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 09:18:13 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	"Franklin S Cooper Jr." <fcooper@...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

* 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?

Regards,

Tony
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