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

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Date:   Thu, 29 Mar 2018 16:27:12 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     linux-kernel@...r.kernel.org, Josh Wu <rainyfeeling@...look.com>,
        Richard Weinberger <richard@....at>,
        David Woodhouse <dwmw2@...radead.org>,
        Brian Norris <computersforpeace@...il.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-mtd@...ts.infradead.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] mtd: nand: raw: atmel: add module param to avoid using
 dma

On 2018-03-29 15:44, Boris Brezillon wrote:
> On Thu, 29 Mar 2018 15:37:43 +0200
> Peter Rosin <peda@...ntia.se> wrote:
> 
>> On 2018-03-29 15:33, Boris Brezillon wrote:
>>> On Thu, 29 Mar 2018 15:10:54 +0200
>>> Peter Rosin <peda@...ntia.se> wrote:
>>>   
>>>> On a sama5d31 with a Full-HD dual LVDS panel (132MHz pixel clock) NAND
>>>> flash accesses have a tendency to cause display disturbances. Add a
>>>> module param to disable DMA from the NAND controller, since that fixes
>>>> the display problem for me.
>>>>
>>>> Signed-off-by: Peter Rosin <peda@...ntia.se>
>>>> ---
>>>>  drivers/mtd/nand/raw/atmel/nand-controller.c | 7 ++++++-
>>>>  1 file changed, 6 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/drivers/mtd/nand/raw/atmel/nand-controller.c b/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>> index b2f00b398490..2ff7a77c7b8e 100644
>>>> --- a/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>> +++ b/drivers/mtd/nand/raw/atmel/nand-controller.c
>>>> @@ -129,6 +129,11 @@
>>>>  #define DEFAULT_TIMEOUT_MS			1000
>>>>  #define MIN_DMA_LEN				128
>>>>  
>>>> +static bool atmel_nand_avoid_dma __read_mostly;
>>>> +
>>>> +MODULE_PARM_DESC(avoiddma, "Avoid using DMA");
>>>> +module_param_named(avoiddma, atmel_nand_avoid_dma, bool, 0400);  
>>>
>>> I'm not a big fan of those driver specific cmdline parameters. Can't we
>>> instead give an higher priority to HLCDC master using the bus matrix?  
>>
>> I don't know if it will be enough, but we sure can try. However, I have
>> no idea how to do that. I will happily test stuff though...
> 
> There's no interface to configure that from Linux, but you can try to
> tweak it with devmem and if that does the trick, maybe we can expose a
> way to configure that from Linux. For more details, see the "Bus Matrix
> (MATRIX)" section in Atmel datasheets.

I don't seem to succeed in changing the registers I think I need to change.
I can poke the "Write Protection Mode Register" by writing MAT0 and MAT1 to
it. But when I try to write to "Priority Registers B For Slaves" it doesn't
take, regardless of write protect mode.

Can the relevant bits only be written when the HLCDC is inactive or
something?

Cheers,
Peter