iommu/tegra: Add tegra_dev_iommu_get_stream_id() helper

Bugzilla: https://bugzilla.redhat.com/show_bug.cgi?id=2144641

Conflicts:
	include/linux/iommu.h
	No backport of commit fa49364 "iommu/dma: Move public
	interfaces to linux/iommu.h" causes context conflict.

commit 493c9b6
Author: Thierry Reding <treding@nvidia.com>
Date: Tue, 6 Dec 2022 17:59:41 +0100

    Access to the internals of struct iommu_fwspec by non-IOMMU drivers is
    discouraged. Many drivers for Tegra SoCs, however, need access to their
    IOMMU stream IDs so that they can be programmed into various hardware
    registers.

    Formalize this access into a common helper to make it easier to audit
    and maintain.

    Acked-by: Robin Murphy <robin.murphy@arm.com>
    Signed-off-by: Thierry Reding <treding@nvidia.com>
    Link: https://lore.kernel.org/r/20221206165945.3551774-3-thierry.reding@gmail.com
    Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>

Signed-off-by: Mark Salter <msalter@redhat.com>

Author: mosalter

include/linux/iommu.h

@@ -1070,4 +1070,25 @@ void iommu_debugfs_setup(void);
 static inline void iommu_debugfs_setup(void) {}
 #endif
 
+/*
+ * Newer generations of Tegra SoCs require devices' stream IDs to be directly programmed into
+ * some registers. These are always paired with a Tegra SMMU or ARM SMMU, for which the contents
+ * of the struct iommu_fwspec are known. Use this helper to formalize access to these internals.
+ */
+#define TEGRA_STREAM_ID_BYPASS 0x7f
+
+static inline bool tegra_dev_iommu_get_stream_id(struct device *dev, u32 *stream_id)
+{
+#ifdef CONFIG_IOMMU_API
+	struct iommu_fwspec *fwspec = dev_iommu_fwspec_get(dev);
+
+	if (fwspec && fwspec->num_ids == 1) {
+		*stream_id = fwspec->ids[0] & 0xffff;
+		return true;
+	}
+#endif
+
+	return false;
+}
+
 #endif /* __LINUX_IOMMU_H */