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

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Date:	Wed, 14 Oct 2015 15:03:07 -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 01:13 PM, Tony Lindgren wrote:
> * Franklin S Cooper Jr. <fcooper@...com> [151014 09:27]:
>>
>> 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.
> OK up to you guys to figure out if it may be usable in a generic way then :)
Ok I just got clarification from hw folks. DMA for GPMC can be used for any of the
various modes. But the prefetch is specific to NAND.
>
> Regards,
>
> Tony

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