linux-kernel - Re: [PATCH v2 2/3] dma: imx-sdma: add clock ratio 1:1 check

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Date:   Mon, 21 Jan 2019 10:17:42 +0100
From:   Lucas Stach <l.stach@...gutronix.de>
To:     "Angus Ainslie (Purism)" <angus@...ea.ca>
Cc:     linux-kernel@...r.kernel.org, Vinod Koul <vkoul@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        dmaengine@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 2/3] dma: imx-sdma: add clock ratio 1:1 check

Hi Angus,

Am Samstag, den 19.01.2019, 19:31 -0700 schrieb Angus Ainslie (Purism):
> On i.mx8 mscale B0 chip, AHB/SDMA clock ratio 2:1 can't be supportted,
> since SDMA clock ratio has to be increased to 250Mhz, AHB can't reach
> to 500Mhz, so use 1:1 instead.
> 
> based on NXP commit MLK-16841-1
> 
> > Signed-off-by: Angus Ainslie (Purism) <angus@...ea.ca>
> ---
>  .../devicetree/bindings/dma/fsl-imx-sdma.txt  |  1 +
>  drivers/dma/imx-sdma.c                        | 20 +++++++++++++++----
>  2 files changed, 17 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> index 3c9a57a8443b..17544c1820b7 100644
> --- a/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> +++ b/Documentation/devicetree/bindings/dma/fsl-imx-sdma.txt
> @@ -67,6 +67,7 @@ Optional properties:
>      reg is the GPR register offset.
>      shift is the bit position inside the GPR register.
>      val is the value of the bit (0 or 1).
> +- fsl,ratio-1-1: AHB/SDMA core clock ration 1:1, 2:1 without this.

Why does this need a separate DT property? Shouldn't the driver be able
to infer this from the clock rates going into the SDMA hardware?

Regards,
Lucas

>  Examples:
>  
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index 0b3a67ff8e82..65dada21d3c1 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -440,6 +440,8 @@ struct sdma_engine {
> > >  	unsigned int			irq;
> > >  	dma_addr_t			bd0_phys;
> > >  	struct sdma_buffer_descriptor	*bd0;
> > +	/* clock ratio for AHB:SDMA core. 1:1 is 1, 2:1 is 0*/
> > > +	bool				clk_ratio;
>  };
>  
>  static int sdma_config_write(struct dma_chan *chan,
> @@ -662,8 +664,14 @@ static int sdma_run_channel0(struct sdma_engine *sdma)
> >  		dev_err(sdma->dev, "Timeout waiting for CH0 ready\n");
>  
> >  	/* Set bits of CONFIG register with dynamic context switching */
> > -	if (readl(sdma->regs + SDMA_H_CONFIG) == 0)
> > -		writel_relaxed(SDMA_H_CONFIG_CSM, sdma->regs + SDMA_H_CONFIG);
> > +	if (readl(sdma->regs + SDMA_H_CONFIG) == 0) {
> > +		if (sdma->clk_ratio)
> > +			reg = SDMA_H_CONFIG_CSM | SDMA_H_CONFIG_ACR;
> > +		else
> > +			reg = SDMA_H_CONFIG_CSM;
> +
> > +		writel_relaxed(reg, sdma->regs + SDMA_H_CONFIG);
> > +	}
>  
> >  	return ret;
>  }
> @@ -1880,8 +1888,10 @@ static int sdma_init(struct sdma_engine *sdma)
> >  	writel_relaxed(0x4050, sdma->regs + SDMA_CHN0ADDR);
>  
> >  	/* Set bits of CONFIG register but with static context switching */
> > -	/* FIXME: Check whether to set ACR bit depending on clock ratios */
> > -	writel_relaxed(0, sdma->regs + SDMA_H_CONFIG);
> > +	if (sdma->clk_ratio)
> > +		writel_relaxed(SDMA_H_CONFIG_ACR, sdma->regs + SDMA_H_CONFIG);
> > +	else
> > +		writel_relaxed(0, sdma->regs + SDMA_H_CONFIG);
>  
> >  	writel_relaxed(ccb_phys, sdma->regs + SDMA_H_C0PTR);
>  
> @@ -1975,6 +1985,8 @@ static int sdma_probe(struct platform_device *pdev)
> >  	if (!sdma)
> >  		return -ENOMEM;
>  
> > +	sdma->clk_ratio = of_property_read_bool(np, "fsl,ratio-1-1");
> +
> >  	spin_lock_init(&sdma->channel_0_lock);
>  
> >  	sdma->dev = &pdev->dev;