ptdma: pt_core_execute_cmd() should use spinlock

The interrupt handler (pt_core_irq_handler()) of the ptdma
driver can be called from interrupt context. The code flow
in this function can lead down to pt_core_execute_cmd() which
will attempt to grab a mutex, which is not appropriate in
interrupt context and ultimately leads to a kernel panic.
The fix here changes this mutex to a spinlock, which has
been verified to resolve the issue.

Fixes: fa5d823b ("dmaengine: ptdma: Initial driver for the AMD PTDMA")
Signed-off-by: Eric Pilmore <epilmore@gigaio.com>
Link: https://lore.kernel.org/r/20230119033907.35071-1-epilmore@gigaio.comSigned-off-by: Vinod Koul <vkoul@kernel.org>

drivers/dma/ptdma/ptdma-dev.c

@@ -71,12 +71,13 @@ static int pt_core_execute_cmd(struct ptdma_desc *desc, struct pt_cmd_queue *cmd
 	bool soc = FIELD_GET(DWORD0_SOC, desc->dw0);
 	u8 *q_desc = (u8 *)&cmd_q->qbase[cmd_q->qidx];
 	u32 tail;
+	unsigned long flags;
 
 	if (soc) {
 		desc->dw0 |= FIELD_PREP(DWORD0_IOC, desc->dw0);
 		desc->dw0 &= ~DWORD0_SOC;
 	}
-	mutex_lock(&cmd_q->q_mutex);
+	spin_lock_irqsave(&cmd_q->q_lock, flags);
 
 	/* Copy 32-byte command descriptor to hw queue. */
 	memcpy(q_desc, desc, 32);
@@ -91,7 +92,7 @@ static int pt_core_execute_cmd(struct ptdma_desc *desc, struct pt_cmd_queue *cmd
 
 	/* Turn the queue back on using our cached control register */
 	pt_start_queue(cmd_q);
-	mutex_unlock(&cmd_q->q_mutex);
+	spin_unlock_irqrestore(&cmd_q->q_lock, flags);
 
 	return 0;
 }
@@ -199,7 +200,7 @@ int pt_core_init(struct pt_device *pt)
 
 	cmd_q->pt = pt;
 	cmd_q->dma_pool = dma_pool;
-	mutex_init(&cmd_q->q_mutex);
+	spin_lock_init(&cmd_q->q_lock);
 
 	/* Page alignment satisfies our needs for N <= 128 */
 	cmd_q->qsize = Q_SIZE(Q_DESC_SIZE);

drivers/dma/ptdma/ptdma.h

@@ -196,7 +196,7 @@ struct pt_cmd_queue {
 	struct ptdma_desc *qbase;
 
 	/* Aligned queue start address (per requirement) */
-	struct mutex q_mutex ____cacheline_aligned;
+	spinlock_t q_lock ____cacheline_aligned;
 	unsigned int qidx;
 
 	unsigned int qsize;