linux-kernel - Re: [PATCH v2 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire Interface) controller support

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Date:	Fri, 09 May 2014 17:01:04 +0200
From:	Hans de Goede <hdegoede@...hat.com>
To:	Boris BREZILLON <boris.brezillon@...e-electrons.com>,
	Maxime Ripard <maxime.ripard@...e-electrons.com>
CC:	Wolfram Sang <wsa@...-dreams.de>,
	Randy Dunlap <rdunlap@...radead.org>,
	Shuge <shuge@...winnertech.com>, kevin@...winnertech.com,
	devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire Interface)
 controller support

Hi,

On 05/09/2014 04:50 PM, Boris BREZILLON wrote:
> 
> On 09/05/2014 16:31, Maxime Ripard wrote:
>> Hi Boris,
>>
>> On Wed, May 07, 2014 at 07:58:35PM +0200, Boris BREZILLON wrote:
>>
> [...]
>> +
>> +	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> +	p2wi->regs = devm_ioremap_resource(dev, r);
>> +	if (IS_ERR(p2wi->regs)) {
>> +		dev_err(dev, "failed to retrieve iomem resource\n");
>> +		return PTR_ERR(p2wi->regs);
>> You seem to be returning the error code in the next error messages. It
>> would probably be a good idea to put it there too.
> 
> Yes, I'll print the err code in the error message.
> 
>>
>>> +	}
>>> +
>>> +	snprintf(p2wi->adapter.name, sizeof(p2wi->adapter.name), pdev->name);
>>> +	ret = platform_get_irq(pdev, 0);
>>> +	if (ret < 0) {
>>> +		dev_err(dev, "failed to retrieve irq: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +	p2wi->irq = ret;
>>> +
>>> +	p2wi->clk = devm_clk_get(dev, NULL);
>>> +	if (IS_ERR(p2wi->clk)) {
>>> +		ret = PTR_ERR(p2wi->clk);
>>> +		dev_err(dev, "failed to retrieve clk: %d\n",
>>> +			ret);
>>> +		return ret;
>>> +	}
>>> +
>>> +	ret = clk_prepare_enable(p2wi->clk);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed to enable clk: %d\n", ret);
>>> +		return ret;
>>> +	}
>>> +
>>> +	parent_clk_freq = clk_get_rate(p2wi->clk);
>>> +
>>> +	p2wi->rstc = devm_reset_control_get(dev, NULL);
>>> +	if (IS_ERR(p2wi->rstc)) {
>>> +		ret = PTR_ERR(p2wi->rstc);
>>> +		dev_err(dev, "failed to retrieve reset controller: %d\n",
>>> +			ret);
>>> +		goto err_clk_disable;
>>> +	}
>>> +
>>> +	ret = reset_control_deassert(p2wi->rstc);
>>> +	if (ret) {
>>> +		dev_err(dev, "failed to deassert reset line: %d\n",
>>> +			ret);
>>> +		goto err_clk_disable;
>>> +	}
>>> +
>>> +	init_completion(&p2wi->complete);
>>> +	p2wi->adapter.dev.parent = dev;
>>> +	p2wi->adapter.algo = &p2wi_algo;
>>> +	p2wi->adapter.owner = THIS_MODULE;
>>> +	p2wi->adapter.dev.of_node = pdev->dev.of_node;
>>> +	platform_set_drvdata(pdev, p2wi);
>>> +	i2c_set_adapdata(&p2wi->adapter, p2wi);
>>> +
>>> +	ret = devm_request_irq(dev, p2wi->irq, p2wi_interrupt, 0, pdev->name,
>>> +			       p2wi);
>>> +	if (ret) {
>>> +		dev_err(dev, "can't register interrupt handler irq%d: %d\n",
>>> +			p2wi->irq, ret);
>>> +		goto err_reset_assert;
>>> +	}
>>> +
>>> +	writel(P2WI_CTRL_SOFT_RST, p2wi->regs + P2WI_CTRL);
>>> +
>>> +	clk_div = parent_clk_freq / clk_freq;
>>> +	if (!clk_div) {
>>> +		dev_warn(dev,
>>> +			 "clock-frequency is too high, setting it to %lu Hz\n",
>>> +			 parent_clk_freq);
>>> +		clk_div = 1;
>>> +	} else if (clk_div > P2WI_CCR_MAX_CLK_DIV) {
>>> +		dev_warn(dev,
>>> +			 "clock-frequency is too low, setting it to %lu Hz\n",
>>> +			 parent_clk_freq / P2WI_CCR_MAX_CLK_DIV);
>>> +		clk_div = P2WI_CCR_MAX_CLK_DIV;
>>> +	}
>>> +
>>> +	writel(P2WI_CCR_SDA_OUT_DELAY(1) | P2WI_CCR_CLK_DIV(clk_div),
>>> +	       p2wi->regs + P2WI_CCR);
>>> +
>>> +	if (p2wi_mode_reg >= 0 && p2wi_mode_val >= 0) {
>>> +		writel(P2WI_PMCR_PMU_INIT_SEND |
>>> +		       P2WI_PMCR_PMU_MODE_REG(p2wi_mode_reg) |
>>> +		       P2WI_PMCR_PMU_INIT_DATA(p2wi_mode_val) |
>>> +		       P2WI_PMCR_PMU_DEV_ADDR(p2wi->slave_addr),
>>> +		       p2wi->regs + P2WI_PMCR);
>>> +
>>> +		while (readl(p2wi->regs + P2WI_PMCR) &
>>> +		       P2WI_PMCR_PMU_INIT_SEND)
>>> +			cpu_relax();
>>> +	}
>> Did we actually encounter such a case? From what I've seen so far,
>> both community's u-boot and Allwinner's bootloader already do this.
>>
>> As you know, I'm really not fond of putting random values and
>> registers offsets into the DT itself. Making the assumption that the
>> PMIC is already switched to P2WI by the bootloader seems pretty safe
>> to me.
> 
> Hans, any opinion ?

I think that Maxime is right, any bootloader will need to kick the
pmic to set dram voltage, etc. So it is pretty safe to assume this is
already done and just remove the code.

Regards,

Hans
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