linux-kernel - Re: [PATCH 1/2] dmaengine: sun6i: make gate bit in sun8i's DMA engines a common quirk

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Message-ID: <20170614083252.GK13020@localhost>
Date:   Wed, 14 Jun 2017 14:02:52 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        Chen-Yu Tsai <wens@...e.org>, dmaengine@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-sunxi@...glegroups.com, Icenowy Zheng <icenowy@...c.xyz>
Subject: Re: [PATCH 1/2] dmaengine: sun6i: make gate bit in sun8i's DMA
 engines a common quirk

On Mon, Jun 05, 2017 at 08:33:47PM +0800, Icenowy Zheng wrote:
> From: Icenowy Zheng <icenowy@...c.xyz>
> 
> Originally we enable a special gate bit when the compatible indicates
> A23/33.
> 
> But according to BSP sources and user manuals, more SoCs will need this
> gate bit.
> 
> So make it a common quirk configured in the config struct.
> 
> Signed-off-by: Icenowy Zheng <icenowy@...c.xyz>
> ---
> Changes since original codec patchset v3:
> - Refactored comments to cover some words found in official documents.
> - Removed the comments when toggling the gate bit.
> 
>  drivers/dma/sun6i-dma.c | 20 +++++++++++++-------
>  1 file changed, 13 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> index a2358780ab2c..252b59c1d1d5 100644
> --- a/drivers/dma/sun6i-dma.c
> +++ b/drivers/dma/sun6i-dma.c
> @@ -101,6 +101,17 @@ struct sun6i_dma_config {
>  	u32 nr_max_channels;
>  	u32 nr_max_requests;
>  	u32 nr_max_vchans;
> +	/*
> +	 * In the datasheets/user manuals of newer Allwinner SoCs, a special
> +	 * bit (bit 2 at register 0x20) is present.
> +	 * It's named "DMA MCLK interface circuit auto gating bit" in the
> +	 * documents, and the footnote of this register says that this bit
> +	 * should be set up when initializing the DMA controller.
> +	 * Allwinner A23/A33 user manuals do not have this bit documented,
> +	 * however these SoCs really have and need this bit, as seen in the
> +	 * BSP kernel source code.
> +	 */
> +	bool gate_needed;

Since this is a hw property, why is this not added as an optional DT
property?

>  };
>  
>  /*
> @@ -1009,6 +1020,7 @@ static struct sun6i_dma_config sun8i_a23_dma_cfg = {
>  	.nr_max_channels = 8,
>  	.nr_max_requests = 24,
>  	.nr_max_vchans   = 37,
> +	.gate_needed	 = true,
>  };
>  
>  static struct sun6i_dma_config sun8i_a83t_dma_cfg = {
> @@ -1174,13 +1186,7 @@ static int sun6i_dma_probe(struct platform_device *pdev)
>  		goto err_dma_unregister;
>  	}
>  
> -	/*
> -	 * sun8i variant requires us to toggle a dma gating register,
> -	 * as seen in Allwinner's SDK. This register is not documented
> -	 * in the A23 user manual.
> -	 */
> -	if (of_device_is_compatible(pdev->dev.of_node,
> -				    "allwinner,sun8i-a23-dma"))
> +	if (sdc->cfg->gate_needed)
>  		writel(SUN8I_DMA_GATE_ENABLE, sdc->base + SUN8I_DMA_GATE);
>  
>  	return 0;
> -- 
> 2.12.2
> 

-- 
~Vinod