linux-kernel - [PATCH 2/5] iommu/dart: Skip reset for locked DARTs

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Message-Id: <20250210-locked-dart-v1-2-5d97fe247f35@rosenzweig.io>
Date: Mon, 10 Feb 2025 14:39:54 -0500
From: Alyssa Rosenzweig <alyssa@...enzweig.io>
To: Sven Peter <sven@...npeter.dev>, Janne Grunau <j@...nau.net>, 
 Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>, 
 Robin Murphy <robin.murphy@....com>
Cc: asahi@...ts.linux.dev, linux-arm-kernel@...ts.infradead.org, 
 iommu@...ts.linux.dev, linux-kernel@...r.kernel.org, 
 Alyssa Rosenzweig <alyssa@...enzweig.io>, Hector Martin <marcan@...can.st>
Subject: [PATCH 2/5] iommu/dart: Skip reset for locked DARTs

Locked DARTs cannot be reconfigured, therefore the reset/restore
procedure can't work and should not be needed. Skip it, allowing locked
DARTs to probe.

Co-developed-by: Hector Martin <marcan@...can.st>
Signed-off-by: Hector Martin <marcan@...can.st>
Signed-off-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
---
 drivers/iommu/apple-dart.c | 24 ++++++++++++------------
 1 file changed, 12 insertions(+), 12 deletions(-)

diff --git a/drivers/iommu/apple-dart.c b/drivers/iommu/apple-dart.c
index 460cf96bc8001e051916f356d5d175b35e36c608..9c74a95eb7e819e94ab2fb47ed0d411a1eba8bf7 100644
--- a/drivers/iommu/apple-dart.c
+++ b/drivers/iommu/apple-dart.c
@@ -452,17 +452,9 @@ apple_dart_t8110_hw_invalidate_tlb(struct apple_dart_stream_map *stream_map)
 
 static int apple_dart_hw_reset(struct apple_dart *dart)
 {
-	u32 config;
 	struct apple_dart_stream_map stream_map;
 	int i;
 
-	config = readl(dart->regs + dart->hw->lock);
-	if (config & dart->hw->lock_bit) {
-		dev_err(dart->dev, "DART is locked down until reboot: %08x\n",
-			config);
-		return -EINVAL;
-	}
-
 	stream_map.dart = dart;
 	bitmap_zero(stream_map.sidmap, DART_MAX_STREAMS);
 	bitmap_set(stream_map.sidmap, 0, dart->num_streams);
@@ -1151,9 +1143,11 @@ static int apple_dart_probe(struct platform_device *pdev)
 	}
 
 	dart->locked = apple_dart_is_locked(dart);
-	ret = apple_dart_hw_reset(dart);
-	if (ret)
-		goto err_clk_disable;
+	if (!dart->locked) {
+		ret = apple_dart_hw_reset(dart);
+		if (ret)
+			goto err_clk_disable;
+	}
 
 	ret = request_irq(dart->irq, dart->hw->irq_handler, IRQF_SHARED,
 			  "apple-dart fault handler", dart);
@@ -1192,7 +1186,9 @@ static void apple_dart_remove(struct platform_device *pdev)
 {
 	struct apple_dart *dart = platform_get_drvdata(pdev);
 
-	apple_dart_hw_reset(dart);
+	if (!dart->locked)
+		apple_dart_hw_reset(dart);
+
 	free_irq(dart->irq, dart);
 
 	iommu_device_unregister(&dart->iommu);
@@ -1325,6 +1321,10 @@ static __maybe_unused int apple_dart_resume(struct device *dev)
 	unsigned int sid, idx;
 	int ret;
 
+	/* Locked DARTs can't be restored, and they should not need it */
+	if (dart->locked)
+		return 0;
+
 	ret = apple_dart_hw_reset(dart);
 	if (ret) {
 		dev_err(dev, "Failed to reset DART on resume\n");

-- 
2.48.1