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

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Message-ID: <20180402223232.6213f409@bbrezillon>
Date:   Mon, 2 Apr 2018 22:32:32 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Peter Rosin <peda@...ntia.se>
Cc:     Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Richard Weinberger <richard@....at>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        linux-kernel@...r.kernel.org, Marek Vasut <marek.vasut@...il.com>,
        linux-mtd@...ts.infradead.org, Josh Wu <rainyfeeling@...look.com>,
        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 Mon, 2 Apr 2018 22:20:20 +0200
Boris Brezillon <boris.brezillon@...tlin.com> wrote:

> >   
> > > And
> > > which DDR slave is the target? 7, 8, 9 or 10? More than one?    
> > 
> > This, I don't know. I guess all of them can be used.  
> 
> Looks like I was wrong. According to "Table 15-3. SAMA5D3 Master to
> Slave Access", LCDC port 0 can only access DDR port 2 and LCDC port 1
> can only access DDR port 3.
> 
> Can you try to write 0x3 to 0xFFFFECCC and 0x30 to 0xFFFFECD4?
> 

Oh, one more thing. Changing the priority won't necessarily solve your
problem because of that:

"
If more than one master requests the slave bus, regardless of the
respective masters priorities, no master will be granted
the slave bus for two consecutive runs. A master can only get
back-to-back grants so long as it is the only requesting
master.
"

To solve that, you'll have to play with MATRIX_MCFGy.ULBT (make sure
DMAC0 and DMAC1 have a small enough ULBT that is not 0) or
MATRIX_SCFGx.SLOT_CYCLE (that one is probably harder to get right
since it's expressed in AHB clock cycles).

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