Re: [PATCH V2 5/5] dmaengine: xilinx_dma: Add support for reporting transfer size to AXI DMA / MCDMA client when app fields are unavailable

["Neeli, Srinivas" <srneeli@amd.com>]

Hi Frank,

On 3/30/2026 9:34 PM, Frank Li wrote:
> On Fri, Mar 13, 2026 at 11:55:33AM +0530, Srinivas Neeli wrote:
>> From: Suraj Gupta <suraj.gupta2@amd.com>
>>
>> The AXI4-stream status and control interface is optional in the AXI DMA /
>> MCDMA IP design; when it is not present, app fields are not available in
>> DMA descriptor. In such cases, the transferred byte count can be
>> communicated to the client using the status field (bits 0-25) of
>> AXI DMA / MCDMA descriptor.
>>
>> Add a xferred_bytes field to struct xilinx_dma_tx_descriptor to record the
>> number of bytes transferred for each transaction. The value is calculated
>> using the existing xilinx_dma_get_residue() function, which traverses all
>> hardware descriptors associated with the async transaction descriptor,
>> avoiding redundant traversal.
> Can you split this change to new patch?
>
> Frank
The changes related to the xferred_bytes field and the 
has_stsctrl_stream property are tightly coupled and cannot be cleanly 
separated without breaking functionality or resulting in incomplete commits.
The xferred_bytes field does not serve any meaningful purpose without 
the has_stsctrl_stream check:
- xferred_bytes is computed in xilinx_dma_get_residue(), but it is only 
exposed to clients through xilinx_dma_get_metadata_ptr().
- The metadata accessor relies on has_stsctrl_stream to determine 
whether to return APP fields or xferred_bytes.
- Without this conditional logic, xferred_bytes would still be 
calculated but would never be consumed by any client


