Re: [PATCH v1 2/2] i2c: microchip: Add driver for Microchip PolarFire SoC

[Wolfram Sang <wsa@kernel.org>]

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Hi Daire,

thanks for your driver! Some issues, but nothing major.

some checkpatch errors first:

ERROR: do not set execute permissions for source files
#47: FILE: drivers/i2c/busses/i2c-microchip.c

This must be fixed.


WARNING: added, moved or deleted file(s), does MAINTAINERS need updating?

Are you interested in maintaining the driver? Then, please add a section
to MAINTAINERS as well.

WARNING: From:/Signed-off-by: email address mismatch: 'From: Daire McNamara <Daire.McNamara@microchip.com>' != 'Signed-off-by: Daire McNamara <daire.mcnamara@microchip.com>'

Would be nice to have this consistent as well!


> +config I2C_MICROCHIP
> +	tristate "Microchip I2C"
> +	help
> +	  If you say yes to this option, support will be included for the
> +	  Microchip I2C interface.
> +

Document the module name?

> @@ -0,0 +1,519 @@
> +// SPDX-License-Identifier: GPL-2.0
> +/*
> + * Microchip I2C controller driver
> + *
> + * Copyright (c) 2018 - 2021 Microchip Corporation. All rights reserved.
> + *
> + * Author: Daire McNamara <daire.mcnamara@microchip.com>
> + */
> +#include <linux/clk.h>
> +#include <linux/clkdev.h>
> +#include <linux/err.h>
> +#include <linux/i2c.h>
> +#include <linux/iopoll.h>
> +#include <linux/interrupt.h>
> +#include <linux/module.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/platform_device.h>
> +
> +#define MICROCHIP_I2C_TIMEOUT (msecs_to_jiffies(1000))
> +
> +#define MPFS_I2C_CTRL				(0x00)
> +#define   CTRL_CR0				(0x00)
> +#define   CTRL_CR1				(0x01)
> +#define   CTRL_AA				(0x02)
> +#define   CTRL_SI				(0x03)
> +#define   CTRL_STO				(0x04)
> +#define   CTRL_STA				(0x05)
> +#define   CTRL_ENS1				(0x06)
> +#define   CTRL_CR2				(0x07)

Using the BIT() macros, this would remove a lot of "1 << " from the
driver and make it quite more readable, I'd say.

> +static int mpfs_i2c_init(struct mpfs_i2c_dev *idev)
> +{
> +	u32 clk_rate = clk_get_rate(idev->i2c_clk);
> +	u32 divisor = clk_rate / idev->bus_clk_rate;

Not protected against division by zero, or?

> +	u8 clkval;
> +	int ret;
> +	u8 ctrl = readl(idev->base + MPFS_I2C_CTRL);
> +
> +	ctrl &= ~CLK_MASK;
> +
> +	ret = mpfs_generate_divisor(divisor, &clkval);
> +
> +	if (ret)
> +		return -1;

-EINVAL instead of -1? In mpfs_generate_divisor as well.

> +
> +	ctrl |= clkval;
> +
> +	writel(ctrl, idev->base + MPFS_I2C_CTRL);
> +
> +	ctrl = readl(idev->base + MPFS_I2C_CTRL);
> +
> +	/* Reset controller */

Very obvious comment :)

> +	mpfs_i2c_reset(idev);
> +
> +	return 0;
> +}

> +static irqreturn_t mpfs_i2c_handle_isr(int irq, void *_dev)
> +{
> +	bool read, finish = false;

drivers/i2c/busses/i2c-microchip.c: In function ‘mpfs_i2c_handle_isr’:
drivers/i2c/busses/i2c-microchip.c:244:7: warning: variable ‘read’ set but not used [-Wunused-but-set-variable]

