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

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Date:   Mon, 2 Apr 2018 14:22:49 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Josh Wu <rainyfeeling@...look.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        linux-kernel@...r.kernel.org,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Marek Vasut <marek.vasut@...il.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 Thu, 29 Mar 2018 16:27:12 +0200
Peter Rosin <peda@...ntia.se> wrote:

> 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.

You mean 0x4D415400, right? ("MAT0" != 0x4D415400).

> But when I try to write to "Priority Registers B For Slaves" it doesn't
> take, regardless of write protect mode.

Did you check MATRIX_WPSR after writing to MATRIX_PRXSY?

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

I don't know, but maybe Nicolas does.

-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com