linux-kernel - Re: [RFC PATCH] tty/serial: atmel

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Date:	Tue, 11 Oct 2011 18:04:51 +0200
From:	Nicolas Ferre <nicolas.ferre@...el.com>
To:	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <robherring2@...il.com>
CC:	linux-arm-kernel@...ts.infradead.org, alan@...ux.intel.com,
	linux-serial@...r.kernel.org, devicetree-discuss@...ts.ozlabs.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] tty/serial: atmel_serial: add device tree support

On 10/04/2011 06:55 PM, Grant Likely :
> On Tue, Oct 04, 2011 at 08:08:27AM -0500, Rob Herring wrote:
>> Nicolas,
>>
>> On 10/04/2011 03:18 AM, Nicolas Ferre wrote:
>>> On 10/04/2011 03:58 AM, Rob Herring :
>>>> On 10/03/2011 04:51 AM, Nicolas Ferre wrote:
>>>>> +Optional properties:
>>>>> +- atmel,use-dma-rx: use of PDC or DMA for receiving data
>>>>> +- atmel,use-dma-tx: use of PDC or DMA for transmitting data
>>>>
>>>> Is this an internal DMA or separate DMA controller? If the latter, these
>>>> should be phandles to a DMA channel/request.
>>>
>>> Well, for now it relies on PDC (looks like an internal DMA). There is no
>>> notion of channel/request so I think it is appropriate to keep it like this.
>>>
>>
>> Okay. Although, this is a bit of Linux creeping into DT. DT should
>> describe the h/w. You should really be describing whether the h/w
>> supports DMA or not rather than whether you want to use DMA or not.
>> Since DMA support is really tied to the SOC rather than board, you could
>> just use the compatible string to distinguish platforms that support DMA
>> or not. So what is determining this setting? Is it purely user choice?
> 
> It is okay for a binding to still requires config properties like this
> to state if the DMA can be used, even if compatible is enough to
> distinquish.  However, you're right to bring it up.  It is a design
> choice that should be made thoughtfully.

Grant, Rob,

Thanks for your inputs.

I would like to keep this binding to allow the user to choose the way he
likes to use integrated DMA.

I plan to resend a patch series about this serial driver once I will be
able to propose a rs485 binding.

Cheers,
-- 
Nicolas Ferre
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