Re: [PATCH 03/16] i3c: mipi-i3c-hci: Prevent DMA enqueue while ring is aborting or in error

[Frank Li]

On Thu, Apr 16, 2026 at 08:56:51PM +0300, Adrian Hunter wrote:
> Block the DMA enqueue path while a Ring abort is in progress or after an
> error condition has been detected.
>
> Previously, new transfers could be enqueued while the DMA Ring was being
> aborted or while error handling was underway. This allowed enqueue and
> error-recovery paths to run concurrently, potentially interfering with
> each other and corrupting Ring state.

why not hold lock at abort and error handler? does it take quite long time
to do that?

Frank
>
> Introduce explicit enqueue blocking and a wait queue to serialize access:
> enqueue operations now wait until abort or error handling has completed
> before proceeding. Enqueue is unblocked once the Ring is safely restarted.
>
> Signed-off-by: Adrian Hunter <adrian.hunter@xxxxxxxxx>
> ---
>  drivers/i3c/master/mipi-i3c-hci/core.c |  1 +
>  drivers/i3c/master/mipi-i3c-hci/dma.c  | 25 +++++++++++++++++++++++--
>  drivers/i3c/master/mipi-i3c-hci/hci.h  |  2 ++
>  3 files changed, 26 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/i3c/master/mipi-i3c-hci/core.c b/drivers/i3c/master/mipi-i3c-hci/core.c
> index bb8f2d830b0d..5e1bc6d819cf 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/core.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/core.c
> @@ -976,6 +976,7 @@ static int i3c_hci_probe(struct platform_device *pdev)
>
>  	spin_lock_init(&hci->lock);
>  	mutex_init(&hci->control_mutex);
> +	init_waitqueue_head(&hci->enqueue_wait_queue);
>
>  	/*
>  	 * Multi-bus instances share the same MMIO address range, but not
> diff --git a/drivers/i3c/master/mipi-i3c-hci/dma.c b/drivers/i3c/master/mipi-i3c-hci/dma.c
> index 4cd32e3afa7b..314635e6e190 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/dma.c
> +++ b/drivers/i3c/master/mipi-i3c-hci/dma.c
> @@ -484,6 +484,12 @@ static int hci_dma_queue_xfer(struct i3c_hci *hci,
>
>  	spin_lock_irq(&hci->lock);
>
> +	while (unlikely(hci->enqueue_blocked)) {
> +		spin_unlock_irq(&hci->lock);
> +		wait_event(hci->enqueue_wait_queue, !READ_ONCE(hci->enqueue_blocked));
> +		spin_lock_irq(&hci->lock);
> +	}
> +
>  	if (n > rh->xfer_space) {
>  		spin_unlock_irq(&hci->lock);
>  		hci_dma_unmap_xfer(hci, xfer_list, n);
> @@ -539,6 +545,14 @@ static int hci_dma_queue_xfer(struct i3c_hci *hci,
>  	return 0;
>  }
>
> +static void hci_dma_unblock_enqueue(struct i3c_hci *hci)
> +{
> +	if (hci->enqueue_blocked) {
> +		hci->enqueue_blocked = false;
> +		wake_up_all(&hci->enqueue_wait_queue);
> +	}
> +}
> +
>  static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
>  				 struct hci_xfer *xfer_list, int n)
>  {
> @@ -550,12 +564,17 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
>
>  	guard(mutex)(&hci->control_mutex);
>
> +	spin_lock_irq(&hci->lock);
> +
>  	ring_status = rh_reg_read(RING_STATUS);
>  	if (ring_status & RING_STATUS_RUNNING) {
> +		hci->enqueue_blocked = true;
> +		spin_unlock_irq(&hci->lock);
>  		/* stop the ring */
>  		reinit_completion(&rh->op_done);
>  		rh_reg_write(RING_CONTROL, rh_reg_read(RING_CONTROL) | RING_CTRL_ABORT);
>  		wait_for_completion_timeout(&rh->op_done, HZ);
> +		spin_lock_irq(&hci->lock);
>  		ring_status = rh_reg_read(RING_STATUS);
>  		if (ring_status & RING_STATUS_RUNNING) {
>  			/*
> @@ -567,8 +586,6 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
>  		}
>  	}
>
> -	spin_lock_irq(&hci->lock);
> -
>  	for (i = 0; i < n; i++) {
>  		struct hci_xfer *xfer = xfer_list + i;
>  		int idx = xfer->ring_entry;
> @@ -604,6 +621,8 @@ static bool hci_dma_dequeue_xfer(struct i3c_hci *hci,
>  	rh_reg_write(RING_CONTROL, RING_CTRL_ENABLE);
>  	rh_reg_write(RING_CONTROL, RING_CTRL_ENABLE | RING_CTRL_RUN_STOP);
>
> +	hci_dma_unblock_enqueue(hci);
> +
>  	spin_unlock_irq(&hci->lock);
>
>  	return did_unqueue;
> @@ -647,6 +666,8 @@ static void hci_dma_xfer_done(struct i3c_hci *hci, struct hci_rh_data *rh)
>  			}
>  			if (xfer->completion)
>  				complete(xfer->completion);
> +			if (RESP_STATUS(resp))
> +				hci->enqueue_blocked = true;
>  		}
>
>  		done_ptr = (done_ptr + 1) % rh->xfer_entries;
> diff --git a/drivers/i3c/master/mipi-i3c-hci/hci.h b/drivers/i3c/master/mipi-i3c-hci/hci.h
> index f17f43494c1b..d630400ec945 100644
> --- a/drivers/i3c/master/mipi-i3c-hci/hci.h
> +++ b/drivers/i3c/master/mipi-i3c-hci/hci.h
> @@ -54,6 +54,8 @@ struct i3c_hci {
>  	struct mutex control_mutex;
>  	atomic_t next_cmd_tid;
>  	bool irq_inactive;
> +	bool enqueue_blocked;
> +	wait_queue_head_t enqueue_wait_queue;
>  	u32 caps;
>  	unsigned int quirks;
>  	unsigned int DAT_entries;
> --
> 2.51.0
>