linux-kernel - Re: [PATCH 1/5] mtd: nand: omap2: Support parsing dma channel information from DT

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Message-ID: <561E8184.6020206@ti.com>
Date:	Wed, 14 Oct 2015 11:23:32 -0500
From:	"Franklin S Cooper Jr." <fcooper@...com>
To:	Tony Lindgren <tony@...mide.com>
CC:	Roger Quadros <rogerq@...com>, <linux-kernel@...r.kernel.org>,
	<devicetree@...r.kernel.org>, <linux-omap@...r.kernel.org>,
	<linux-mtd@...ts.infradead.org>, <nsekhar@...com>,
	<computersforpeace@...il.com>, <dwmw2@...radead.org>
Subject: Re: [PATCH 1/5] mtd: nand: omap2: Support parsing dma channel
 information from DT



On 10/14/2015 11:18 AM, Tony Lindgren wrote:
> * Franklin S Cooper Jr. <fcooper@...com> [151014 07:37]:
>>
>> On 10/14/2015 09:11 AM, Roger Quadros wrote:
>>> On 14/10/15 16:26, Franklin S Cooper Jr. wrote:
>>>> On 10/14/2015 06:52 AM, Roger Quadros wrote:
>>>>> Franklin,
>>>>>
>>>>> On 14/10/15 14:36, Roger Quadros wrote:
>>>>>> On 13/10/15 04:38, Franklin S Cooper Jr wrote:
>>>>>>> Switch from dma_request_channel to allow passing dma channel
>>>>>>> information from DT rather than hardcoding a value.
>>>>>>>
>>>>>>> Signed-off-by: Franklin S Cooper Jr <fcooper@...com>
>>>>>> Acked-by: Roger Quadros <rogerq@...com>
>>>>>>
>>>>>>> ---
>>>>>>>  drivers/mtd/nand/omap2.c | 4 +++-
>>>>>>>  1 file changed, 3 insertions(+), 1 deletion(-)
>>>>>>>
>>>>>>> diff --git a/drivers/mtd/nand/omap2.c b/drivers/mtd/nand/omap2.c
>>>>>>> index d0f2620..957c32f 100644
>>>>>>> --- a/drivers/mtd/nand/omap2.c
>>>>>>> +++ b/drivers/mtd/nand/omap2.c
>>>>>>> @@ -1866,7 +1866,9 @@ static int omap_nand_probe(struct platform_device *pdev)
>>>>>>>  		dma_cap_zero(mask);
>>>>>>>  		dma_cap_set(DMA_SLAVE, mask);
>>>>>>>  		sig = OMAP24XX_DMA_GPMC;
>>>>>>> -		info->dma = dma_request_channel(mask, omap_dma_filter_fn, &sig);
>>>>>>> +		info->dma = dma_request_slave_channel_compat(mask,
>>>>>>> +			omap_dma_filter_fn, &sig, pdev->dev.parent, "rxtx");
>>>>>>> +
>>>>> Just discovered that you are using the parent device node.
>>>>>
>>>>> How about moving the dma bindings to the nand node instead and using
>>>>> pdev->dev here?
>>>> Roger,
>>>>
>>>> From what I can tell the interrupt number and the dma channel will always be
>>>> the same no matter what. Doesn't matter if you have multiple nands or a
>>>> combination of nands and nors. Since that is the case I think it just makes
>>>> sense to leave it in the gpmc parent node and define it once.
>>> Is prefetch/writepost dma used for NOR or any other GPMC peripheral
>>> or only for NAND?
>> The dma seems tied to the prefetch. From what I can tell the prefetch is only
>> used by nand.
>>> Let's also get Tony's inputs on this.
>> Sure.
> Hmm so what would keep other devices from using the prefetch
Looking at the TRM any references to the prefetch are always with respect to
NAND.

I also see the below mentioned in the TRM.
Pre-fetch and write posting engine associated with system DMA to get full performance from NAND
device with minimum impact on NOR/SRAM concurrent access.
>
> Regards,
>
> Tony

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