linux-kernel - Re: [PATCH v2] i2c: at91: support atomic write xfer

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Message-ID: <c789352c-5517-1fd9-980d-f8f6c2017901@gmail.com>
Date:   Sun, 22 Mar 2020 04:39:58 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Michał Mirosław <mirq-linux@...e.qmqm.pl>,
        Ludovic Desroches <ludovic.desroches@...rochip.com>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>
Cc:     Stefan Lengfeld <contact@...fanchrist.eu>,
        Marco Felsch <m.felsch@...gutronix.de>,
        linux-i2c@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] i2c: at91: support atomic write xfer

22.03.2020 00:03, Michał Mirosław пишет:
> Implement basic support for atomic write - enough to get a simple
> write to PMIC on shutdown. Only for chips having ALT_CMD register,
> eg. SAMA5D2.
> 
> Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> ---
> v2: remove runtime-PM usage
>     switch to readl*poll*atomic() for transfer completion wait
> ---
>  drivers/i2c/busses/i2c-at91-master.c | 69 +++++++++++++++++++++++++++-
>  1 file changed, 67 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/i2c/busses/i2c-at91-master.c b/drivers/i2c/busses/i2c-at91-master.c
> index ba6fbb9c7390..d9226207157a 100644
> --- a/drivers/i2c/busses/i2c-at91-master.c
> +++ b/drivers/i2c/busses/i2c-at91-master.c
> @@ -21,6 +21,7 @@
>  #include <linux/i2c.h>
>  #include <linux/interrupt.h>
>  #include <linux/io.h>
> +#include <linux/iopoll.h>
>  #include <linux/of.h>
>  #include <linux/of_device.h>
>  #include <linux/platform_device.h>
> @@ -709,6 +710,69 @@ static int at91_twi_xfer(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
>  	return ret;
>  }
>  
> +static int at91_twi_xfer_atomic(struct i2c_adapter *adap, struct i2c_msg *msg, int num)
> +{
> +	struct at91_twi_dev *dev = i2c_get_adapdata(adap);
> +	unsigned long timeout;
> +	struct pinctrl *pins;
> +	__u32 stat;
> +	int ret;
> +
> +	/* FIXME: only single write request supported to 7-bit addr */
> +	if (num != 1)
> +		return -EOPNOTSUPP;
> +	if (msg->flags & I2C_M_RD)
> +		return -EOPNOTSUPP;
> +	if (msg->flags & I2C_M_TEN)
> +		return -EOPNOTSUPP;
> +	if (msg->len > dev->fifo_size && msg->len > 1)
> +		return -EOPNOTSUPP;
> +	if (!dev->pdata->has_alt_cmd)
> +		return -EOPNOTSUPP;
> +
> +	pins = pinctrl_get_select_default(&adap->dev);
> +
> +	ret = clk_prepare_enable(twi_dev->clk);

Hello Michał,

Please see comments to the clk_prepare_enable() and clk_prepare().

/* clk_prepare_enable helps cases using clk_enable in non-atomic context. */
static inline int clk_prepare_enable(struct clk *clk)
...
 * clk_prepare may sleep, which differentiates it from clk_enable.