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SubjectRe: [PATCH 07/13] dmaengine: introduce dma_request_channel and private channels
On Fri, Dec 12, 2008 at 7:29 AM, Sosnowski, Maciej
<maciej.sosnowski@intel.com> wrote:
>> clear_bit(DMA_INTERRUPT, dma_cap_mask_all.bits);
>> + clear_bit(DMA_PRIVATE, dma_cap_mask_all.bits);
>> clear_bit(DMA_SLAVE, dma_cap_mask_all.bits);
>
> The comment above should be updated according to this change:
> -/* 'interrupt' and 'slave' are channel capabilities, but are not
> +/* 'interrupt', 'private' and 'slave' are channel capabilities, but are not
>

ok.

>> +static struct dma_chan *private_candidate(dma_cap_mask_t *mask,
>> struct dma_device *dev) +{
>> + struct dma_chan *chan;
>> + struct dma_chan *ret = NULL;
>> +
>> + /* devices with multiple channels need special handling as we need
>> to + * ensure that all channels are either private or public.
>> + */
>> + if (dev->chancnt > 1 && !dma_has_cap(DMA_PRIVATE, dev->cap_mask))
>> + list_for_each_entry(chan, &dev->channels, device_node) {
>> + /* some channels are already publicly allocated */
>> + if (chan->client_count)
>> + return NULL;
>> + }
>
> Isn't it a dangerous approach to let clients consume for their exclusive usage channels
> meant for general-purpose ("pubilc" ones)?
> Why not to limit private_candidate to devices with DMA_PRIVATE capability only?
>

This allows unused channels to be claimed by dma_request_channel().
It is not dangerous as long as ->client_count is zero.

>> +
>> + list_for_each_entry(chan, &dev->channels, device_node) {
>> + if (!__dma_chan_satisfies_mask(chan, mask)) {
>> + pr_debug("%s: %s wrong capabilities\n",
>> + __func__, dev_name(&chan->dev));
>> + continue;
>> + }
>
> As capabilities are per device, this check could be performed just once
> before list_for_each_entry(chan, &dev->channels, device_node).
>

Yes, changed.

Thanks,
Dan


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