linux-kernel - Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

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Date:	Fri, 13 Mar 2009 23:16:59 +0900 (JST)
From:	Atsushi Nemoto <anemo@....ocn.ne.jp>
To:	dan.j.williams@...el.com
Cc:	linux-mips@...ux-mips.org, ralf@...ux-mips.org,
	linux-kernel@...r.kernel.org, haavard.skinnemoen@...el.com
Subject: Re: [PATCH 1/2] dmaengine: TXx9 Soc DMA Controller driver

On Fri, 13 Mar 2009 01:19:50 +0900 (JST), Atsushi Nemoto <anemo@....ocn.ne.jp> wrote:
> Subject: dmaengine: Use chan_id provided by DMA device driver
> From: Atsushi Nemoto <anemo@....ocn.ne.jp>
> 
> If chan_id was already given by the DMA device driver, use it.
> Otherwise assign an incremental number for each channels.
> 
> This allows the DMA device driver to reserve some channel ID numbers.
...
> @@ -663,7 +664,9 @@ int dma_async_device_register(struct dma_device *device)
>  			continue;
>  		}
>  
> -		chan->chan_id = chancnt++;
> +		if (!chan->chan_id)
> +			chan->chan_id = chan_id++;
> +		chancnt++;
>  		chan->dev->device.class = &dma_devclass;
>  		chan->dev->device.parent = device->dev;
>  		chan->dev->chan = chan;

This patch will fix another potential problem.  Some driver, for
example ipu, assumes chan_id is an index of its internal array.  But
dmaengine core does not guarantee it.

	/* represent channels in sysfs. Probably want devs too */
	list_for_each_entry(chan, &device->channels, device_node) {
		chan->local = alloc_percpu(typeof(*chan->local));
		if (chan->local == NULL)
			continue;
		chan->dev = kzalloc(sizeof(*chan->dev), GFP_KERNEL);
		if (chan->dev == NULL) {
			free_percpu(chan->local);
			continue;
		}

		chan->chan_id = chancnt++;
		...
	}
	device->chancnt = chancnt;

If alloc_percpu or kzalloc failed, chan_id does not match with its
position in device->channels list.


And above "continue" looks buggy anyway.  Keeping incomplete channels
in device->channels list looks very dangerous...

---
Atsushi Nemoto
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