-----Original Message-----
From: Robin Murphy [mailto:robin.murphy@arm.com]
Sent: 14 June 2021 11:23
To: Shameerali Kolothum Thodi <redacted>;
linux-arm-kernel@lists.infradead.org; linux-acpi@vger.kernel.org;
iommu@lists.linux-foundation.org
Cc: Linuxarm <redacted>; lorenzo.pieralisi@arm.com;
joro@8bytes.org; wanghuiqiang [off-list ref]; Guohanjun
(Hanjun Guo) [off-list ref]; steven.price@arm.com;
Sami.Mujawar@arm.com; jon@solid-run.com; eric.auger@redhat.com;
yangyicong [off-list ref]
Subject: Re: [PATCH v5 5/8] iommu/arm-smmu-v3: Add bypass flag
to arm_smmu_write_strtab_ent()

On 2021-05-24 12:02, Shameer Kolothum wrote:

quoted

By default, disable_bypass is set and any dev without an iommu domain
installs STE with CFG_ABORT during arm_smmu_init_bypass_stes().

Introduce

quoted

a "bypass" flag to arm_smmu_write_strtab_ent() so that we can force it to
install CFG_BYPASS STE for specific SIDs. This will be useful in follow
up patch to install bypass for IORT RMR SIDs.

Signed-off-by: Shameer Kolothum

[off-list ref]

quoted

---
  drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c | 8 ++++----
  1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

quoted

index 754bad6092c1..f9195b740f48 100644

--- a/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c
+++ b/drivers/iommu/arm/arm-smmu-v3/arm-smmu-v3.c

@@ -1174,7 +1174,7 @@ static void arm_smmu_sync_ste_for_sid(struct

arm_smmu_device *smmu, u32 sid)

quoted

  }

  static void arm_smmu_write_strtab_ent(struct arm_smmu_master

*master, u32 sid,

quoted

-				      __le64 *dst)
+				      __le64 *dst, bool bypass)
  {
  	/*
  	 * This is hideously complicated, but we only really care about

@@ -1245,7 +1245,7 @@ static void arm_smmu_write_strtab_ent(struct

arm_smmu_master *master, u32 sid,

quoted

  	/* Bypass/fault */
  	if (!smmu_domain || !(s1_cfg || s2_cfg)) {
-		if (!smmu_domain && disable_bypass)
+		if (!smmu_domain && disable_bypass && !bypass)

Umm...

quoted

  			val |= FIELD_PREP(STRTAB_STE_0_CFG,

STRTAB_STE_0_CFG_ABORT);

quoted

  		else
  			val |= FIELD_PREP(STRTAB_STE_0_CFG,

STRTAB_STE_0_CFG_BYPASS);

quoted

@@ -1320,7 +1320,7 @@ static void arm_smmu_init_bypass_stes(__le64

*strtab, unsigned int nent)

quoted

  	unsigned int i;

  	for (i = 0; i < nent; ++i) {
-		arm_smmu_write_strtab_ent(NULL, -1, strtab);
+		arm_smmu_write_strtab_ent(NULL, -1, strtab, false);

...and in particular, an operation named "init_bypass_stes" passing
bypass=false is just breaking my brain. Can we pull the logic for
default bypass/fault out to here as part of the refactoring so that it
actually makes sense?

Agree, it is confusing. Will add the default bypass/fault logic here.

Thanks,
Shameer

Robin.

quoted

  		strtab += STRTAB_STE_DWORDS;
  	}
  }

@@ -2097,7 +2097,7 @@ static void arm_smmu_install_ste_for_dev(struct

arm_smmu_master *master)

quoted

  		if (j < i)
  			continue;

-		arm_smmu_write_strtab_ent(master, sid, step);
+		arm_smmu_write_strtab_ent(master, sid, step, false);
  	}
  }

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