linux-kernel - Re: [PATCH 07/12] i2c: qup: use the complete transfer length to choose DMA mode

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Date:   Fri, 16 Feb 2018 10:05:42 +0530
From:   Sricharan R <sricharan@...eaurora.org>
To:     Abhishek Sahu <absahu@...eaurora.org>,
        Andy Gross <andy.gross@...aro.org>,
        Wolfram Sang <wsa@...-dreams.de>
Cc:     David Brown <david.brown@...aro.org>,
        linux-arm-msm@...r.kernel.org, linux-soc@...r.kernel.org,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 07/12] i2c: qup: use the complete transfer length to
 choose DMA mode



On 2/3/2018 1:28 PM, Abhishek Sahu wrote:
> Currently each message length in complete transfer is being
> checked for determining DMA mode and if any of the message length
> is less than FIFO length then non DMA mode is being used which
> will increase overhead. DMA can be used for any length and it
> should be determined with complete transfer length. Now, this
> patch introduces DMA threshold length and the transfer will be
> done in DMA mode if the total length is greater than this
> threshold length.
> 
> Signed-off-by: Abhishek Sahu <absahu@...eaurora.org>
> ---
>  drivers/i2c/busses/i2c-qup.c | 15 +++++++++------
>  1 file changed, 9 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> index 6227a5c..a91fc70 100644
> --- a/drivers/i2c/busses/i2c-qup.c
> +++ b/drivers/i2c/busses/i2c-qup.c
> @@ -192,6 +192,8 @@ struct qup_i2c_dev {
>  	bool			is_dma;
>  	/* To check if the current transfer is using DMA */
>  	bool			use_dma;
> +	/* The threshold length above which DMA will be used */
> +	unsigned int		dma_threshold;
>  	struct			dma_pool *dpool;
>  	struct			qup_i2c_tag start_tag;
>  	struct			qup_i2c_bam brx;
> @@ -1294,7 +1296,8 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
>  			   int num)
>  {
>  	struct qup_i2c_dev *qup = i2c_get_adapdata(adap);
> -	int ret, len, idx = 0;
> +	int ret, idx = 0;
> +	unsigned int total_len = 0;
>  
>  	qup->bus_err = 0;
>  	qup->qup_err = 0;
> @@ -1320,14 +1323,13 @@ static int qup_i2c_xfer_v2(struct i2c_adapter *adap,
>  				goto out;
>  			}
>  
> -			len = (msgs[idx].len > qup->out_fifo_sz) ||
> -			      (msgs[idx].len > qup->in_fifo_sz);
> -
> -			if (is_vmalloc_addr(msgs[idx].buf) || !len)
> +			if (is_vmalloc_addr(msgs[idx].buf))
>  				break;
> +
> +			total_len += msgs[idx].len;
>  		}
>  
> -		if (idx == num)
> +		if (idx == num && total_len > qup->dma_threshold)
>  			qup->use_dma = true;
>  	}
>  
> @@ -1587,6 +1589,7 @@ static int qup_i2c_probe(struct platform_device *pdev)
>  
>  	size = QUP_INPUT_FIFO_SIZE(io_mode);
>  	qup->in_fifo_sz = qup->in_blk_sz * (2 << size);
> +	qup->dma_threshold = min(qup->out_fifo_sz, qup->in_fifo_sz);

  The patch is fine. small nit, you can avoid this global dma_threshold. Instead
  have it locally in qup_i2c_xfer_v2 itself.

Regards,
 Sricharan


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