the hardware
configuration only and breaks all the scenarios explained above.

I will include the below snippet in next respin if that works.

Hi Jon,

Could you please take a look and see the below changes works for
you too?

Thanks,
Shameer

> ----8<----
> static void arm_smmu_rmr_install_bypass_smr(struct arm_smmu_device
> *smmu)
> {
> 	struct iommu_rmr *e;
> 	int i, cnt = 0;
> 	u32 smr;
> 	u32 reg;
> 
> 	reg = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_sCR0);
> 
> 	if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg &
> ARM_SMMU_sCR0_CLIENTPD)) {
> 		/*
> 		 * SMMU is already enabled and disallowing bypass, so preserve
> 		 * the existing SMRs
> 		 */
> 		for (i = 0; i < smmu->num_mapping_groups; i++) {
> 			smr = arm_smmu_gr0_read(smmu, ARM_SMMU_GR0_SMR(i));
> 			if (!FIELD_GET(ARM_SMMU_SMR_VALID, smr))
> 				continue;
> 			smmu->smrs[i].id = FIELD_GET(ARM_SMMU_SMR_ID, smr);
> 			smmu->smrs[i].mask = FIELD_GET(ARM_SMMU_SMR_MASK,
> smr);
> 			smmu->smrs[i].valid = true;
> 		}
> 	}
> 
> 	list_for_each_entry(e, &smmu->rmr_list, list) {
> 		u32 sid = e->sid;
> 
> 		i = arm_smmu_find_sme(smmu, sid, ~0);
> 		if (i < 0)
> 			continue;
> 		if (smmu->s2crs[i].count == 0) {
> 			smmu->smrs[i].id = sid;
> 			smmu->smrs[i].mask = ~0;
> 			smmu->smrs[i].valid = true;
> 		}
> 		smmu->s2crs[i].count++;
> 		smmu->s2crs[i].type = S2CR_TYPE_BYPASS;
> 		smmu->s2crs[i].privcfg = S2CR_PRIVCFG_DEFAULT;
> 		smmu->s2crs[i].cbndx = 0xff;
> 
> 		cnt++;
> 	}
> 
> 	if ((reg & ARM_SMMU_sCR0_USFCFG) && !(reg &
> ARM_SMMU_sCR0_CLIENTPD)) {
> 		/* Remove the valid bit for unused SMRs */
> 		for (i = 0; i < smmu->num_mapping_groups; i++) {
> 			if (smmu->s2crs[i].count == 0)
> 				smmu->smrs[i].valid = false;
> 		}
> 	}
> 
> 	dev_notice(smmu->dev, "\tpreserved %d boot mapping%s\n", cnt,
> 		   cnt == 1 ? "" : "s");
> }