Merge tag 'drm/tegra/for-5.7-fixes' of git://anongit.freedesktop.org/tegra/linux into drm-fixes

drm/tegra: Fixes for v5.7

This contains a pair of patches which fix SMMU support on Tegra124 and
Tegra210 for host1x and the Tegra DRM driver.

Signed-off-by: Dave Airlie <airlied@redhat.com>

From: Thierry Reding <thierry.reding@gmail.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200508101355.3031268-1-thierry.reding@gmail.com

2 files changed, 57 insertions, 5 deletions

diff --git a/drivers/gpu/drm/tegra/drm.c b/drivers/gpu/drm/tegra/drm.c
index bd268028fb3d..583cd6e0ae27 100644
--- a/drivers/gpu/drm/tegra/drm.c
+++ b/drivers/gpu/drm/tegra/drm.c
@@ -1039,6 +1039,7 @@ void tegra_drm_free(struct tegra_drm *tegra, size_t size, void *virt,
 
 static bool host1x_drm_wants_iommu(struct host1x_device *dev)
 {
+	struct host1x *host1x = dev_get_drvdata(dev->dev.parent);
 	struct iommu_domain *domain;
 
 	/*
@@ -1076,7 +1077,7 @@ static bool host1x_drm_wants_iommu(struct host1x_device *dev)
 	 * sufficient and whether or not the host1x is attached to an IOMMU
 	 * doesn't matter.
 	 */
-	if (!domain && dma_get_mask(dev->dev.parent) <= DMA_BIT_MASK(32))
+	if (!domain && host1x_get_dma_mask(host1x) <= DMA_BIT_MASK(32))
 		return true;
 
 	return domain != NULL;
diff --git a/drivers/gpu/host1x/dev.c b/drivers/gpu/host1x/dev.c
index 388bcc2889aa..d24344e91922 100644
--- a/drivers/gpu/host1x/dev.c
+++ b/drivers/gpu/host1x/dev.c
@@ -192,17 +192,55 @@ static void host1x_setup_sid_table(struct host1x *host)
 	}
 }
 
+static bool host1x_wants_iommu(struct host1x *host1x)
+{
+	/*
+	 * If we support addressing a maximum of 32 bits of physical memory
+	 * and if the host1x firewall is enabled, there's no need to enable
+	 * IOMMU support. This can happen for example on Tegra20, Tegra30
+	 * and Tegra114.
+	 *
+	 * Tegra124 and later can address up to 34 bits of physical memory and
+	 * many platforms come equipped with more than 2 GiB of system memory,
+	 * which requires crossing the 4 GiB boundary. But there's a catch: on
+	 * SoCs before Tegra186 (i.e. Tegra124 and Tegra210), the host1x can
+	 * only address up to 32 bits of memory in GATHER opcodes, which means
+	 * that command buffers need to either be in the first 2 GiB of system
+	 * memory (which could quickly lead to memory exhaustion), or command
+	 * buffers need to be treated differently from other buffers (which is
+	 * not possible with the current ABI).
+	 *
+	 * A third option is to use the IOMMU in these cases to make sure all
+	 * buffers will be mapped into a 32-bit IOVA space that host1x can
+	 * address. This allows all of the system memory to be used and works
+	 * within the limitations of the host1x on these SoCs.
+	 *
+	 * In summary, default to enable IOMMU on Tegra124 and later. For any
+	 * of the earlier SoCs, only use the IOMMU for additional safety when
+	 * the host1x firewall is disabled.
+	 */
+	if (host1x->info->dma_mask <= DMA_BIT_MASK(32)) {
+		if (IS_ENABLED(CONFIG_TEGRA_HOST1X_FIREWALL))
+			return false;
+	}
+
+	return true;
+}
+
 static struct iommu_domain *host1x_iommu_attach(struct host1x *host)
 {
 	struct iommu_domain *domain = iommu_get_domain_for_dev(host->dev);
 	int err;
 
 	/*
-	 * If the host1x firewall is enabled, there's no need to enable IOMMU
-	 * support. Similarly, if host1x is already attached to an IOMMU (via
-	 * the DMA API), don't try to attach again.
+	 * We may not always want to enable IOMMU support (for example if the
+	 * host1x firewall is already enabled and we don't support addressing
+	 * more than 32 bits of physical memory), so check for that first.
+	 *
+	 * Similarly, if host1x is already attached to an IOMMU (via the DMA
+	 * API), don't try to attach again.
 	 */
-	if (IS_ENABLED(CONFIG_TEGRA_HOST1X_FIREWALL) || domain)
+	if (!host1x_wants_iommu(host) || domain)
 		return domain;
 
 	host->group = iommu_group_get(host->dev);
@@ -502,6 +540,19 @@ static void __exit tegra_host1x_exit(void)
 }
 module_exit(tegra_host1x_exit);
 
+/**
+ * host1x_get_dma_mask() - query the supported DMA mask for host1x
+ * @host1x: host1x instance
+ *
+ * Note that this returns the supported DMA mask for host1x, which can be
+ * different from the applicable DMA mask under certain circumstances.
+ */
+u64 host1x_get_dma_mask(struct host1x *host1x)
+{
+	return host1x->info->dma_mask;
+}
+EXPORT_SYMBOL(host1x_get_dma_mask);
+
 MODULE_AUTHOR("Thierry Reding <thierry.reding@avionic-design.de>");
 MODULE_AUTHOR("Terje Bergstrom <tbergstrom@nvidia.com>");
 MODULE_DESCRIPTION("Host1x driver for Tegra products");