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

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Message-ID: <20180529171555.19dd723f@bbrezillon>
Date:   Tue, 29 May 2018 17:15:55 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Eugen Hristev <eugen.hristev@...rochip.com>
Cc:     Peter Rosin <peda@...ntia.se>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Josh Wu <rainyfeeling@...look.com>,
        Cyrille Pitchen <cyrille.pitchen@...ev4u.fr>,
        <linux-kernel@...r.kernel.org>, <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 Tue, 29 May 2018 18:01:40 +0300
Eugen Hristev <eugen.hristev@...rochip.com> wrote:

> [...]
> 
> 
> > 
> > I think you're missing something here. We use the DMA engine in memcpy
> > mode (SRAM -> DRAM), not in device mode (dev -> DRAM or DRAM -> dev).
> > So there's no dmas prop defined in the DT and there should not be.
> > 
> > Regards,
> > 
> > Boris
> >   
> 
> Ok, so the memcpy SRAM <-> DRAM will hog the transfer between DRAM and 
> LCD if my understanding is correct. That's the DMA that Peter wants to 
> disable with his patch ?
> 
> Then we can then try to force NFC SRAM DMA channels to use just DDR port 
> 1 or 2 for memcpy ?

You mean the dmaengine? According to "14.1.3 Master to Slave Access"
that's already the case.

Only DMAC0 can access the NFC SRAM and it's done through DMAC0:IF0,
then access to DDR is going through port DDR port 1 (DMAC0:IF1) or 2
(DMAC0:IF0).

> 
> I have also received a suggestion to try to increase the porches in 
> LCDC_LCDCFG3 .

Yep, Nicolas suggested something similar. Peter, can you try that?