linux-kernel - Re: [PATCH] dmaengine: of_dma: approximate an average distribution

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Date:	Wed, 11 May 2016 15:49:25 +0200
From:	"Niklas Söderlund" <niklas.soderlund@...natech.se>
To:	dan.j.williams@...el.com, vinod.koul@...el.com,
	dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org,
	arnd@...db.de
Cc:	linux-renesas-soc@...r.kernel.org
Subject: Re: [PATCH] dmaengine: of_dma: approximate an average distribution

In my haste I forgot the most important part of this patch, I'm sorry 
Arnd.

Suggested-by: Arnd Bergmann <arnd@...db.de>

On 2016-05-11 15:15:11 +0200, Niklas Söderlund wrote:
> Currently the following DT description would result in dmac0 always
> being tried first and dmac1 second if dmac0 was unavailable. This
> results in heavier use of dmac0 then of dmac1. This patch adds an
> approximate average distribution over the two nodes lessening the load
> of anyone of them.
> 
>    i2c6: i2c@...b0000 {
>            ...
>            dmas = <&dmac0 0x77>, <&dmac0 0x78>,
>                   <&dmac1 0x77>, <&dmac1 0x78>;
>            dma-names = "tx", "rx", "tx", "rx";
>            ...
>    };
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@...natech.se>
> ---
>  drivers/dma/of-dma.c | 12 ++++++++++--
>  1 file changed, 10 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/of-dma.c b/drivers/dma/of-dma.c
> index 1e1f298..faae0bf 100644
> --- a/drivers/dma/of-dma.c
> +++ b/drivers/dma/of-dma.c
> @@ -240,8 +240,9 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  	struct of_phandle_args	dma_spec;
>  	struct of_dma		*ofdma;
>  	struct dma_chan		*chan;
> -	int			count, i;
> +	int			count, i, start;
>  	int			ret_no_channel = -ENODEV;
> +	static atomic_t		last_index;
>  
>  	if (!np || !name) {
>  		pr_err("%s: not enough information provided\n", __func__);
> @@ -259,8 +260,15 @@ struct dma_chan *of_dma_request_slave_channel(struct device_node *np,
>  		return ERR_PTR(-ENODEV);
>  	}
>  
> +	/*
> +	 * approximate an average distribution across multiple
> +	 * entries with the same name
> +	 */
> +	start = atomic_inc_return(&last_index);
>  	for (i = 0; i < count; i++) {
> -		if (of_dma_match_channel(np, name, i, &dma_spec))
> +		if (of_dma_match_channel(np, name,
> +					 (i + start) % count,
> +					 &dma_spec))
>  			continue;
>  
>  		mutex_lock(&of_dma_lock);
> -- 
> 2.8.2
> 

-- 
Regards,
Niklas Söderlund