Re: [RESEND2 PATCH v4 2/2] i2c: sunxi: add P2WI (Push/Pull 2 Wire Interface) controller support

[Boris BREZILLON <boris.brezillon@free-electrons.com>]

On 10/06/2014 10:54, Boris BREZILLON wrote:
> Hello Wolfram,
>
> On 10/06/2014 10:38, Wolfram Sang wrote:
>> On Tue, Jun 03, 2014 at 10:49:52AM +0200, Boris BREZILLON wrote:
>>> The P2WI looks like an SMBus controller which only supports byte data
>>> transfers. But, it differs from standard SMBus protocol on several
>>> aspects:
>>> - it supports only one slave device, and thus drop the address field
>>> - it adds a parity bit every 8bits of data
>>> - only one read access is required to read a byte (instead of a read
>>>   followed by a write access in standard SMBus protocol)
>>> - there's no Ack bit after each byte transfer
>>>
>>> This means this bus cannot be used to interface with standard SMBus
>>> devices (the only known device to support this interface is the AXP221
>>> PMIC).
>> Good description. Should be a comment at the top of the driver to spread
>> the word.
> Sure, I'll copy this description in the driver.
>
>>> Signed-off-by: Boris BREZILLON <boris.brezillon@free-electrons.com>
>>> Acked-by: Maxime Ripard <maxime.ripard@free-electrons.com>
>>> ---
>>>  drivers/i2c/busses/Kconfig          |  12 ++
>>>  drivers/i2c/busses/Makefile         |   1 +
>>>  drivers/i2c/busses/i2c-sun6i-p2wi.c | 349 ++++++++++++++++++++++++++++++++++++
>>>  3 files changed, 362 insertions(+)
>>>  create mode 100644 drivers/i2c/busses/i2c-sun6i-p2wi.c
>> ...
>>
>>> +struct p2wi {
>>> +	struct i2c_adapter adapter;
>>> +	struct completion complete;
>>> +	unsigned int irq;
>> Can be a local variable in probe.
> Yes, I'll remove it from this structure.
>
>>> +	unsigned int status;
>>> +	void __iomem *regs;
>>> +	struct clk *clk;
>>> +	struct reset_control *rstc;
>>> +	int slave_addr;
>>> +};
>>> +
>>> +static irqreturn_t p2wi_interrupt(int irq, void *dev_id)
>>> +{
>>> +	struct p2wi *p2wi = dev_id;
>>> +	unsigned long status;
>>> +
>>> +	status = readl(p2wi->regs + P2WI_INTS);
>>> +	p2wi->status = status;
>>> +
>>> +	/* Clear interrupts */
>>> +	status &= (P2WI_INTS_LOAD_BSY | P2WI_INTS_TRANS_ERR |
>>> +		   P2WI_INTS_TRANS_OVER);
>>> +	writel(status, p2wi->regs + P2WI_INTS);
>>> +
>>> +	complete(&p2wi->complete);
>>> +
>>> +	return IRQ_HANDLED;
>>> +}
>>> +
>>> +static u32 p2wi_functionality(struct i2c_adapter *adap)
>>> +{
>>> +	return I2C_FUNC_SMBUS_BYTE_DATA;
>>> +}
>>> +
>>> +static int p2wi_smbus_xfer(struct i2c_adapter *adap, u16 addr,
>>> +			   unsigned short flags, char read_write,
>>> +			   u8 command, int size, union i2c_smbus_data *data)
>>> +{
>>> +	struct p2wi *p2wi = i2c_get_adapdata(adap);
>>> +	unsigned long dlen = P2WI_DLEN_DATA_LENGTH(1);
>>> +
>>> +	if (addr > 0xff ||
>> Why 0xff? Does the PMIC support that? I2C addresses are 7-bit. You
>> won't even have a slave device if it has an illegal i2c address, so this
>> shouldn't happen.
> The P2WI protocol supports 8bits addresses, hence I added this 0xff check.
> Anyway, the PMIC I use (AXP221) is assigned the 0x68 address, and I
> don't think there are a lot of P2WI compatible devices in the wild, so
> we can just assume 7bits addresses are fine and rely on the core code
> checks.

My bad, the P2WI protocol does not have any address concept.
The 0xff value come from the P2WI_PMCR_PMU_DEV_ADDR field which is
specified to be 8 bits large.
Anyway, this does not change the fact that we can remove this check.

