On Sun, Mar 28, 2021 at 09:40:09AM +0200, Sven Peter wrote:

Apple's new SoCs use iommus for almost all peripherals. These Device
Address Resolution Tables must be setup before these peripherals can
act as DMA masters.

Signed-off-by: Sven Peter <redacted>
---
 MAINTAINERS                      |   1 +
 drivers/iommu/Kconfig            |  14 +
 drivers/iommu/Makefile           |   1 +
 drivers/iommu/apple-dart-iommu.c | 858 +++++++++++++++++++++++++++++++
 4 files changed, 874 insertions(+)
 create mode 100644 drivers/iommu/apple-dart-iommu.c

[...]

+/* must be called with held domain->lock */
+static int apple_dart_attach_stream(struct apple_dart_domain *domain,
+				    struct apple_dart *dart, u32 sid)
+{
+	unsigned long flags;
+	struct apple_dart_stream *stream;
+	struct io_pgtable_cfg *pgtbl_cfg;
+	int ret;
+
+	list_for_each_entry(stream, &domain->streams, stream_head) {
+		if (stream->dart == dart && stream->sid == sid) {
+			stream->num_devices++;
+			return 0;
+		}
+	}
+
+	spin_lock_irqsave(&dart->lock, flags);
+
+	if (WARN_ON(dart->used_sids & BIT(sid))) {
+		ret = -EINVAL;
+		goto error;
+	}
+
+	stream = kzalloc(sizeof(*stream), GFP_KERNEL);
+	if (!stream) {
+		ret = -ENOMEM;
+		goto error;
+	}

Just in case you missed it, a cocci bot noticed that you're using GFP_KERNEL
to allocate while holding a spinlock here:

https://lore.kernel.org/r/alpine.DEB.2.22.394.2104041724340.2958@hadrien (local)

Will

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