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

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Date:   Thu, 29 Mar 2018 16:23:32 +0200
From:   Peter Rosin <peda@...ntia.se>
To:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        linux-kernel@...r.kernel.org,
        Boris Brezillon <boris.brezillon@...tlin.com>
Cc:     "wenyouya@...il.com" <wenyouya@...il.com>,
        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>,
        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 16:20, Nicolas Ferre wrote:
> On 29/03/2018 at 15:10, Peter Rosin 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);
> 
> We had the DT parameter "atmel,nand-has-dma" for this purpose and it was 
> associated with a module parameter as well (use_dma,).
> 
> Is it only managed by old DT binding?

Saw it, but I need the reverse. I.e. *not* using DMA.

And I didn't think this belonged in DT since in some sense it doesn't really
describe HW so I went with a module parameter.

Cheers,
Peter