Re: [PATCH v2 11/11] iommu/tegra-smmu: Use a DMA API default domain per swgroup

[Mikko Perttunen <mperttunen@nvidia.com>]

On Wednesday, October 21, 2026 12:30 AM Robin Murphy wrote:
> On 16/10/2026 7:46 am, Mikko Perttunen wrote:
> > Everything is now in place for the Tegra SMMU to give devices a real
> > IOMMU_DOMAIN_DMA default domain.
> > 
> > Some device drivers still rely on explicit domains (and being able to
> > detach a legacy ARM DMA domain if any), so DMA default domains are
> > enabled on a per-swgroup basis via a use_dma_api flag. As drivers are
> > converted to DMA API usage we can eventually get rid of this. Initially
> > the flag is enabled for TegraDRM and Host1x devices.
> > 
> > On multi_v7_defconfig (where CONFIG_ARM_DMA_USE_IOMMU was always
> > enabled), this will fix TegraDRM probing with certain probe orderings
> > where the legacy implementation's lack of support for multiple devices
> > in one IOMMU group would cause breakage.
> > 
> > On tegra_defconfig, as this now enables CONFIG_ARM_DMA_USE_IOMMU, all
> > devices move to either the legacy ARM DMA path or the new one. This
> > should in principle not cause issues as the drivers would already have
> > been verified on multi_v7_defconfig.
> > 
> > Also set .release_domain to the identity domain to ensure the AS is
> > released appropriately now that the domain can be non-static.
> > 
> > Signed-off-by: Mikko Perttunen <mperttunen@nvidia.com>
> > ---
> >   drivers/iommu/Kconfig           |  1 +
> >   drivers/iommu/tegra-smmu.c      | 59 ++++++++++++++++++++++++++++++++++++++---
> >   drivers/memory/tegra/tegra114.c | 13 +++++----
> >   drivers/memory/tegra/tegra124.c | 10 ++++---
> >   drivers/memory/tegra/tegra30.c  | 16 ++++++-----
> >   include/soc/tegra/mc.h          |  7 +++++
> >   6 files changed, 87 insertions(+), 19 deletions(-)
> > 
> > diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
> > index 6e07bd69467a..817e84e0e6ab 100644
> > --- a/drivers/iommu/Kconfig
> > +++ b/drivers/iommu/Kconfig
> > @@ -252,6 +252,7 @@ config TEGRA_IOMMU_SMMU
> >   	depends on TEGRA_AHB
> >   	depends on TEGRA_MC
> >   	select IOMMU_API
> > +	select ARM_DMA_USE_IOMMU if ARM
> >   	help
> >   	  This driver supports the IOMMU hardware (SMMU) found on NVIDIA Tegra
> >   	  SoCs (Tegra30 up to Tegra210).
> > diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
> > index 6779528a9e7c..1c1910f25553 100644
> > --- a/drivers/iommu/tegra-smmu.c
> > +++ b/drivers/iommu/tegra-smmu.c
> > @@ -994,16 +994,31 @@ static int tegra_smmu_of_xlate(struct device *dev,
> >   
> >   static int tegra_smmu_def_domain_type(struct device *dev)
> >   {
> > +	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
> > +	struct tegra_smmu *smmu = dev_iommu_priv_get(dev);
> > +	unsigned int i;
> > +
> > +	if (!fwspec || !smmu)
> > +		return IOMMU_DOMAIN_IDENTITY;
> 
> Dead code - by this point tegra_smmu_probe_device() has already run (and 
> we've literally reached this call via dev_iommu_ops(dev)) so the device 
> is definitely valid.
> 
> > +
> >   	/*
> > -	 * FIXME: For now we want to run all translation in IDENTITY mode, due
> > -	 * to some device quirks. Better would be to just quirk the troubled
> > -	 * devices.
> > +	 * Only clients known to work with the DMA API get a DMA default domain.
> > +	 * The rest keep running in identity mode.
