linux-kernel - Re: [PATCH] dmaengine/coh901318: fix slave submission semantics

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Date:	Thu, 07 Jul 2011 07:39:46 +0530
From:	Vinod Koul <vkoul@...radead.org>
To:	Linus Walleij <linus.walleij@...ricsson.com>
Cc:	linux-kernel@...r.kernel.org,
	Dan Williams <dan.j.williams@...el.com>,
	Lee Jones <lee.jones@...aro.org>,
	Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [PATCH] dmaengine/coh901318: fix slave submission semantics

On Fri, 2011-07-01 at 16:47 +0200, Linus Walleij wrote:
> From: Linus Walleij <linus.walleij@...aro.org>
> 
> While testing Per Forlins MMC speed improvements I noticed a
> semantic bug in the COH901318 driver: it will write to channel
> registers in the prep_slave_sg() function, instead of deferring
> it to later, breaking the assumption from the drivers to be able
> to queue up new jobs while another job is running. Fix this by
> storing up the initial register writes in the job descriptors
> and write them to hardware when we process the descriptor
> instead. Now the stress tests work.
> 
> Acked-by: Per Forlin <per.forlin@...aro.org>
> Signed-off-by: Linus Walleij <linus.walleij@...aro.org>
> ---
Looks good, it is in my queue...

>  drivers/dma/coh901318.c |   19 ++++++++++++-------
>  1 files changed, 12 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma/coh901318.c b/drivers/dma/coh901318.c
> index af8c0b5..a7fca16 100644
> --- a/drivers/dma/coh901318.c
> +++ b/drivers/dma/coh901318.c
> @@ -40,6 +40,8 @@ struct coh901318_desc {
>  	struct coh901318_lli *lli;
>  	enum dma_data_direction dir;
>  	unsigned long flags;
> +	u32 head_config;
> +	u32 head_ctrl;
>  };
>  
>  struct coh901318_base {
> @@ -660,6 +662,9 @@ static struct coh901318_desc *coh901318_queue_start(struct coh901318_chan *cohc)
>  
>  		coh901318_desc_submit(cohc, cohd);
>  
> +		/* Program the transaction head */
> +		coh901318_set_conf(cohc, cohd->head_config);
> +		coh901318_set_ctrl(cohc, cohd->head_ctrl);
>  		coh901318_prep_linked_list(cohc, cohd->lli);
>  
>  		/* start dma job on this channel */
> @@ -1090,8 +1095,6 @@ coh901318_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  	} else
>  		goto err_direction;
>  
> -	coh901318_set_conf(cohc, config);
> -
>  	/* The dma only supports transmitting packages up to
>  	 * MAX_DMA_PACKET_SIZE. Calculate to total number of
>  	 * dma elemts required to send the entire sg list
> @@ -1128,16 +1131,18 @@ coh901318_prep_slave_sg(struct dma_chan *chan, struct scatterlist *sgl,
>  	if (ret)
>  		goto err_lli_fill;
>  
> -	/*
> -	 * Set the default ctrl for the channel to the one from the lli,
> -	 * things may have changed due to odd buffer alignment etc.
> -	 */
> -	coh901318_set_ctrl(cohc, lli->control);
>  
>  	COH_DBG(coh901318_list_print(cohc, lli));
>  
>  	/* Pick a descriptor to handle this transfer */
>  	cohd = coh901318_desc_get(cohc);
> +	cohd->head_config = config;
> +	/*
> +	 * Set the default head ctrl for the channel to the one from the
> +	 * lli, things may have changed due to odd buffer alignment
> +	 * etc.
> +	 */
> +	cohd->head_ctrl = lli->control;
>  	cohd->dir = direction;
>  	cohd->flags = flags;
>  	cohd->desc.tx_submit = coh901318_tx_submit;

-- 
~Vinod Koul
Intel Corp.

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