Re: [PATCH 06/14] qcom: mtd: nand: add bam dma descriptor handling

[Abhishek Sahu <absahu@codeaurora.org>]

On 2017-07-04 11:40, Archit Taneja wrote:
> On 06/29/2017 12:45 PM, Abhishek Sahu wrote:
>> 1. prepare_bam_async_desc is the function which will call
>>     all the DMA API’s. It will fetch the outstanding scatter gather
>>     list for passed channel and will do the DMA descriptor formation.
>>     The DMA flag is dependent upon the type of channel.
>> 
>> 2. For ADM DMA, the descriptor is being formed for every DMA
>>     request so its sgl count will be always 1 while in BAM DMA, the
>>     clubbing of descriptor is being done to increase throughput.
>> 
>> 3. ADM uses only one channel while in BAM, data descriptors
>>     will be submitted to tx channel (for write) or rx channel
>>     (for read) and all the registers read/write descriptors in
>>     command channel.
>> 
>> Signed-off-by: Abhishek Sahu <absahu@codeaurora.org>
>> ---
>>   drivers/mtd/nand/qcom_nandc.c | 119 
>> ++++++++++++++++++++++++++++++++++++++++--
>>   1 file changed, 114 insertions(+), 5 deletions(-)
>> 
>> diff --git a/drivers/mtd/nand/qcom_nandc.c 
>> b/drivers/mtd/nand/qcom_nandc.c
>> index f8d0bde..7042a65 100644
>> --- a/drivers/mtd/nand/qcom_nandc.c
>> +++ b/drivers/mtd/nand/qcom_nandc.c
>> @@ -206,14 +206,22 @@ struct bam_transaction {
>>    * This data type corresponds to the nand dma descriptor
>>    * @list - list for desc_info
>>    * @dir - DMA transfer direction
>> - * @sgl - sgl which will be used for single sgl dma descriptor
>> + * @sgl - sgl which will be used for single sgl dma descriptor. Only 
>> used by ADM
>> + * @bam_sgl - sgl which will be used for dma descriptor. Only used by 
>> BAM
>> + * @sgl_cnt - number of SGL in bam_sgl. Only used by BAM
>>    * @dma_desc - low level dma engine descriptor
>>    */
>>   struct desc_info {
>>   	struct list_head node;
>> 
>>   	enum dma_data_direction dir;
>> -	struct scatterlist sgl;
>> +	union {
>> +			struct scatterlist sgl;
> 
> Can you make this adm_sgl instead for consistency? Also, please use 
> only
> two tabs instead of one here for indentation.

  Sure. I will do the same in v2.

> 
>> +			struct {
>> +				struct scatterlist *bam_sgl;
>> +				int sgl_cnt;
>> +			};
>> +	};
>>   	struct dma_async_tx_descriptor *dma_desc;
>>   };
>> 
>> @@ -564,6 +572,68 @@ static void update_rw_regs(struct qcom_nand_host 
>> *host, int num_cw, bool read)
>>   	nandc_set_reg(nandc, NAND_EXEC_CMD, 1);
>>   }
>> 
>> +/*
>> + * Maps the scatter gather list for DMA transfer and forms the DMA 
>> descriptor
>> + * for BAM. This descriptor will be added in the NAND DMA descriptor 
>> queue
>> + * which will be submitted to DMA engine.
>> + */
>> +static int prepare_bam_async_desc(struct qcom_nand_controller *nandc,
>> +				  struct dma_chan *chan,
>> +				  unsigned long flags)
> 
> From what I gathered in patch #10, this would be called by
> prep_dma_desc_data_bam() and prep_dma_desc_command(). Can you rename 
> these
> two to something like prep_bam_dma_desc_data() and 
> prep_bam_dma_desc_cmd()
> 

  Sure. I will do the same in v2.

> 
>> +{
>> +	struct desc_info *desc;
>> +	struct scatterlist *sgl;
>> +	unsigned int sgl_cnt;
>> +	struct bam_transaction *bam_txn = nandc->bam_txn;
>> +	enum dma_transfer_direction dir_eng;
>> +	struct dma_async_tx_descriptor *dma_desc;
>> +
>> +	desc = kzalloc(sizeof(*desc), GFP_KERNEL);
>> +	if (!desc)
>> +		return -ENOMEM;
>> +
>> +	if (chan == nandc->cmd_chan) {
>> +		sgl = &bam_txn->cmd_sgl[bam_txn->cmd_sgl_start];
>> +		sgl_cnt = bam_txn->cmd_sgl_pos - bam_txn->cmd_sgl_start;
>> +		bam_txn->cmd_sgl_start = bam_txn->cmd_sgl_pos;
>> +		dir_eng = DMA_MEM_TO_DEV;
>> +		desc->dir = DMA_TO_DEVICE;
>> +	} else if (chan == nandc->tx_chan) {
>> +		sgl = &bam_txn->data_sg[bam_txn->tx_sgl_start];
>> +		sgl_cnt = bam_txn->tx_sgl_pos - bam_txn->tx_sgl_start;
>> +		bam_txn->tx_sgl_start = bam_txn->tx_sgl_pos;
>> +		dir_eng = DMA_MEM_TO_DEV;
>> +		desc->dir = DMA_TO_DEVICE;
>> +	} else {
>> +		sgl = &bam_txn->data_sg[bam_txn->rx_sgl_start];
>> +		sgl_cnt = bam_txn->rx_sgl_pos - bam_txn->rx_sgl_start;
>> +		bam_txn->rx_sgl_start = bam_txn->rx_sgl_pos;
>> +		desc->dir = DMA_FROM_DEVICE;
>> +		dir_eng = DMA_DEV_TO_MEM;
>> +	}
>> +
>> +	sg_mark_end(sgl + sgl_cnt - 1);
>> +	dma_map_sg(nandc->dev, sgl, sgl_cnt, desc->dir);
> 
> Is it safe to assume here that dma_map_sg won't return an error?
> 