> >   	 */
> > -	return IOMMU_DOMAIN_IDENTITY;
> > +	for (i = 0; i < fwspec->num_ids; i++) {
> > +		const struct tegra_smmu_swgroup *group;
> > +
> > +		group = tegra_smmu_find_swgroup(smmu, fwspec->ids[i]);
> > +		if (!group || !group->use_dma_api)
> 
> Similarly, dev->iommu_group is already assigned with whatever valid 
> group tegra_smmu_device_group() returned, so you could perhaps just do a 
> single iteration over smmu->groups for the lookup.

Yeah, this was way overcomplicated. I've rewritten the function to 
directly pass the fwspec ID to tegra_smmu_find_swgroup - much simpler.

Thanks!
Mikko

> 
> Thanks,
> Robin.
> 
> > +			return IOMMU_DOMAIN_IDENTITY;
> > +	}
> > +
> > +	return IOMMU_DOMAIN_DMA;
> >   }
> >   
> >   static const struct iommu_ops tegra_smmu_ops = {
> >   	.identity_domain = &tegra_smmu_identity_domain,
> > +	.release_domain = &tegra_smmu_identity_domain,
> >   	.def_domain_type = &tegra_smmu_def_domain_type,
> >   	.domain_alloc_paging = tegra_smmu_domain_alloc_paging,
> >   	.probe_device = tegra_smmu_probe_device,
> > @@ -1108,6 +1123,40 @@ static void tegra_smmu_debugfs_exit(struct tegra_smmu *smmu)
> >   	debugfs_remove_recursive(smmu->debugfs);
> >   }
> >   
> > +/*
> > + * The default domain type is a property of the IOMMU group, so all swgroups in
> > + * one group must agree on use_dma_api. Otherwise the core sees conflicting
> > + * def_domain_type and falls back to identity for the whole group.
> > + */
> > +static void tegra_smmu_check_groups(struct tegra_smmu *smmu)
> > +{
> > +	const struct tegra_smmu_soc *soc = smmu->soc;
> > +	unsigned int i, j;
> > +
> > +	for (i = 0; i < soc->num_groups; i++) {
> > +		const struct tegra_smmu_group_soc *group = &soc->groups[i];
> > +		int dma_api = -1;
> > +
> > +		for (j = 0; j < group->num_swgroups; j++) {
> > +			const struct tegra_smmu_swgroup *swgrp;
> > +
> > +			swgrp = tegra_smmu_find_swgroup(smmu,
> > +							group->swgroups[j]);
> > +			if (!swgrp)
> > +				continue;
> > +
> > +			if (dma_api < 0)
> > +				dma_api = swgrp->use_dma_api;
> > +			else if (swgrp->use_dma_api != !!dma_api)
> > +				break;
> > +		}
> > +
> > +		WARN(j < group->num_swgroups,
> > +		     "SMMU group %s mixes DMA API and identity swgroups\n",
> > +		     group->name);
> > +	}
> > +}
> > +
> >   struct tegra_smmu *tegra_smmu_probe(struct device *dev,
> >   				    const struct tegra_smmu_soc *soc,
> >   				    struct tegra_mc *mc)
> > @@ -1142,6 +1191,8 @@ struct tegra_smmu *tegra_smmu_probe(struct device *dev,
> >   	smmu->dev = dev;
> >   	smmu->mc = mc;
> >   
> > +	tegra_smmu_check_groups(smmu);
> > +
> >   	smmu->pfn_mask =
> >   		BIT_MASK(mc->soc->num_address_bits - SMMU_PTE_SHIFT) - 1;
> >   	dev_dbg(dev, "address bits: %u, PFN mask: %#lx\n",
> > diff --git a/drivers/memory/tegra/tegra114.c b/drivers/memory/tegra/tegra114.c
> > index 2883c4f91144..024c63bdd480 100644
> > --- a/drivers/memory/tegra/tegra114.c
> > +++ b/drivers/memory/tegra/tegra114.c
