linux-kernel - Re: [PATCH] dmaengine: implement pause and resume for dw

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Date:	Tue, 19 Apr 2011 10:59:09 +0530
From:	viresh kumar <viresh.kumar@...com>
To:	Linus Walleij <linus.walleij@...aro.org>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Vinod Koul <vinod.koul@...el.com>,
	Dan Williams <dan.j.williams@...el.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	amitgoel <amit.goel@...com>,
	Armando VISCONTI <armando.visconti@...com>,
	Shiraz HASHIM <shiraz.hashim@...com>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"viresh.linux@...il.com" <viresh.linux@...il.com>
Subject: Re: [PATCH] dmaengine: implement pause and resume for dw_dmac

On 04/19/2011 06:01 AM, Linus Walleij wrote:
> It seems that the SPEAr needs this.
> 
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>

Thanks for sending this.
Actually i wasn't sure that disabling channel will simply pause it, and not
finish the transfer. So, didn't went for this change.

> ---
>  drivers/dma/dw_dmac.c      |   22 ++++++++++++++++++++--
>  drivers/dma/dw_dmac_regs.h |    1 +
>  2 files changed, 21 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> index 9c25c7d..60ac779 100644
> --- a/drivers/dma/dw_dmac.c
> +++ b/drivers/dma/dw_dmac.c
> @@ -801,8 +801,7 @@ static int dwc_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
>  	struct dw_desc		*desc, *_desc;
>  	LIST_HEAD(list);
>  
> -	/* Only supports DMA_TERMINATE_ALL */
> -	if (cmd != DMA_TERMINATE_ALL)
> +	if (cmd != DMA_TERMINATE_ALL && cmd != DMA_PAUSE && cmd != DMA_RESUME)
>  		return -ENXIO;
>  
>  	/*
> @@ -813,11 +812,30 @@ static int dwc_control(struct dma_chan *chan, enum dma_ctrl_cmd cmd,
>  	 */
>  	spin_lock_bh(&dwc->lock);
>  
> +	if (cmd == DMA_RESUME) {
> +		if (dwc->paused) {
> +			channel_set_bit(dw, CH_EN, dwc->mask);
> +			while (!dma_readl(dw, CH_EN) & dwc->mask)

Probably should be written as
			while (!(dma_readl(dw, CH_EN) & dwc->mask))

> +				cpu_relax();
> +		}

Should return error in else part??

> +		spin_unlock_bh(&dwc->lock);
> +		return 0;
> +	}
> +
>  	channel_clear_bit(dw, CH_EN, dwc->mask);
>  
>  	while (dma_readl(dw, CH_EN) & dwc->mask)
>  		cpu_relax();
>  
> +	if (cmd == DMA_PAUSE) {
> +		dwc->paused = true;
> +		spin_unlock_bh(&dwc->lock);

I have sent another patchset in which _bh variants are replaced with irqsave
variants. To remove any conflicts, i would add your patch in my patchset, with
above mentioned changes keeping your authorship intact.

Will that be fine??

-- 
viresh
--
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