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

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Message-ID: <20151014181337.GF10113@atomide.com>
Date:	Wed, 14 Oct 2015 11:13:38 -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 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 :)

Regards,

Tony
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