>
>>> +	    (p2wi->slave_addr >= 0 && addr != p2wi->slave_addr)) {
>>> +		dev_err(&adap->dev, "invalid P2WI address\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	if (!data)
>>> +		return -EINVAL;
>>> +
>>> +	writel(command, p2wi->regs + P2WI_DADDR0);
>>> +
>>> +	if (read_write == I2C_SMBUS_READ)
>>> +		dlen |= P2WI_DLEN_READ;
>>> +	else
>>> +		writel(data->byte, p2wi->regs + P2WI_DATA0);
>>> +
>>> +	writel(dlen, p2wi->regs + P2WI_DLEN);
>>> +
>>> +	if (readl(p2wi->regs + P2WI_CTRL) & P2WI_CTRL_START_TRANS) {
>>> +		dev_err(&adap->dev, "P2WI bus busy\n");
>>> +		return -EBUSY;
>>> +	}
>>> +
>>> +	reinit_completion(&p2wi->complete);
>>> +
>>> +	writel(P2WI_INTS_LOAD_BSY | P2WI_INTS_TRANS_ERR | P2WI_INTS_TRANS_OVER,
>>> +	       p2wi->regs + P2WI_INTE);
>>> +
>>> +	writel(P2WI_CTRL_START_TRANS | P2WI_CTRL_GLOBAL_INT_ENB,
>>> +	       p2wi->regs + P2WI_CTRL);
>>> +
>>> +	wait_for_completion(&p2wi->complete);
>>> +
>>> +	if (p2wi->status & P2WI_INTS_LOAD_BSY) {
>>> +		dev_err(&adap->dev, "P2WI bus busy\n");
>>> +		return -EBUSY;
>>> +	}
>>> +
>>> +	if (p2wi->status & P2WI_INTS_TRANS_ERR) {
>>> +		dev_err(&adap->dev, "P2WI bus xfer error\n");
>>> +		return -ENXIO;
>>> +	}
>>> +
>>> +	if (read_write == I2C_SMBUS_READ)
>>> +		data->byte = readl(p2wi->regs + P2WI_DATA0);
>>> +
>>> +	return 0;
>>> +}
>>> +
>>> +static const struct i2c_algorithm p2wi_algo = {
>>> +	.smbus_xfer = p2wi_smbus_xfer,
>>> +	.functionality = p2wi_functionality,
>>> +};
>>> +
>>> +static const struct of_device_id p2wi_of_match_table[] = {
>>> +	{ .compatible = "allwinner,sun6i-a31-p2wi" },
>>> +	{}
>>> +};
>>> +MODULE_DEVICE_TABLE(of, p2wi_of_match_table);
>>> +
>>> +static int p2wi_probe(struct platform_device *pdev)
>>> +{
>>> +	struct device *dev = &pdev->dev;
>>> +	struct device_node *np = dev->of_node;
>>> +	struct device_node *childnp;
>>> +	unsigned long parent_clk_freq;
>>> +	u32 clk_freq = 100000;
>>> +	struct resource *r;
>>> +	struct p2wi *p2wi;
>>> +	u32 slave_addr;
>>> +	int clk_div;
>>> +	int ret;
>>> +
>>> +	of_property_read_u32(np, "clock-frequency", &clk_freq);
>>> +	if (clk_freq > P2WI_MAX_FREQ) {
>>> +		dev_err(dev,
>>> +			"required clock-frequency (%u Hz) is too high (max = 6MHz)",
>>> +			clk_freq);
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	if (of_get_child_count(np) > 1) {
>>> +		dev_err(dev, "P2WI only supports one slave device\n");
>>> +		return -EINVAL;
>>> +	}
>>> +
>>> +	p2wi = devm_kzalloc(dev, sizeof(struct p2wi), GFP_KERNEL);
>>> +	if (!p2wi) {
>>> +		dev_err(dev, "failed to allocate p2wi struct\n");
>> No error strings for OOM.
> I'll drop this line.
>
>>> +		return -ENOMEM;
>>> +	}
>>> +
>>> +	p2wi->slave_addr = -1;
>>> +
>>> +	/*
>>> +	 * Authorize a p2wi node without any children to be able to use an
>>> +	 * i2c-dev from userpace.
>>> +	 * In this case the slave_addr is set to -1 and won't be checked when
>>> +	 * launching a P2WI transfer.
>>> +	 */
>>> +	childnp = of_get_next_available_child(np, NULL);
>>> +	if (childnp) {
>>> +		ret = of_property_read_u32(childnp, "reg", &slave_addr);
>>> +		if (ret || slave_addr > 0xff) {
>> Again: Is 8 bit range important here? Otherwise I'd leave the check to the
>> core.
>>
>>> +			dev_err(dev, "invalid slave address on node %s\n",
>>> +				childnp->full_name);
>>> +			return -EINVAL;
>>> +		}
>>> +
>>> +		p2wi->slave_addr = slave_addr;
>>> +	}
>>> +
>>> +	r = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>>> +	p2wi->regs = devm_ioremap_resource(dev, r);
>>> +	if (IS_ERR(p2wi->regs)) {
>>> +		ret = PTR_ERR(p2wi->regs);
>>> +		dev_err(dev, "failed to retrieve iomem resource: %d\n", ret);
>> devm_ioremap_resource prints errors on its own.
> Ditto
>
>>> +		return ret;
>>> +	}
>>> +
>>> +	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);
>> My general suggestion: Don't be too strict on the 80 char limit. IMO this dangling
>> 'ret' is not more readable.
> Okay, I'll fix that.
>
>
> Thanks for your review.
>
> Best Regards,
>
> Boris
>

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