linux-kernel - Re: [PATCHv3] DMAEngine: Define interleaved transfer request api

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Date:	Tue, 20 Sep 2011 23:38:59 +0530
From:	Jassi Brar <jaswinder.singh@...aro.org>
To:	Vinod Koul <vinod.koul@...el.com>
Cc:	dan.j.williams@...el.com, linux-kernel@...r.kernel.org,
	rmk@....linux.org.uk, 21cnbao@...il.com
Subject: Re: [PATCHv3] DMAEngine: Define interleaved transfer request api

On 20 September 2011 22:22, Vinod Koul <vinod.koul@...el.com> wrote:
>>  /**
>>   * enum dma_ctrl_flags - DMA flags to augment operation preparation,
>> @@ -309,6 +376,8 @@ typedef void (*dma_async_tx_callback)(void *dma_async_param);
>>   * @chan: target channel for this operation
>>   * @tx_submit: set the prepared descriptor(s) to be executed by the engine
>>   * @callback: routine to call after this operation is complete
>> + *   And after each frame if the 'frm_irq' flag is set during
>> + *   device_prep_interleaved_dma.
> Nope, if callback is set it should be called
What makes you think it won't be called? Note that it starts with _AND_
'frm_irq' would only cause the callbacks done _additionally_ after each frame.

And no, DMA_PREP_INTERRUPT can't serve that purpose because that acts at
only the end of full transfer not a part of it.

> I think frm_irq is not required
Barry doesn't need it, so yes, I'd better remove it for now and make
my life easier.


> Also for slave transfers, how do we infer direction?
I already explained to Barry.  Here's it again.

At any time, the dmac driver knows if the channel, on which the xfer is
prepared/submitted is Slave or not.

SLAVE Transfer
   dmaxfer_template.src_inc  && !dmaxfer_template.dst_inc  => DMA_TO_DEVICE
   !dmaxfer_template.src_inc  && dmaxfer_template.dst_inc  => DMA_FROM_DEVICE

Mem->Mem Transfer
   dmaxfer_template.src_inc  && !dmaxfer_template.dst_inc  => Meaningless
   !dmaxfer_template.src_inc  && dmaxfer_template.dst_inc  => MemSet
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