linux-kernel - Re: [PATCH] dmaengine: delete redundant chan_id and chancnt initialization in dma drivers

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Date:	Thu, 22 Sep 2011 14:42:51 +0800
From:	Barry Song <21cnbao@...il.com>
To:	Jassi Brar <jassisinghbrar@...il.com>
Cc:	Barry Song <Baohua.Song@....com>,
	Piotr Ziecik <kosmo@...ihalf.com>,
	Vinod Koul <vinod.koul@...el.com>,
	Pelagicore AB <info@...agicore.com>,
	Nicolas Ferre <nicolas.ferre@...el.com>,
	linux-kernel@...r.kernel.org, Yong Wang <yong.y.wang@...el.com>,
	dan.j.williams@...el.com, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] dmaengine: delete redundant chan_id and chancnt
 initialization in dma drivers

2011/9/22 Jassi Brar <jassisinghbrar@...il.com>:
> On Thu, Sep 22, 2011 at 12:01 PM, Barry Song <21cnbao@...il.com> wrote:
>> 2011/9/22 Jassi Brar <jassisinghbrar@...il.com>:
>>> On Thu, Sep 22, 2011 at 11:11 AM, Jassi Brar <jassisinghbrar@...il.com> wrote:
>>>>
>>>>> client drivers can request a specific chan_id just like it can request a gpio.
>>>> No dear. That's not gonna fly if we are to have common client drivers
>>>> across SoCs.
>>>>
>>> Btw, I meant you can't simply have clients specify a channel number and
>>> get the channel in a portable manner. Clients need to specify the capabilities
>>> they need of the channel.
>>
>> if the dmac is flexible in design, what you said is right. but the
>> problem is that there are some chips which actually fix one channel to
>> one peripheral.
> Nevertheless it is better to assume the dmac's req-signals could be hacked
> to re-route at even runtime.
> Also it won't work for client drivers that run the same controller on different
> SoC with a different dmac.
>
you mean there is a mapping table in dmac driver. otherwise, there
will always require some changes in client drivers.
-barry
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