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

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Message-ID: <30d8bd45-4e5d-3703-5f41-07f5fc70f09d@microchip.com>
Date:   Thu, 29 Mar 2018 16:20:38 +0200
From:   Nicolas Ferre <nicolas.ferre@...rochip.com>
To:     Peter Rosin <peda@...ntia.se>, <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 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?

Best regards,
   Nicoals

>   enum atmel_nand_rb_type {
>   	ATMEL_NAND_NO_RB,
>   	ATMEL_NAND_NATIVE_RB,
> @@ -1977,7 +1982,7 @@ static int atmel_nand_controller_init(struct atmel_nand_controller *nc,
>   		return ret;
>   	}
>   
> -	if (nc->caps->has_dma) {
> +	if (nc->caps->has_dma && !atmel_nand_avoid_dma) {
>   		dma_cap_mask_t mask;
>   
>   		dma_cap_zero(mask);
> 


-- 
Nicolas Ferre