Re: [PATCH] i2c: axxia: Add I2C driver for AXM55xx

[Wolfram Sang]

Hi,

thanks for the submission.

On Mon, Aug 25, 2014 at 01:51:22PM +0200, Anders Berg wrote:
> Add I2C bus driver for the controller found in the LSI Axxia family SoCs. The
> driver implements 10-bit addressing and SMBus transfer modes via emulation
> (including SMBus block data read).
> 
> Signed-off-by: Anders Berg <anders.berg@xxxxxxxxxxxxx>

Looks pretty good already. Still, some comments:

> +config I2C_AXXIA
> +	tristate "Axxia I2C controller"
> +	depends on ARCH_AXXIA
> +	help
> +	  Say yes if you want to support the I2C bus on Axxia platforms.
> +
> +	  If you don't know, say Y.

I'd say skip this sentence and consider 'default y' if it is really
needed on this platform.

> diff --git a/drivers/i2c/busses/i2c-axxia.c b/drivers/i2c/busses/i2c-axxia.c
> new file mode 100644
> index 0000000..e6c9b88
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-axxia.c
> @@ -0,0 +1,591 @@
> +/*
> + * drivers/i2c/busses/i2c-axxia.c

No pathnames please, they might get stale.

> + *
> + * This driver implements I2C master functionality using the LSI API2C
> + * controller.
> + *
> + * This software is licensed under the terms of the GNU General Public
> + * License version 2, as published by the Free Software Foundation, and
> + * may be copied, distributed, and modified under those terms.
> + */
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/init.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/platform_device.h>

At least of.h, too?

> +
> +#define SCL_WAIT_TIMEOUT_NS 25000000
> +#define I2C_XFER_TIMEOUT    (msecs_to_jiffies(250))
> +#define I2C_STOP_TIMEOUT    (msecs_to_jiffies(100))
> +#define FIFO_SIZE           8
> +
> +#define GLOBAL_CONTROL		0x00
> +#define   GLOBAL_MST_EN         BIT(0)
> +#define   GLOBAL_SLV_EN         BIT(1)
> +#define   GLOBAL_IBML_EN        BIT(2)
> +#define INTERRUPT_STATUS	0x04
> +#define INTERRUPT_ENABLE	0x08
> +#define   INT_SLV               BIT(1)
> +#define   INT_MST               BIT(0)
> +#define WAIT_TIMER_CONTROL	0x0c
> +#define   WT_EN			BIT(15)
> +#define   WT_VALUE(_x)		((_x) & 0x7fff)
> +#define IBML_TIMEOUT		0x10
> +#define IBML_LOW_MEXT		0x14
> +#define IBML_LOW_SEXT		0x18
> +#define TIMER_CLOCK_DIV		0x1c
> +#define I2C_BUS_MONITOR		0x20
> +#define SOFT_RESET		0x24
> +#define MST_COMMAND		0x28
> +#define   CMD_BUSY		(1<<3)

The whole driver has 'spaces around operator' issues, please fix them.

...


> +	/* Find the prescaler value that makes tmo_clk fit in 15-bits counter.
> +	 */

Minor: Make this a one line comment. Better readable.

...


> +/**
> + * axxia_i2c_empty_rx_fifo - Fetch data from RX FIFO and update SMBus block
> + * transfer length if this is the first byte of such a transfer.
> + */
> +static int
> +axxia_i2c_empty_rx_fifo(struct axxia_i2c_dev *idev)
> +{
> +	struct i2c_msg *msg = idev->msg;
> +	size_t rx_fifo_avail = readl(idev->base + MST_RX_FIFO);
> +	int bytes_to_transfer = min(rx_fifo_avail, msg->len - idev->msg_xfrd);
> +
> +	while (0 < bytes_to_transfer--) {

Please put constants on the right side. Reading this is very
twisting.

