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

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Date:	Thu, 15 Oct 2015 12:12:29 -0500
From:	"Franklin S Cooper Jr." <fcooper@...com>
To:	Roger Quadros <rogerq@...com>
CC:	<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>, Tony Lindgren <tony@...mide.com>
Subject: Re: [PATCH 1/5] mtd: nand: omap2: Support parsing dma channel
 information from DT



On 10/15/2015 02:35 AM, Roger Quadros wrote:
> On 14/10/15 23:03, Franklin S Cooper Jr. wrote:
>>
>> 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.
> In that case the dma information must be in the GPMC node.
Ok I'll be sending a v2 patchset soon but I'll be leaving this as is.
>
> cheers,
> -roger

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