> +	struct mpfs_i2c_dev *idev = _dev;
> +	u32 status = idev->isr_status;
> +	u8 ctrl;
> +
> +	if (!idev->buf) {
> +		dev_warn(idev->dev, "unexpected interrupt\n");
> +		return IRQ_HANDLED;
> +	}
> +
> +	read = idev->msg_read ? 1 : 0;
> +
> +	switch (status) {
> +	case STATUS_M_START_SENT:
> +	case STATUS_M_REPEATED_START_SENT:
> +		ctrl = readl(idev->base + MPFS_I2C_CTRL);
> +		ctrl &= ~(1 << CTRL_STA);
> +		writel(idev->addr, idev->base + MPFS_I2C_DATA);
> +		writel(ctrl, idev->base + MPFS_I2C_CTRL);
> +		if (idev->msg_len <= 0)

    CPPCHECK
drivers/i2c/busses/i2c-microchip.c:263:21: warning: Checking if unsigned expression 'idev->msg_len' is less than zero. [unsignedLessThanZero]

...

> +static int mpfs_i2c_xfer_msg(struct mpfs_i2c_dev *idev, struct i2c_msg *msg)
> +{
> +	u8 ctrl;
> +	unsigned long time_left;
> +
> +	if (msg->len == 0)
> +		return -EINVAL;

Use a 'struct i2c_adapter_quirks' with the I2C_AQ_NO_ZERO_LEN flag and
the core will check that for you.

> +static u32 mpfs_i2c_func(struct i2c_adapter *adap)
> +{
> +	return I2C_FUNC_I2C | I2C_FUNC_SMBUS_EMUL;
> +}

If you can't do zero lenght transfers, you'll need
(I2C_FUNC_SMBUS_EMUL & ~I2C_FUNC_SMBUS_QUICK).

> +static int mpfs_i2c_probe(struct platform_device *pdev)
> +{
> +	struct mpfs_i2c_dev *idev = NULL;

Initialization not needed.

> +	idev->dev = &pdev->dev;
> +	init_completion(&idev->msg_complete);
> +	spin_lock_init(&idev->lock);

This spinlock is not used anywhere? It seems that everything spinlock
related can go?

> +
> +	val = device_property_read_u32(idev->dev, "clock-frequency",
> +				       &idev->bus_clk_rate);
> +	if (val) {
> +		dev_info(&pdev->dev, "default to 100kHz\n");
> +		idev->bus_clk_rate = 100000;	/* default clock rate */
> +	}
> +
> +	if (idev->bus_clk_rate > 400000) {
> +		dev_err(&pdev->dev, "invalid clock-frequency %d\n",
> +			idev->bus_clk_rate);
> +		return -EINVAL;
> +	}
> +
> +	ret = devm_request_irq(&pdev->dev, irq, mpfs_i2c_isr,
> +			       IRQF_SHARED, pdev->name, idev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to claim irq %d\n", irq);
> +		return ret;
> +	}
> +
> +	ret = clk_prepare_enable(idev->i2c_clk);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to enable clock\n");
> +		return ret;
> +	}
> +
> +	ret = mpfs_i2c_init(idev);
> +	if (ret) {
> +		dev_err(&pdev->dev, "failed to program clock divider\n");
> +		return ret;
> +	}
> +
> +	i2c_set_adapdata(&idev->adapter, idev);
> +	snprintf(idev->adapter.name, sizeof(idev->adapter.name),
> +		 "Microchip I2C hw bus");

Most people add the base address of the registers here to be able to
differentiate multiple adapters in one system.

> +	idev->adapter.owner = THIS_MODULE;
> +	idev->adapter.algo = &mpfs_i2c_algo;
> +	idev->adapter.dev.parent = &pdev->dev;
> +	idev->adapter.dev.of_node = pdev->dev.of_node;
> +
> +	platform_set_drvdata(pdev, idev);
> +
> +	ret = i2c_add_adapter(&idev->adapter);
> +	if (ret) {
> +		clk_disable_unprepare(idev->i2c_clk);
> +		return ret;
> +	}
> +
> +	dev_info(&pdev->dev, "Microchip I2C Probe Complete\n");
> +
> +	return 0;
> +}

But this is all pretty minor stuff. It looks quite good actually!

Happy hacking,

   Wolfram


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