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: <20170614084529.GL13020@localhost>
Date:   Wed, 14 Jun 2017 14:15:29 +0530
From:   Vinod Koul <vinod.koul@...el.com>
To:     Icenowy Zheng <icenowy@...c.io>
Cc:     linux-arm-kernel@...ts.infradead.org, Chen-Yu Tsai <wens@...e.org>,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
        Icenowy Zheng <icenowy@...c.xyz>, dmaengine@...r.kernel.org,
        Maxime Ripard <maxime.ripard@...e-electrons.com>
Subject: Re: [PATCH 1/2] dmaengine: sun6i: make gate bit in sun8i's DMA
 engines a common quirk

On Wed, Jun 14, 2017 at 04:32:57PM +0800, Icenowy Zheng wrote:
> 
> 
> 于 2017年6月14日 GMT+08:00 下午4:32:52, Vinod Koul <vinod.koul@...el.com> 写到:
> >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?
> 
> As it's SoC-specified.
> 
> Some SoCs need it, and some don't.

and that is the reason it should be a property

> 
> SoC info is in compatible, so there's no reason to make it a property.

that's why it would need to be optional for the SoC's that needs these..

> 
> >
> >>  };
> >>  
> >>  /*
> >> @@ -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