linux-kernel - Re: [PATCH 2/2] dmaengine: omap-dma: Support for slave devices with data port window

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Date:   Mon, 14 Nov 2016 10:53:13 +0000
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Peter Ujfalusi <peter.ujfalusi@...com>
Cc:     vinod.koul@...el.com, dan.j.williams@...el.com,
        Tony Lindgren <tony@...mide.com>, dmaengine@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-omap@...r.kernel.org,
        arnd@...db.de
Subject: Re: [PATCH 2/2] dmaengine: omap-dma: Support for slave devices with
 data port window

On Tue, Oct 25, 2016 at 01:50:19PM +0300, Peter Ujfalusi wrote:
> Based on the src/dst_port_window_size - if it is set - configure the DMA
> channel to use double indexing in order to be able to loop within the
> address window.
> 
> Signed-off-by: Peter Ujfalusi <peter.ujfalusi@...com>
> ---
>  drivers/dma/omap-dma.c | 45 +++++++++++++++++++++++++++++++++++++++++++--
>  1 file changed, 43 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c
> index 025f499cb20d..29350f936154 100644
> --- a/drivers/dma/omap-dma.c
> +++ b/drivers/dma/omap-dma.c
> @@ -166,6 +166,9 @@ enum {
>  	CSDP_DST_BURST_16	= 1 << 14,
>  	CSDP_DST_BURST_32	= 2 << 14,
>  	CSDP_DST_BURST_64	= 3 << 14,
> +	CSDP_WRITE_NON_POSTED	= (0 << 16),
> +	CSDP_WRITE_POSTED	= (1 << 16),
> +	CSDP_WRITE_LAST_NON_POSTED = (2 << 16),

Why the useless parens?

> +		if (port_window) {
> +			d->ccr |= CCR_SRC_AMODE_DBLIDX;
> +			d->ei = 1;
> +			d->fi = (-1) * (port_window - 1);

You know that's 1 - port_window, or -(port_window - 1).

> +
> +			if (port_window / 64)
> +				d->csdp = CSDP_SRC_BURST_64 | CSDP_SRC_PACKED;
> +			else if (port_window / 32)
> +				d->csdp = CSDP_SRC_BURST_32 | CSDP_SRC_PACKED;
> +			else if (port_window / 16)
> +				d->csdp = CSDP_SRC_BURST_16 | CSDP_SRC_PACKED;

Why these divisions?  Wouldn't >= be more suitable here?  Do they even
make sense here?

> +		} else {
> +			d->ccr |= CCR_SRC_AMODE_CONSTANT;
> +		}
>  	} else {
> -		d->ccr |= CCR_DST_AMODE_CONSTANT | CCR_SRC_AMODE_POSTINC;
>  		d->csdp = CSDP_SRC_BURST_64 | CSDP_SRC_PACKED;
> +
> +		d->ccr |= CCR_SRC_AMODE_POSTINC;
> +		if (port_window) {
> +			d->ccr |= CCR_DST_AMODE_DBLIDX;
> +
> +			if (port_window / 64)
> +				d->csdp = CSDP_DST_BURST_64 | CSDP_DST_PACKED;
> +			else if (port_window / 32)
> +				d->csdp = CSDP_DST_BURST_32 | CSDP_DST_PACKED;
> +			else if (port_window / 16)
> +				d->csdp = CSDP_DST_BURST_16 | CSDP_DST_PACKED;

Ditto.

> +		} else {
> +			d->ccr |= CCR_DST_AMODE_CONSTANT;
> +		}
>  	}
>  
>  	d->cicr = CICR_DROP_IE | CICR_BLOCK_IE;
> @@ -945,6 +979,9 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
>  			d->ccr |= CCR_TRIGGER_SRC;
>  
>  		d->cicr |= CICR_MISALIGNED_ERR_IE | CICR_TRANS_ERR_IE;
> +
> +		if (port_window)
> +			d->csdp |= CSDP_WRITE_LAST_NON_POSTED;
>  	}
>  	if (od->plat->errata & DMA_ERRATA_PARALLEL_CHANNELS)
>  		d->clnk_ctrl = c->dma_ch;
> @@ -970,6 +1007,10 @@ static struct dma_async_tx_descriptor *omap_dma_prep_slave_sg(
>  		osg->addr = sg_dma_address(sgent);
>  		osg->en = en;
>  		osg->fn = sg_dma_len(sgent) / frame_bytes;
> +		if (port_window && dir == DMA_MEM_TO_DEV) {
> +			osg->ei = 1;
> +			osg->fi = (-1) * (port_window - 1);

Same as above.

-- 
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