linux-kernel - Re: [RFC 2/4] dma: add dmaengine driver for Samsung s3c24xx SoCs

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Date:	Fri, 17 May 2013 14:20:49 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Heiko Stübner <heiko@...ech.de>
Cc:	Dan Williams <djbw@...com>, Vinod Koul <vinod.koul@...el.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	Kukjin Kim <kgene.kim@...sung.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>
Subject: Re: [RFC 2/4] dma: add dmaengine driver for Samsung s3c24xx SoCs

On Wed, May 15, 2013 at 10:31 PM, Heiko Stübner <heiko@...ech.de> wrote:

> If I understand the writel semantics and the thread from you from 2011 [0]
> correctly, only the writel to DMASKTRIG mustn't be relaxed to make sure the
> settings registers are written to before, so like:
>
>        writel_relaxed(txd->src_addr, phy->base + DISRC);
>        writel_relaxed(txd->disrcc, phy->base + DISRCC);
>        writel_relaxed(txd->dst_addr, phy->base + DIDST);
>        writel_relaxed(txd->didstc, phy->base + DIDSTC);
>        writel_relaxed(dcon, phy->base + DCON);
>
>        val = readl_relaxed(phy->base + DMASKTRIG);
>        val &= ~DMASKTRIG_STOP;
>        val |= DMASKTRIG_ON;
>        writel(val, phy->base + DMASKTRIG);

Yep. That will drain write buffers etc and make sure all outstanding writes hit
the hardware.

Yours,
Linus Walleij
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