Re: [PATCH 2/2] i2c: New bus driver for the QUP I2C controller

[Josh Cartwright <joshc@codeaurora.org>]

Hey Ivan-

Some nits below.

On Thu, Aug 29, 2013 at 04:27:53PM +0300, Ivan T. Ivanov wrote:
> From: "Ivan T. Ivanov" <iivanov@mm-sol.com>
> 
> This bus driver supports the QUP i2c hardware controller in the Qualcomm
> MSM SOCs.  The Qualcomm Universal Peripheral Engine (QUP) is a general
> purpose data path engine with input/output FIFOs and an embedded i2c
> mini-core. The driver supports FIFO mode (for low bandwidth	applications)

Rogue tab in your commit message.

> and block mode (interrupt generated for each block-size data transfer).
> The driver currently does not support DMA transfers.
> 
> Shamelessly based on codeaurora version of the driver.
> 
> This controller could be found in the following chip-sets:
> msm9625, msm8974, msm8610, msm8226, mpq8092.

This may be good to include in the Kconfig help text.

> Signed-off-by: Ivan T. Ivanov <iivanov@mm-sol.com>
> ---
>  drivers/i2c/busses/Kconfig   |   10 +
>  drivers/i2c/busses/Makefile  |    1 +
>  drivers/i2c/busses/i2c-qup.c |  909 ++++++++++++++++++++++++++++++++++++++++++
>  3 files changed, 920 insertions(+)
>  create mode 100644 drivers/i2c/busses/i2c-qup.c
> 
> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
> index fcdd321..c76ddd4 100644
> --- a/drivers/i2c/busses/Kconfig
> +++ b/drivers/i2c/busses/Kconfig
> @@ -777,6 +777,16 @@ config I2C_RCAR
>  	  This driver can also be built as a module.  If so, the module
>  	  will be called i2c-rcar.
>  
> +config I2C_QUP
> +	tristate "Qualcomm QUP based I2C controller"
> +	depends on ARCH_MSM
> +	help
> +	  If you say yes to this option, support will be included for the
> +	  built-in I2C interface on the MSM family processors.
> +
> +	  This driver can also be built as a module.  If so, the module
> +	  will be called i2c-qup.
> +
>  comment "External I2C/SMBus adapter drivers"
>  
>  config I2C_DIOLAN_U2C
> diff --git a/drivers/i2c/busses/Makefile b/drivers/i2c/busses/Makefile
> index d00997f..77127df 100644
> --- a/drivers/i2c/busses/Makefile
> +++ b/drivers/i2c/busses/Makefile
> @@ -76,6 +76,7 @@ obj-$(CONFIG_I2C_OCTEON)	+= i2c-octeon.o
>  obj-$(CONFIG_I2C_XILINX)	+= i2c-xiic.o
>  obj-$(CONFIG_I2C_XLR)		+= i2c-xlr.o
>  obj-$(CONFIG_I2C_RCAR)		+= i2c-rcar.o
> +obj-$(CONFIG_I2C_QUP)		+= i2c-qup.o
>  
>  # External I2C/SMBus adapter drivers
>  obj-$(CONFIG_I2C_DIOLAN_U2C)	+= i2c-diolan-u2c.o
> diff --git a/drivers/i2c/busses/i2c-qup.c b/drivers/i2c/busses/i2c-qup.c
> new file mode 100644
> index 0000000..3b5ef91
> --- /dev/null
> +++ b/drivers/i2c/busses/i2c-qup.c
[..]
> +
> +static int qup_i2c_change_state(struct qup_i2c_dev *qup, u32 state)
> +{
> +	if (qup_i2c_poll_state(qup, 0, true) != 0)
> +		return -EIO;
> +
> +	writel(state, qup->base + QUP_STATE);
> +
> +	if (qup_i2c_poll_state(qup, state, false) != 0)
> +		return -EIO;
> +	return 0;
> +}
> +
> +static void qup_i2c_enable(struct qup_i2c_dev *qup, bool state)

Bit of a confusing name, especially when qup_i2c_enable(qup, false) is
used. I'd suggest qup_i2c_set_state or qup_i2c_set_enabled.

> +{
> +	u32 config;
> +
> +	if (state) {
> +		clk_prepare_enable(qup->clk);
> +		clk_prepare_enable(qup->pclk);
> +	} else {
> +		qup_i2c_change_state(qup, QUP_RESET_STATE);
> +		clk_disable_unprepare(qup->clk);
> +		config = readl(qup->base + QUP_CONFIG);
> +		config |= QUP_CLOCK_AUTO_GATE;
> +		writel(config, qup->base + QUP_CONFIG);
> +		clk_disable_unprepare(qup->pclk);
> +	}
> +}
[..]
> +static int qup_i2c_probe(struct platform_device *pdev)
> +{
[..]
> +
> +	ret = devm_request_irq(qup->dev, qup->irq, qup_i2c_interrupt,
> +			       IRQF_TRIGGER_HIGH, "i2c_qup", qup);
> +	if (ret) {
> +		dev_err(qup->dev, "Request %d IRQ failed\n", qup->irq);
> +		return ret;
> +	}
> +
> +	disable_irq(qup->irq);

How is this not racy, in the case where a pending interrupt is left from
the bootloader (which seems to be possible based on the comments below)?

> +
> +	init_completion(&qup->xfer);
> +
> +	ret = clk_set_rate(qup->clk, qup->src_clk_freq);
> +	if (ret)
> +		dev_info(qup->dev, "Fail to set core clk, %dHz:%d\n",
> +			 qup->src_clk_freq, ret);
> +
> +	qup_i2c_enable(qup, true);
> +
> +	/*
> +	 * If bootloaders leave a pending interrupt on certain QUP's,
> +	 * then we reset the core before registering for interrupts.
> +	 */
[..]

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