linux-kernel - Re: [PATCH 07/13] dmaengine: introduce dma_request

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Message-ID: <e9c3a7c20812180927q7488f8b9n9641cf313363fcc5@mail.gmail.com>
Date:	Thu, 18 Dec 2008 10:27:56 -0700
From:	"Dan Williams" <dan.j.williams@...el.com>
To:	"Sosnowski, Maciej" <maciej.sosnowski@...el.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"hskinnemoen@...el.com" <hskinnemoen@...el.com>,
	"g.liakhovetski@....de" <g.liakhovetski@....de>,
	"nicolas.ferre@...el.com" <nicolas.ferre@...el.com>
Subject: Re: [PATCH 07/13] dmaengine: introduce dma_request_channel and private channels

On Thu, Dec 18, 2008 at 7:33 AM, Sosnowski, Maciej
<maciej.sosnowski@...el.com> wrote:
> What about situation, where some or all "public" channels in the system
> have been claimed by one client for its exclusive usage
> before another client appears trying to use available "public" channels?
> Despite of presence in the system of channels that supposed to be "public",
> the second cilent realizes that the channels are not available anymore at all
> or at least limited...
> Doesn't it contradict the general idea of "public" (general purpose) channels?
>

If a greedy module comes along and grabs all the channels via
dma_request_channel() then yes, there will be nothing left for the
public pool.  So, there is a requirement to "play nice".  If this
becomes an issue in practice we could add a DMA_NO_PRIVATE flag to
reserve a channel for public-only usage.

Regards,
Dan
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