> +		int c = readl(idev->base + MST_DATA);
> +
> +		if (idev->msg_xfrd == 0 && i2c_m_recv_len(msg)) {
> +			/*
> +			 * Check length byte for SMBus block read
> +			 */
> +			if (c <= 0) {
> +				idev->msg_err = -EPROTO;
> +				i2c_int_disable(idev, ~0);
> +				complete(&idev->msg_complete);
> +				break;
> +			} else if (c > I2C_SMBUS_BLOCK_MAX) {
> +				c = I2C_SMBUS_BLOCK_MAX;

What about returning -EPROTO here as well? I don't think that reading
just a slice of all the data is helpful.

...

> +static irqreturn_t
> +axxia_i2c_isr(int irq, void *_dev)

Merge those into a single line please.

> +{
> +	struct axxia_i2c_dev *idev = _dev;
> +	u32 status;
> +
> +	if (!idev->msg)
> +		return IRQ_NONE;

This is actually not true. There might be interrupt bits set, so there
is an IRQ. There shouldn't be one, right, but that's another case IMO.

...

> +static int
> +axxia_i2c_xfer_msg(struct axxia_i2c_dev *idev, struct i2c_msg *msg)
> +{
> +	u32 int_mask = MST_STATUS_ERR | MST_STATUS_SNS;
> +	u32 rx_xfer, tx_xfer;
> +	u32 addr_1, addr_2;
> +	int ret;
> +
> +	if (msg->len == 0 || msg->len > 255)
> +		return -EINVAL;

Ouch, really? Maybe we should warn the user here.

> +
> +	idev->msg = msg;
> +	idev->msg_xfrd = 0;
> +	idev->msg_err = 0;
> +	init_completion(&idev->msg_complete);

reinit_completion?

> +	ret = wait_for_completion_timeout(&idev->msg_complete,
> +					  I2C_XFER_TIMEOUT);
> +
> +	i2c_int_disable(idev, int_mask);
> +
> +	WARN_ON(readl(idev->base + MST_COMMAND) & CMD_BUSY);
> +
> +	if (ret == 0) {
> +		dev_warn(idev->dev, "xfer timeout (%#x)\n", msg->addr);

But no warning here. Timeouts can easily happen.

> +		idev->msg_err = -ETIMEDOUT;
> +	}
> +
> +	if (unlikely(idev->msg_err))
> +		axxia_i2c_init(idev);
> +
> +	return idev->msg_err;
> +}
> +
> +static int
> +axxia_i2c_stop(struct axxia_i2c_dev *idev)
> +{
> +	u32 int_mask = MST_STATUS_ERR | MST_STATUS_SCC;
> +	int ret;
> +
> +	init_completion(&idev->msg_complete);

reinit_completion

> +
> +	/* Issue stop */
> +	writel(0xb, idev->base + MST_COMMAND);
> +	i2c_int_enable(idev, int_mask);
> +	ret = wait_for_completion_timeout(&idev->msg_complete,
> +					  I2C_STOP_TIMEOUT);
> +	i2c_int_disable(idev, int_mask);
> +	if (ret == 0)
> +		return -ETIMEDOUT;
> +
> +	WARN_ON(readl(idev->base + MST_COMMAND) & CMD_BUSY);

Message saying that bus is stuck should be enough? The call trace won't
help here.

...

> +#ifdef CONFIG_PM
> +static int axxia_i2c_suspend(struct platform_device *pdev, pm_message_t state)
> +{
> +	return -EOPNOTSUPP;
> +}
> +
> +static int axxia_i2c_resume(struct platform_device *pdev)
> +{
> +	return -EOPNOTSUPP;
> +}
> +#else
> +#define axxia_i2c_suspend NULL
> +#define axxia_i2c_resume NULL
> +#endif

Is this really better than to keep them empty?

> +static struct platform_driver axxia_i2c_driver = {
> +	.probe   = axxia_i2c_probe,
> +	.remove  = axxia_i2c_remove,
> +	.suspend = axxia_i2c_suspend,
> +	.resume  = axxia_i2c_resume,
> +	.driver  = {
> +		.name  = "axxia-i2c",
> +		.owner = THIS_MODULE,

owner can be dropped.

> +		.of_match_table = axxia_i2c_of_match,
> +	},
> +};
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