> > @@ -1029,15 +1029,18 @@ static const struct tegra_mc_client tegra114_mc_clients[] = {
> >   
> >   static const struct tegra_smmu_swgroup tegra114_swgroups[] = {
> >   	{ .name = "dc",        .swgroup = TEGRA_SWGROUP_DC,        .reg = 0x240,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "dcb",       .swgroup = TEGRA_SWGROUP_DCB,       .reg = 0x244,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "epp",       .swgroup = TEGRA_SWGROUP_EPP,       .reg = 0x248 },
> > -	{ .name = "g2",        .swgroup = TEGRA_SWGROUP_G2,        .reg = 0x24c },
> > +	{ .name = "g2",        .swgroup = TEGRA_SWGROUP_G2,        .reg = 0x24c,
> > +	  .use_dma_api = true },
> >   	{ .name = "avpc",      .swgroup = TEGRA_SWGROUP_AVPC,      .reg = 0x23c },
> > -	{ .name = "nv",        .swgroup = TEGRA_SWGROUP_NV,        .reg = 0x268 },
> > +	{ .name = "nv",        .swgroup = TEGRA_SWGROUP_NV,        .reg = 0x268,
> > +	  .use_dma_api = true },
> >   	{ .name = "hda",       .swgroup = TEGRA_SWGROUP_HDA,       .reg = 0x254 },
> > -	{ .name = "hc",        .swgroup = TEGRA_SWGROUP_HC,        .reg = 0x250 },
> > +	{ .name = "hc",        .swgroup = TEGRA_SWGROUP_HC,        .reg = 0x250,
> > +	  .use_dma_api = true },
> >   	{ .name = "msenc",     .swgroup = TEGRA_SWGROUP_MSENC,     .reg = 0x264 },
> >   	{ .name = "ppcs",      .swgroup = TEGRA_SWGROUP_PPCS,      .reg = 0x270 },
> >   	{ .name = "vde",       .swgroup = TEGRA_SWGROUP_VDE,       .reg = 0x27c },
> > diff --git a/drivers/memory/tegra/tegra124.c b/drivers/memory/tegra/tegra124.c
> > index a38fbf2baf6c..17068aaf163f 100644
> > --- a/drivers/memory/tegra/tegra124.c
> > +++ b/drivers/memory/tegra/tegra124.c
> > @@ -1071,13 +1071,14 @@ static const struct tegra_mc_client tegra124_mc_clients[] = {
> >   
> >   static const struct tegra_smmu_swgroup tegra124_swgroups[] = {
> >   	{ .name = "dc",        .swgroup = TEGRA_SWGROUP_DC,        .reg = 0x240,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "dcb",       .swgroup = TEGRA_SWGROUP_DCB,       .reg = 0x244,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "afi",       .swgroup = TEGRA_SWGROUP_AFI,       .reg = 0x238 },
> >   	{ .name = "avpc",      .swgroup = TEGRA_SWGROUP_AVPC,      .reg = 0x23c },
> >   	{ .name = "hda",       .swgroup = TEGRA_SWGROUP_HDA,       .reg = 0x254 },
> > -	{ .name = "hc",        .swgroup = TEGRA_SWGROUP_HC,        .reg = 0x250 },
> > +	{ .name = "hc",        .swgroup = TEGRA_SWGROUP_HC,        .reg = 0x250,
> > +	  .use_dma_api = true },
> >   	{ .name = "msenc",     .swgroup = TEGRA_SWGROUP_MSENC,     .reg = 0x264 },
> >   	{ .name = "ppcs",      .swgroup = TEGRA_SWGROUP_PPCS,      .reg = 0x270 },
> >   	{ .name = "sata",      .swgroup = TEGRA_SWGROUP_SATA,      .reg = 0x274 },
> > @@ -1093,7 +1094,8 @@ static const struct tegra_smmu_swgroup tegra124_swgroups[] = {
> >   	{ .name = "sdmmc2a",   .swgroup = TEGRA_SWGROUP_SDMMC2A,   .reg = 0xa98 },
> >   	{ .name = "sdmmc3a",   .swgroup = TEGRA_SWGROUP_SDMMC3A,   .reg = 0xa9c },
