linux-kernel - Re: [PATCH 2/2] dmaengine: omap-dma: Support for slave devices with data port window

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Date:   Mon, 14 Nov 2016 13:49:40 +0200
From:   Peter Ujfalusi <peter.ujfalusi@...com>
To:     Vinod Koul <vinod.koul@...el.com>
CC:     <dan.j.williams@...el.com>, Tony Lindgren <tony@...mide.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-omap@...r.kernel.org>, <arnd@...db.de>
Subject: Re: [PATCH 2/2] dmaengine: omap-dma: Support for slave devices with
 data port window

On 11/14/2016 12:55 PM, Vinod Koul wrote:
> On Mon, Nov 14, 2016 at 11:44:33AM +0200, Peter Ujfalusi wrote:
>> On 11/14/2016 06:35 AM, Vinod Koul wrote:
> 
>>>>  	} else {
>>>> -		d->ccr |= CCR_DST_AMODE_CONSTANT | CCR_SRC_AMODE_POSTINC;
>>>>  		d->csdp = CSDP_SRC_BURST_64 | CSDP_SRC_PACKED;
>>>> +
>>>> +		d->ccr |= CCR_SRC_AMODE_POSTINC;
>>>> +		if (port_window) {
>>>> +			d->ccr |= CCR_DST_AMODE_DBLIDX;
>>>> +
>>>> +			if (port_window / 64)
>>>> +				d->csdp = CSDP_DST_BURST_64 | CSDP_DST_PACKED;
>>>> +			else if (port_window / 32)
>>>> +				d->csdp = CSDP_DST_BURST_32 | CSDP_DST_PACKED;
>>>> +			else if (port_window / 16)
>>>> +				d->csdp = CSDP_DST_BURST_16 | CSDP_DST_PACKED;
>>>
>>> what does these mean?
>>
>> To optimize the speed on the write side. First check if the window size is
>> multiple of 64 bytes, we enable the 64byte burst and packed transfer, if not
>> try the 32bytes, then 16bytes.
>> Same for the opposite direction previously.
> 
> Ah and how does client know the size of window..?

Clients configuring the DMA should know what they are configuring for. If the
window size can be different they might have DT property if they need.

> 
>>
>>>
>>>> +		} else {
>>>> +			d->ccr |= CCR_DST_AMODE_CONSTANT;
>>>> +		}
>>>>  	}
>>>>  
>>>>  	d->cicr = CICR_DROP_IE | CICR_BLOCK_IE;
>>>> @@ -945,6 +979,9 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
>>>>  			d->ccr |= CCR_TRIGGER_SRC;
>>>>  
>>>>  		d->cicr |= CICR_MISALIGNED_ERR_IE | CICR_TRANS_ERR_IE;
>>>> +
>>>> +		if (port_window)
>>>> +			d->csdp |= CSDP_WRITE_LAST_NON_POSTED;
>>>>  	}
>>>>  	if (od->plat->errata & DMA_ERRATA_PARALLEL_CHANNELS)
>>>>  		d->clnk_ctrl = c->dma_ch;
>>>> @@ -970,6 +1007,10 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
>>>>  		osg->addr = sg_dma_address(sgent);
>>>>  		osg->en = en;
>>>>  		osg->fn = sg_dma_len(sgent) / frame_bytes;
>>>> +		if (port_window && dir == DMA_MEM_TO_DEV) {
>>>> +			osg->ei = 1;
>>>> +			osg->fi = (-1) * (port_window - 1);
>>>> +		}
>>>
>>> can you describe what you are trying here..
>>
>> The DMA is set up so one frame covers the port window. When the frame is
>> finished we need to start reading the next frame from the start of the window
>> again. The FI as (-1) * (port_window - 1) will take us to the start of the
>> window. When the frame is finished the DMA is pointing to the last byte of the
>> window.
> 
> Sound right to me, would help to add this as a comment..

OK, I will add a comment describing it.

> 


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