Thanks

Neeli Srinivas

>> The driver uses the xlnx,include-stscntrl-strm device tree property to
>> determine if the status/control stream interface is present and selects the
>> appropriate metadata source accordingly.
>>
>> Signed-off-by: Suraj Gupta <suraj.gupta2@amd.com>
>> ---
>>   drivers/dma/xilinx/xilinx_dma.c | 28 ++++++++++++++++++++++++----
>>   1 file changed, 24 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/dma/xilinx/xilinx_dma.c b/drivers/dma/xilinx/xilinx_dma.c
>> index 52203d44e7a4..f5ef03a1297c 100644
>> --- a/drivers/dma/xilinx/xilinx_dma.c
>> +++ b/drivers/dma/xilinx/xilinx_dma.c
>> @@ -380,6 +380,8 @@ struct xilinx_cdma_tx_segment {
>>    * @cyclic: Check for cyclic transfers.
>>    * @err: Whether the descriptor has an error.
>>    * @residue: Residue of the completed descriptor
>> + * @xferred_bytes: Number of bytes transferred by this transaction
>> + *                 descriptor.
>>    */
>>   struct xilinx_dma_tx_descriptor {
>>   	struct xilinx_dma_chan *chan;
>> @@ -389,6 +391,7 @@ struct xilinx_dma_tx_descriptor {
>>   	bool cyclic;
>>   	bool err;
>>   	u32 residue;
>> +	u32 xferred_bytes;
>>   };
>>
>>   /**
>> @@ -515,6 +518,7 @@ struct xilinx_dma_config {
>>    * @mm2s_chan_id: DMA mm2s channel identifier
>>    * @max_buffer_len: Max buffer length
>>    * @has_axistream_connected: AXI DMA connected to AXI Stream IP
>> + * @has_stsctrl_stream: AXI4-stream status and control interface is enabled
>>    */
>>   struct xilinx_dma_device {
>>   	void __iomem *regs;
>> @@ -534,6 +538,7 @@ struct xilinx_dma_device {
>>   	u32 mm2s_chan_id;
>>   	u32 max_buffer_len;
>>   	bool has_axistream_connected;
>> +	bool has_stsctrl_stream;
>>   };
>>
>>   /* Macros */
>> @@ -672,8 +677,12 @@ static void *xilinx_dma_get_metadata_ptr(struct dma_async_tx_descriptor *tx,
>>   				       struct xilinx_axidma_tx_segment, node);
>>   		metadata_ptr = seg->hw.app;
>>   	}
>> -	*max_len = *payload_len = sizeof(u32) * XILINX_DMA_NUM_APP_WORDS;
>> -	return metadata_ptr;
>> +	if (desc->chan->xdev->has_stsctrl_stream) {
>> +		*max_len = *payload_len = sizeof(u32) * XILINX_DMA_NUM_APP_WORDS;
>> +		return metadata_ptr;
>> +	}
>> +	*max_len = *payload_len = sizeof(desc->xferred_bytes);
>> +	return (void *)&desc->xferred_bytes;
>>   }
>>
>>   static struct dma_descriptor_metadata_ops xilinx_dma_metadata_ops = {
>> @@ -864,6 +873,7 @@ xilinx_dma_alloc_tx_descriptor(struct xilinx_dma_chan *chan)
>>   		return NULL;
>>
>>   	desc->chan = chan;
>> +	desc->xferred_bytes = 0;
>>   	INIT_LIST_HEAD(&desc->segments);
>>
>>   	return desc;
>> @@ -1014,6 +1024,7 @@ static u32 xilinx_dma_get_residue(struct xilinx_dma_chan *chan,
>>   	struct xilinx_aximcdma_desc_hw *aximcdma_hw;
>>   	struct list_head *entry;
>>   	u32 residue = 0;
>> +	u32 xferred = 0;
>>
>>   	list_for_each(entry, &desc->segments) {
>>   		if (chan->xdev->dma_config->dmatype == XDMA_TYPE_CDMA) {
>> @@ -1031,25 +1042,32 @@ static u32 xilinx_dma_get_residue(struct xilinx_dma_chan *chan,
>>   			axidma_hw = &axidma_seg->hw;
>>   			residue += (axidma_hw->control - axidma_hw->status) &
>>   				   chan->xdev->max_buffer_len;
>> +			xferred += axidma_hw->status & chan->xdev->max_buffer_len;
>>   		} else {
>>   			aximcdma_seg =
>>   				list_entry(entry,
>>   					   struct xilinx_aximcdma_tx_segment,
>>   					   node);
>>   			aximcdma_hw = &aximcdma_seg->hw;
>> -			if (chan->direction == DMA_DEV_TO_MEM)
>> +			if (chan->direction == DMA_DEV_TO_MEM) {
>>   				residue +=
>>   					(aximcdma_hw->control -
>>   					 aximcdma_hw->s2mm_status) &
>>   					chan->xdev->max_buffer_len;
>> -			else
>> +				xferred += aximcdma_hw->s2mm_status &
>> +					chan->xdev->max_buffer_len;
>> +			} else {
>>   				residue +=
>>   					(aximcdma_hw->control -
>>   					 aximcdma_hw->mm2s_status) &
>>   					chan->xdev->max_buffer_len;
>> +				xferred += aximcdma_hw->mm2s_status &
>> +					chan->xdev->max_buffer_len;
>> +			}
>>   		}
>>   	}
>>
>> +	desc->xferred_bytes = xferred;
>>   	return residue;
>>   }
>>
>> @@ -3284,6 +3302,8 @@ static int xilinx_dma_probe(struct platform_device *pdev)
>>   	    xdev->dma_config->dmatype == XDMA_TYPE_AXIMCDMA) {
>>   		xdev->has_axistream_connected =
>>   			of_property_read_bool(node, "xlnx,axistream-connected");
>> +		xdev->has_stsctrl_stream =
>> +			of_property_read_bool(node, "xlnx,include-stscntrl-strm");
>>   	}
>>
>>   	if (xdev->dma_config->dmatype == XDMA_TYPE_VDMA) {
>> --
>> 2.43.0
>>