linux-kernel - Re: [PATCH 3/3] dmaengine: sun6i: Add support for Allwinner A64

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Message-ID: <20170901060445.vboici7qxfkztp3s@flea>
Date:   Fri, 1 Sep 2017 08:04:45 +0200
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Andre Przywara <andre.przywara@....com>
Cc:     Stefan Brüns <stefan.bruens@...h-aachen.de>,
        linux-sunxi@...glegroups.com, Chen-Yu Tsai <wens@...e.org>,
        devicetree@...r.kernel.org, dmaengine@...r.kernel.org,
        Vinod Koul <vinod.koul@...el.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] dmaengine: sun6i: Add support for Allwinner A64

On Fri, Sep 01, 2017 at 01:31:35AM +0100, Andre Przywara wrote:
> Hi,
> 
> On 31/08/17 00:36, Stefan Brüns wrote:
> > The A64 SoC has the same dma engine as the H3 (sun8i), with a
> > reduced amount of physical channels. Add the proper config data
> > and compatible string to support it.
> 
> ...
> 
> > diff --git a/drivers/dma/sun6i-dma.c b/drivers/dma/sun6i-dma.c
> > index 5f4eee4513e5..6a17c5d63582 100644
> > --- a/drivers/dma/sun6i-dma.c
> > +++ b/drivers/dma/sun6i-dma.c
> > @@ -1068,6 +1068,12 @@ static struct sun6i_dma_config sun8i_h3_dma_cfg = {
> >  	.nr_max_vchans   = 34,
> >  	.dmac_variant    = DMAC_VARIANT_H3,
> >  };
> > +
> > +static struct sun6i_dma_config sun50i_a64_dma_cfg = {
> > +	.nr_max_channels = 8,
> > +	.nr_max_requests = 27,
> > +	.nr_max_vchans   = 38,
> > +	.dmac_variant    = DMAC_VARIANT_H3,
> >  };
> >  
> >  static const struct of_device_id sun6i_dma_match[] = {
> > @@ -1075,6 +1081,7 @@ static const struct of_device_id sun6i_dma_match[] = {
> >  	{ .compatible = "allwinner,sun8i-a23-dma", .data = &sun8i_a23_dma_cfg },
> >  	{ .compatible = "allwinner,sun8i-a83t-dma", .data = &sun8i_a83t_dma_cfg },
> >  	{ .compatible = "allwinner,sun8i-h3-dma", .data = &sun8i_h3_dma_cfg },
> > +	{ .compatible = "allwinner,sun50i-a64-dma", .data = &sun50i_a64_dma_cfg },
> >  	{ /* sentinel */ }
> >  };
> >  MODULE_DEVICE_TABLE(of, sun6i_dma_match);
> 
> I was wondering if should use the opportunity to expose those values as
> DT properties instead of hard-wiring them to a compatible string in the
> driver every time we add support for a new SoC?
> We could introduce a new compatible string (say: "allwinner,sunxi-dma"),
> then describe properties for the number of channels and requests and
> vchans and parse those from the DT at probe time.
> With this we might be able to support future SoCs without Linux *driver*
> changes, by just providing the right DT. This would have worked already
> for instance for the A83T support, which just changed those values.
> 
> For instance with this quick patch below (just compile tested, and without
> your refactoring).
> The DT node would then read something like:
> 	dma: dma-controller@...02000 {
> 		compatible = "allwinner,sun50i-a64-dma",
> 			     "allwinner,sunxi-dma";
> 		reg = <0x01c02000 0x1000>;
> 		interrupts = <GIC_SPI 50 IRQ_TYPE_LEVEL_HIGH>;
> 		clocks = <&ccu CLK_BUS_DMA>;
> 		resets = <&ccu RST_BUS_DMA>;
> 		#dma-cells = <1>;
> 		allwinner,max_channels = <8>;
> 		allwinner,max_requests = <27>;
> 		allwinner,max_vchans = <38>;
> 	};

We're still going to need a different compatible anyway, so it's not
really like it would change anything.

Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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