  We need to check for error. I will fix this in v2.

>> +
>> +	desc->sgl_cnt = sgl_cnt;
>> +	desc->bam_sgl = sgl;
>> +
>> +	dma_desc = dmaengine_prep_slave_sg(chan, sgl, sgl_cnt, dir_eng,
>> +					   flags);
>> +
>> +	if (!dma_desc) {
>> +		dev_err(nandc->dev, "failure in prep desc\n");
>> +		kfree(desc);
>> +		return -EINVAL;
>> +	}
>> +
>> +	desc->dma_desc = dma_desc;
>> +
>> +	list_add_tail(&desc->node, &nandc->desc_list);
>> +
>> +	return 0;
>> +}
>> +
> 
> 
>>   static int prep_dma_desc(struct qcom_nand_controller *nandc, bool 
>> read,
>>   			 int reg_off, const void *vaddr, int size,
>>   			 bool flow_control)
> 
> Could you rename this to prep_adm_dma_desc for consistency?
> 
>> @@ -891,12 +961,44 @@ static int submit_descs(struct 
>> qcom_nand_controller *nandc)
>>   {
>>   	struct desc_info *desc;
>>   	dma_cookie_t cookie = 0;
>> +	struct bam_transaction *bam_txn = nandc->bam_txn;
>> +	int r;
>> +
>> +	if (nandc->dma_bam_enabled) {
>> +		if (bam_txn->rx_sgl_pos - bam_txn->rx_sgl_start) {
> 
> Using '>' instead of '-' here should be more legible.
> 

  Yes. I will use the same in v2.

>> +			r = prepare_bam_async_desc(nandc, nandc->rx_chan, 0);
>> +			if (r)
>> +				return r;
>> +		}
>> +
>> +		if (bam_txn->tx_sgl_pos - bam_txn->tx_sgl_start) {
>> +			r = prepare_bam_async_desc(nandc, nandc->tx_chan,
>> +						   DMA_PREP_INTERRUPT);
>> +			if (r)
>> +				return r;
>> +		}
>> +
>> +		if (bam_txn->cmd_sgl_pos - bam_txn->cmd_sgl_start) {
>> +			r = prepare_bam_async_desc(nandc, nandc->cmd_chan,
>> +						   DMA_PREP_CMD);
>> +			if (r)
>> +				return r;
>> +		}
>> +	}
>> 
>>   	list_for_each_entry(desc, &nandc->desc_list, node)
>>   		cookie = dmaengine_submit(desc->dma_desc);
>> 
>> -	if (dma_sync_wait(nandc->chan, cookie) != DMA_COMPLETE)
>> -		return -ETIMEDOUT;
>> +	if (nandc->dma_bam_enabled) {
>> +		dma_async_issue_pending(nandc->tx_chan);
>> +		dma_async_issue_pending(nandc->rx_chan);
>> +
>> +		if (dma_sync_wait(nandc->cmd_chan, cookie) != DMA_COMPLETE)
>> +			return -ETIMEDOUT;
>> +	} else {
>> +		if (dma_sync_wait(nandc->chan, cookie) != DMA_COMPLETE)
>> +			return -ETIMEDOUT;
>> +	}
>> 
>>   	return 0;
>>   }
>> @@ -907,7 +1009,14 @@ static void free_descs(struct 
>> qcom_nand_controller *nandc)
>> 
>>   	list_for_each_entry_safe(desc, n, &nandc->desc_list, node) {
>>   		list_del(&desc->node);
>> -		dma_unmap_sg(nandc->dev, &desc->sgl, 1, desc->dir);
>> +
>> +		if (nandc->dma_bam_enabled)
>> +			dma_unmap_sg(nandc->dev, desc->bam_sgl,
>> +				     desc->sgl_cnt, desc->dir);
>> +		else
>> +			dma_unmap_sg(nandc->dev, &desc->sgl, 1,
>> +				     desc->dir);
>> +
>>   		kfree(desc);
>>   	}
>>   }
>> 

-- 
Abhishek Sahu