linux-kernel - Re: [PATCH v2 0/2] Add memcpy support for tegra210-adma

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Date:   Tue, 6 Sep 2016 14:46:01 +0100
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>, <vinod.koul@...el.com>
CC:     <linux-kernel@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <dmaengine@...r.kernel.org>, <gnurou@...il.com>,
        <thierry.reding@...il.com>, <swarren@...dotorg.org>,
        <ldewangan@...dia.com>
Subject: Re: [PATCH v2 0/2] Add memcpy support for tegra210-adma


On 06/09/16 14:04, Jon Hunter wrote:
> 
> On 06/09/16 13:03, Dmitry Osipenko wrote:
>> On 06.09.2016 14:33, Jon Hunter wrote:
>>>
>>> On 03/09/16 01:32, Nicolin Chen wrote:
>>>> This series of patches add memcpy support for tegra210 ADMA engine.
>>>
>>> Thanks. Any reason you choose this DMA and not the APB DMA? The APB DMA
>>> is more of a generic DMA and so for memcpy it would seem to be a good
>>> choice and it is available on all Tegras not just Tegra210.
>>>
>>
>> Just a small clarification:
>>
>> If I'm not mistaken, APB DMA is mem-to-device, while AHB DMA is mem-to-mem. So,
>> you probably meant AHB and not the APB.
> 
> Description from the Tegra TRM:
> 
> "The APB DMA Controller is placed between the AHB Bus and the APB Bus
> and is a master on both buses.
> 
> The APB DMA Controller is used for block data transfers from a source
> location to the destination location. The source may be
> DRAM or IRAM, and the destination location could be devices placed on
> APB Bus; or vice versa."

Sorry this appears to be a completely worthless response :-(

I had made the assumption that if the DMA can transfer from APB-to-AHB
and AHB-to-APB, it could also do AHB to AHB. However, now I look closely
at the registers I see that it cannot and therefore, cannot support
memcpy at all! Ok, so ignore my comment here, as it appears only the
ADMA can support memcpy. Weird.

Jon

-- 
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