linux-kernel - Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using dma

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Date:   Mon, 28 May 2018 00:11:07 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Josh Wu <rainyfeeling@...look.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        linux-mtd@...ts.infradead.org, Richard Weinberger <richard@....at>,
        Brian Norris <computersforpeace@...il.com>,
        David Woodhouse <dwmw2@...radead.org>,
        linux-arm-kernel@...ts.infradead.org,
        Eugen Hristev <eugen.hristev@...rochip.com>
Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using
 dma

On 2018-05-27 11:18, Peter Rosin wrote:
> On 2018-05-25 16:51, Tudor Ambarus wrote:
>> We think the best way is to keep LCD on DDR Ports 2 and 3 (8th and 9th
>> slaves), to have maximum bandwidth and to use DMA on DDR port 1 for NAND
>> (7th slave).
> 
> Exactly how do I accomplish that?
> 
> I can see how I can move the LCD between slave DDR port 2 and 3 by
> selecting LCDC DMA master 8 or 9 (but according to the above it should
> not matter). The big question is how I control what slave the NAND flash
> is going to use? I find nothing in the datasheet, and the code is also
> non-transparent enough for me to figure it out by myself without
> throwing out this question first...

I added this:

diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c b/drivers/mtd/nand/raw/atmel/nand-controller.c
index e686fe73159e..3b33c63d2ed4 100644
--- a/drivers/mtd/nand/raw/atmel/nand-controller.c
+++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
@@ -1991,6 +1991,9 @@ static int atmel_nand_controller_init(struct atmel_nand_controller *nc,
 		nc->dmac = dma_request_channel(mask, NULL, NULL);
 		if (!nc->dmac)
 			dev_err(nc->dev, "Failed to request DMA channel\n");
+
+		dev_info(nc->dev, "using %s for DMA transfers\n",
+			 dma_chan_name(nc->dmac));
 	}
 
 	/* We do not retrieve the SMC syscon when parsing old DTs. */



and the output is

atmel-nand-controller 10000000.ebi:nand-controller: using dma0chan5 for DMA transfers

So, DMA controller 0 is in use. I still don't know if IF0, IF1 or IF2 is used
or how to find out. I guess IF2 is not in use since that does not allow any
DDR2 port as slave...

>From the datasheet, DMAC0/IF0 uses DDR2 Port 2, and DMAC0/IF1 uses DDR2 Port 1.
But, by the looks of the register content in my other mail, it seems as if
DMA0/IF1 can also use DDR2 Port 3.

So, I think I want either

A) the NAND controller to use DMAC0/IF0 (i.e. DDR2 port 1, and possibly 3) and
   the LCDC to use master 9 (i.e. DDR2 Port 2)

or

B) the NAND controller to use DMAC1/IF1 (i.e. DDR2 port 2) and the LCDC to use
   master 8 (i.e. DDR2 Port 3)

But, again, how do I limit DMAC0 to either of IF0 or IF1 for NAND accesses?

Note that I have previously tried to move LCDC DMA from master 8 (the default)
to master 9, and it got better, but not good enough. I.e. the visual glitches
remained, but were a little bit harder to trigger. That makes me suspect DMAC0
uses both IF0 and IF1 for its DMAs, but that it prefers IF0.

Cheers,
Peter