linux-kernel - Re: [PATCH 07/10] dmaengine: sun6i: Retrieve channel count/max request from devicetree

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Date:   Mon, 4 Sep 2017 00:44:54 +0100
From:   André Przywara <andre.przywara@....com>
To:     Stefan Brüns <stefan.bruens@...h-aachen.de>,
        linux-sunxi@...glegroups.com
Cc:     devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
        Vinod Koul <vinod.koul@...el.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, Rob Herring <robh+dt@...nel.org>,
        Code Kipper <codekipper@...il.com>
Subject: Re: [PATCH 07/10] dmaengine: sun6i: Retrieve channel count/max
 request from devicetree

Hi,

On 03/09/17 23:40, Stefan Brüns wrote:
> To avoid introduction of a new compatible for each small SoC/DMA controller
> variation, move the definition of the channel count to the devicetree.
> 
> The number of vchans is no longer explicit, but limited by the highest
> port/DMA request number. The result is a slight overallocation for SoCs
> with a sparse port mapping.
> 
> Signed-off-by: Stefan Brüns <stefan.bruens@...h-aachen.de>
> ---
>  drivers/dma/sun6i-dma.c | 35 ++++++++++++++++++++++++++++++++++-
>  1 file changed, 34 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index c69dadb853d2..bd4c2e4a759b 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -42,6 +42,9 @@
>  
>  #define DMA_STAT		0x30
>  
> +/* Offset between DMA_IRQ_EN and DMA_IRQ_STAT limits number of channels */
> +#define DMA_MAX_CHANNELS	(DMA_IRQ_CHAN_NR * 0x10 / 4)
> +
>  /*
>   * sun8i specific registers
>   */
> @@ -65,7 +68,8 @@
>  #define DMA_CHAN_LLI_ADDR	0x08
>  
>  #define DMA_CHAN_CUR_CFG	0x0c
> -#define DMA_CHAN_CFG_SRC_DRQ(x)		((x) & 0x1f)
> +#define DMA_CHAN_MAX_DRQ		0x1f
> +#define DMA_CHAN_CFG_SRC_DRQ(x)		((x) & DMA_CHAN_MAX_DRQ)
>  #define DMA_CHAN_CFG_SRC_IO_MODE	BIT(5)
>  #define DMA_CHAN_CFG_SRC_LINEAR_MODE	(0 << 5)
>  #define DMA_CHAN_CFG_SRC_BURST_A31(x)	(((x) & 0x3) << 7)
> @@ -1173,6 +1177,35 @@ static int sun6i_dma_probe(struct platform_device *pdev)
>  	sdc->num_vchans = sdc->cfg->nr_max_vchans;
>  	sdc->max_request = sdc->cfg->nr_max_requests;
>  
> +	ret = of_property_read_u32(np, "dma-channels", &sdc->num_pchans);
> +	if (ret && !sdc->num_pchans) {
> +		dev_err(&pdev->dev, "Can't get dma-channels.\n");
> +		return ret;
> +	}
> +
> +	if (sdc->num_pchans > DMA_MAX_CHANNELS) {
> +		dev_err(&pdev->dev, "Number of dma-channels out of range.\n");
> +		return -EINVAL;
> +	}
> +
> +	ret = of_property_read_u32(np, "dma-requests", &sdc->max_request);
> +	if (ret && !sdc->max_request) {
> +		dev_info(&pdev->dev, "Missing dma-requests, using %u.\n",
> +			 DMA_CHAN_MAX_DRQ);

Mmmh, is this mapping of "!sdc->max_request" -> DMA_CHAN_MAX_DRQ
implemented somewhere else? Or is it just missing here:
		sdc->max_request = DMA_CHAN_MAX_DRQ;

Otherwise this is looking good, thanks for picking up the DT property
approach!

Cheers,
Andre.

> +	}
> +
> +	if (sdc->max_request > DMA_CHAN_MAX_DRQ) {
> +		dev_err(&pdev->dev, "Value of dma-requests out of range.\n");
> +		return -EINVAL;
> +	}
> +
> +	/*
> +	 * If the number of vchans is not specified, derive it from the
> +	 * highest port number, at most one channel per port and direction.
> +	 */
> +	if (!sdc->num_vchans)
> +		sdc->num_vchans = 2 * (sdc->max_request + 1);
> +
>  	sdc->pchans = devm_kcalloc(&pdev->dev, sdc->num_pchans,
>  				   sizeof(struct sun6i_pchan), GFP_KERNEL);
>  	if (!sdc->pchans)
>