> >   	{ .name = "sdmmc4a",   .swgroup = TEGRA_SWGROUP_SDMMC4A,   .reg = 0xaa0 },
> > -	{ .name = "vic",       .swgroup = TEGRA_SWGROUP_VIC,       .reg = 0x284 },
> > +	{ .name = "vic",       .swgroup = TEGRA_SWGROUP_VIC,       .reg = 0x284,
> > +	  .use_dma_api = true },
> >   	{ .name = "vi",        .swgroup = TEGRA_SWGROUP_VI,        .reg = 0x280 },
> >   };
> >   
> > diff --git a/drivers/memory/tegra/tegra30.c b/drivers/memory/tegra/tegra30.c
> > index 0ee4715413ba..df6b5a499ccc 100644
> > --- a/drivers/memory/tegra/tegra30.c
> > +++ b/drivers/memory/tegra/tegra30.c
> > @@ -1140,19 +1140,23 @@ static const struct tegra_mc_client tegra30_mc_clients[] = {
> >   
> >   static const struct tegra_smmu_swgroup tegra30_swgroups[] = {
> >   	{ .name = "dc",   .swgroup = TEGRA_SWGROUP_DC,   .reg = 0x240,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "dcb",  .swgroup = TEGRA_SWGROUP_DCB,  .reg = 0x244,
> > -	  .defer_enable = true },
> > +	  .defer_enable = true, .use_dma_api = true },
> >   	{ .name = "epp",  .swgroup = TEGRA_SWGROUP_EPP,  .reg = 0x248 },
> > -	{ .name = "g2",   .swgroup = TEGRA_SWGROUP_G2,   .reg = 0x24c },
> > +	{ .name = "g2",   .swgroup = TEGRA_SWGROUP_G2,   .reg = 0x24c,
> > +	  .use_dma_api = true },
> >   	{ .name = "mpe",  .swgroup = TEGRA_SWGROUP_MPE,  .reg = 0x264 },
> >   	{ .name = "vi",   .swgroup = TEGRA_SWGROUP_VI,   .reg = 0x280 },
> >   	{ .name = "afi",  .swgroup = TEGRA_SWGROUP_AFI,  .reg = 0x238 },
> >   	{ .name = "avpc", .swgroup = TEGRA_SWGROUP_AVPC, .reg = 0x23c },
> > -	{ .name = "nv",   .swgroup = TEGRA_SWGROUP_NV,   .reg = 0x268 },
> > -	{ .name = "nv2",  .swgroup = TEGRA_SWGROUP_NV2,  .reg = 0x26c },
> > +	{ .name = "nv",   .swgroup = TEGRA_SWGROUP_NV,   .reg = 0x268,
> > +	  .use_dma_api = true },
> > +	{ .name = "nv2",  .swgroup = TEGRA_SWGROUP_NV2,  .reg = 0x26c,
> > +	  .use_dma_api = true },
> >   	{ .name = "hda",  .swgroup = TEGRA_SWGROUP_HDA,  .reg = 0x254 },
> > -	{ .name = "hc",   .swgroup = TEGRA_SWGROUP_HC,   .reg = 0x250 },
> > +	{ .name = "hc",   .swgroup = TEGRA_SWGROUP_HC,   .reg = 0x250,
> > +	  .use_dma_api = true },
> >   	{ .name = "ppcs", .swgroup = TEGRA_SWGROUP_PPCS, .reg = 0x270 },
> >   	{ .name = "sata", .swgroup = TEGRA_SWGROUP_SATA, .reg = 0x278 },
> >   	{ .name = "vde",  .swgroup = TEGRA_SWGROUP_VDE,  .reg = 0x27c },
> > diff --git a/include/soc/tegra/mc.h b/include/soc/tegra/mc.h
> > index ea67972fd585..1cbd990fc0f4 100644
> > --- a/include/soc/tegra/mc.h
> > +++ b/include/soc/tegra/mc.h
> > @@ -78,6 +78,13 @@ struct tegra_smmu_swgroup {
> >   	 * tegra_smmu_enable_translation().
> >   	 */
> >   	bool defer_enable;
> > +
> > +	/*
> > +	 * Set once the clients behind this swgroup are known to work with an
> > +	 * IOMMU_DOMAIN_DMA default domain. All swgroups of a
> > +	 * tegra_smmu_group_soc must agree.
> > +	 */
> > +	bool use_dma_api;
> >   };
> >   
> >   struct tegra_smmu_group_soc {
> > 
> 
>