linux-kernel - Re: [PATCH v4 2/6] dmaengine: Add dma_chan_is_in

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Message-ID: <20080702095940.699fe704@hskinnemo-gx745.norway.atmel.com>
Date:	Wed, 2 Jul 2008 09:59:40 +0200
From:	Haavard Skinnemoen <haavard.skinnemoen@...el.com>
To:	"Dan Williams" <dan.j.williams@...el.com>
Cc:	"Pierre Ossman" <drzeus-list@...eus.cx>,
	linux-kernel@...r.kernel.org, linux-embedded@...r.kernel.org,
	kernel@...32linux.org, shannon.nelson@...el.com,
	"David Brownell" <david-b@...bell.net>
Subject: Re: [PATCH v4 2/6] dmaengine: Add dma_chan_is_in_use() function

"Dan Williams" <dan.j.williams@...el.com> wrote:
> Actually we will probably need something like the following.
> ->client_count is protected by the dma_list_mutex.  
> 
> diff --git a/drivers/dma/dmaengine.c b/drivers/dma/dmaengine.c
> index 99c22b4..10de69e 100644
> --- a/drivers/dma/dmaengine.c
> +++ b/drivers/dma/dmaengine.c
> @@ -183,9 +183,10 @@ static void dma_client_chan_alloc(struct
> dma_client *client)
>  				/* we are done once this client rejects
>  				 * an available resource
>  				 */
> -				if (ack == DMA_ACK)
> +				if (ack == DMA_ACK) {
>  					dma_chan_get(chan);
> -				else if (ack == DMA_NAK)
> +					chan->client_count++;
> +				} else if (ack == DMA_NAK)
>  					return;
>  			}

This looks good to me. I can use client_count to determine if dwc->dws
is actually valid so that channels that were initially allocated for a
slave but NAK'ed or DUP'ed can be reclaimed for other purposes.

It still doesn't solve the issue with memory wastage, but we probably
shouldn't expect to keep a lot of unused channels around anyway.

Thanks!

Haavard
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