Re: [PATCH v1 1/2] iommu/tegra-smmu: Defer attachment of display clients

[Nicolin Chen <nicoleotsuka@gmail.com>]

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On Mon, Mar 29, 2021 at 02:32:55AM +0300, Dmitry Osipenko wrote:
> All consumer-grade Android and Chromebook devices show a splash screen
> on boot and then display is left enabled when kernel is booted. This
> behaviour is unacceptable in a case of implicit IOMMU domains to which
> devices are attached during kernel boot since devices, like display
> controller, may perform DMA at that time. We can work around this problem
> by deferring the enable of SMMU translation for a specific devices,
> like a display controller, until the first IOMMU mapping is created,
> which works good enough in practice because by that time h/w is already
> stopped.
> 
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>

For both patches:
Acked-by: Nicolin Chen <nicoleotsuka@gmail.com>
Tested-by: Nicolin Chen <nicoleotsuka@gmail.com>

The WAR looks good to me. Perhaps Thierry would give some input.

Another topic:
I think this may help work around the mc-errors, which we have
been facing on Tegra210 also when we enable IOMMU_DOMAIN_DMA.
(attached a test patch rebasing on these two)

However, GPU would also report errors using DMA domain:

 nouveau 57000000.gpu: acr: firmware unavailable
 nouveau 57000000.gpu: pmu: firmware unavailable
 nouveau 57000000.gpu: gr: firmware unavailable
 tegra-mc 70019000.memory-controller: gpusrd: read @0x00000000fffbe200: Security violation (TrustZone violation)
 nouveau 57000000.gpu: DRM: failed to create kernel channel, -22
 tegra-mc 70019000.memory-controller: gpusrd: read @0x00000000fffad000: Security violation (TrustZone violation)
 nouveau 57000000.gpu: fifo: SCHED_ERROR 20 []
 nouveau 57000000.gpu: fifo: SCHED_ERROR 20 []

Looking at the address, seems that GPU allocated memory in 32-bit
physical address space behind SMMU, so a violation happened after
turning on DMA domain I guess... 

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From 20b58a74fee0c7b961b92f9118ad69a12199e6a5 Mon Sep 17 00:00:00 2001
From: Nicolin Chen <nicolinc@nvidia.com>
Date: Thu, 12 Dec 2019 17:46:50 -0800
Subject: [PATCH 6/7] iommu/tegra-smmu: Add IOMMU_DOMAIN_DMA

Signed-off-by: Nicolin Chen <nicolinc@nvidia.com>
---
 drivers/iommu/tegra-smmu.c | 39 ++++++++++++++++++++++----------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/drivers/iommu/tegra-smmu.c b/drivers/iommu/tegra-smmu.c
index 8104f001e679..eff10d1ec568 100644
--- a/drivers/iommu/tegra-smmu.c
+++ b/drivers/iommu/tegra-smmu.c
@@ -15,6 +15,7 @@
 #include <linux/slab.h>
 #include <linux/spinlock.h>
 #include <linux/dma-mapping.h>
+#include <linux/dma-iommu.h>
 
 #include <soc/tegra/ahb.h>
 #include <soc/tegra/mc.h>
@@ -297,35 +298,29 @@ static struct iommu_domain *tegra_smmu_domain_alloc(unsigned type)
 {
 	struct tegra_smmu_as *as;
 
-	if (type != IOMMU_DOMAIN_UNMANAGED)
+	if (type != IOMMU_DOMAIN_UNMANAGED && type != IOMMU_DOMAIN_DMA)
 		return NULL;
 
 	as = kzalloc(sizeof(*as), GFP_KERNEL);
 	if (!as)
 		return NULL;
 
+	if (type == IOMMU_DOMAIN_DMA && iommu_get_dma_cookie(&as->domain))
+		goto free_as;
+
 	as->attr = SMMU_PD_READABLE | SMMU_PD_WRITABLE | SMMU_PD_NONSECURE;
 
 	as->pd = alloc_page(GFP_KERNEL | __GFP_DMA | __GFP_ZERO);
-	if (!as->pd) {
-		kfree(as);
-		return NULL;
-	}
+	if (!as->pd)
+		goto put_dma_cookie;
 
 	as->count = kcalloc(SMMU_NUM_PDE, sizeof(u32), GFP_KERNEL);
-	if (!as->count) {
-		__free_page(as->pd);
-		kfree(as);
-		return NULL;
-	}
+	if (!as->count)
+		goto free_pd_range;
 
 	as->pts = kcalloc(SMMU_NUM_PDE, sizeof(*as->pts), GFP_KERNEL);
-	if (!as->pts) {
-		kfree(as->count);
-		__free_page(as->pd);
-		kfree(as);
-		return NULL;
-	}
+	if (!as->pts)
+		goto free_pts;
 
 	spin_lock_init(&as->lock);
 
@@ -335,6 +330,17 @@ static struct iommu_domain *tegra_smmu_domain_alloc(unsigned type)
 	as->attached_devices_need_sync = true;
 
 	return &as->domain;
+
+free_pts:
+	kfree(as->pts);
+free_pd_range:
+	__free_page(as->pd);
+put_dma_cookie:
+	iommu_put_dma_cookie(&as->domain);
+free_as:
+	kfree(as);
+
+	return NULL;
 }
 
 static void tegra_smmu_domain_free(struct iommu_domain *domain)
@@ -346,6 +352,7 @@ static void tegra_smmu_domain_free(struct iommu_domain *domain)
 	WARN_ON_ONCE(as->use_count);
 	kfree(as->count);
 	kfree(as->pts);
+	iommu_put_dma_cookie(domain);
 	kfree(as);
 }
 
-- 
2.17.1