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

[Adrian Hunter <adrian.hunter@intel.com>]

On 17/04/2026 09:56, Frank Li wrote:
> 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?

hci_dma_dequeue_xfer() handles errors.  It is called from
i3c_hci_process_xfer():
	on timeout:
		calls ->dequeue_xfer() == hci_dma_dequeue_xfer()
	on error:
		calls ->handle_error() == hci_dma_handle_error()
			calls hci_dma_dequeue_xfer()

It takes the spin lock, but has to release it to wait for the
abort.  There is no set time for how long the abort can take,
but the timeout is 1 second, so it is not suitable to wait
for.

> 
> 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@intel.com>
>> ---
>>  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
>>