linux-kernel - [PATCH RFC 1/2 stable-6.1] dmaengine: at_hdmac: get next dma transfer from the right list

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Date:   Tue, 14 Nov 2023 13:22:06 +0100
From:   Thomas Pfaff <tpfaff@....com>
To:     <ludovic.desroches@...rochip.com>, <tudor.ambarus@...rochip.com>
CC:     <nicolas.ferre@...rochip.com>, <vkoul@...nel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH RFC 1/2 stable-6.1] dmaengine: at_hdmac: get next dma transfer
 from the right list

From: Thomas Pfaff <tpfaff@....com>

In kernel 6.1, atc_advance_work and atc_handle_error are checking for the 
next dma transfer inside active list, but the descriptor is taken from the 
queue instead.

Signed-off-by: Thomas Pfaff <tpfaff@....com>
---
diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 858bd64f1313..68c1bfbefc5c 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -490,6 +490,27 @@ atc_chain_complete(struct at_dma_chan *atchan, struct at_desc *desc)
 	}
 }
 
+/**
+ * atc_start_next - start next pending transaction if any
+ * @atchan: channel where the transaction ended
+ *
+ * Called with atchan->lock held
+ */
+static void atc_start_next(struct at_dma_chan *atchan)
+{
+	struct at_desc *desc = NULL;
+
+	if (!list_empty(&atchan->active_list))
+		desc = atc_first_active(atchan);
+	else if (!list_empty(&atchan->queue)) {
+		desc = atc_first_queued(atchan);
+		list_move_tail(&desc->desc_node, &atchan->active_list);
+	}
+
+	if (desc)
+		atc_dostart(atchan, desc);
+}
+
 /**
  * atc_advance_work - at the end of a transaction, move forward
  * @atchan: channel where the transaction ended
@@ -513,11 +534,7 @@ static void atc_advance_work(struct at_dma_chan *atchan)
 
 	/* advance work */
 	spin_lock_irqsave(&atchan->lock, flags);
-	if (!list_empty(&atchan->active_list)) {
-		desc = atc_first_queued(atchan);
-		list_move_tail(&desc->desc_node, &atchan->active_list);
-		atc_dostart(atchan, desc);
-	}
+	atc_start_next(atchan);
 	spin_unlock_irqrestore(&atchan->lock, flags);
 }
 
@@ -529,7 +546,6 @@ static void atc_advance_work(struct at_dma_chan *atchan)
 static void atc_handle_error(struct at_dma_chan *atchan)
 {
 	struct at_desc *bad_desc;
-	struct at_desc *desc;
 	struct at_desc *child;
 	unsigned long flags;
 
@@ -543,11 +559,7 @@ static void atc_handle_error(struct at_dma_chan *atchan)
 	list_del_init(&bad_desc->desc_node);
 
 	/* Try to restart the controller */
-	if (!list_empty(&atchan->active_list)) {
-		desc = atc_first_queued(atchan);
-		list_move_tail(&desc->desc_node, &atchan->active_list);
-		atc_dostart(atchan, desc);
-	}
+	atc_start_next(atchan);
 
 	/*
 	 * KERN_CRITICAL may seem harsh, but since this only happens