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

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Date:   Tue, 29 May 2018 09:10:42 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Eugen Hristev <eugen.hristev@...rochip.com>
Cc:     Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        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
Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using
 dma

On 2018-05-29 08:30, Eugen Hristev wrote:
> 
> 
> On 28.05.2018 13:10, Peter Rosin wrote:
>> On 2018-05-28 00:11, Peter Rosin wrote:
>>> 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...
> 
>  >> [...]
> 
>>> 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...
> 
> Hello Peter,
> 
> Thank you for all the information, I will chip in to help a little bit.
> The Master/channel is described in the device tree. The channel has a 
> controller, a mem/periph interface and a periph ID, plus a FIFO 
> configuration.
> 
> The dma chan number reported in the dmesg is just software.

Got that, that was why I added the various additional traces in that
horrid patch in the mail you are responding to :-)

>                                                             Here is an 
> example from DT:
> dmas = <&dma0 2 AT91_DMA_CFG_PER_ID(1)>,
>         <&dma0 2 AT91_DMA_CFG_PER_ID(2)>;
> 
> you can match this with the help from 
> Documentation/devicetree/bindings/dma/atmel-dma.txt:
> 
> 1. A phandle pointing to the DMA controller. 
> 
> 2. The memory interface (16 most significant bits), the peripheral 
> interface
> (16 less significant bits). 
> 
> 3. Parameters for the at91 DMA configuration register which are device 
> 
> dependent: 
> 
>    - bit 7-0: peripheral identifier for the hardware handshaking 
> interface. The
>    identifier can be different for tx and rx. 
> 
>    - bit 11-8: FIFO configuration. 0 for half FIFO, 1 for ALAP, 2 for ASAP.
> 
> 
> So , what was Tudor asking for, is your DT for the ebi node (if you are 
> using ebi), or, your NFC SRAM (Nand Flash Controller SRAM) DMA 
> devicetree chunk, so, we can figure out which type of DMA are you using.
> 
> Normally, the ebi should be connected to both DMA0 and DMA1 on those 
> interfaces specified in DT. Which ones you want to use, depends on your 
> setup (and contention on the bus/accesses, like in your case, the HLCDC)
> 
> Thats why we have multiple choices, to pick the right one for each case.
> In our vanilla DT sama5d3.dtsi we do not have DMA described for ebi 
> interface.

Ahh, *that* NAND DMA configuration. Of course, how silly of me...

This is a setup based on the at91-linea.dtsi "CPU" board. That dtsi should
have the relevant NAND/DMA info. Also, at91-nattis-2-natte-2.dts describes
the older HW (with a 1024x768 panel) that is also affected, if you want a
full device tree to look at.

Looks like I didn't make a selection, quoting from at91-linea.dtsi:

&ebi {
	pinctrl-0 = <&pinctrl_ebi_nand_addr>;
	pinctrl-names = "default";
	status = "okay";
};

&nand_controller {
	status = "okay";

	nand: nand@3 {
		reg = <0x3 0x0 0x2>;
		atmel,rb = <0>;
		nand-bus-width = <8>;
		nand-ecc-mode = "hw";
		nand-ecc-strength = <4>;
		nand-ecc-step-size = <512>;
		nand-on-flash-bbt;
		label = "atmel_nand";
	};
};

The reason is probably because the sama5d3xek device-trees didn't at the
time of "fork". Does anybody have any suggestion for some extra properties
to try in the above nodes?

Further, I forgot that I had actually upstreamed linea support for
at91bootstrap, so relevant NAND timings etc can be found in lpddr1_init()
in

	at91bootstrap/contrib/board/axentia/sama5d3_linea/sama5d3_linea.c

Cheers,
Peter