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SubjectRe: [RFC PATCH v5 2/6] i2c: add helpers to ease DMA handling
On Wed, 20 Sep 2017 20:59:52 +0200
Wolfram Sang <wsa+renesas@sang-engineering.com> wrote:

> One helper checks if DMA is suitable and optionally creates a bounce
> buffer, if not. The other function returns the bounce buffer and makes
> sure the data is properly copied back to the message.
>
> Signed-off-by: Wolfram Sang <wsa+renesas@sang-engineering.com>

One minor suggestion for wording. Otherwise looks good to me.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

> ---
> drivers/i2c/i2c-core-base.c | 45 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/i2c.h | 3 +++
> 2 files changed, 48 insertions(+)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 56e46581b84bdb..925a22794d3ced 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -2241,6 +2241,51 @@ void i2c_put_adapter(struct i2c_adapter *adap)
> }
> EXPORT_SYMBOL(i2c_put_adapter);
>
> +/**
> + * i2c_get_dma_safe_msg_buf() - get a DMA safe buffer for the given i2c_msg
> + * @msg: the message to be checked
> + * @threshold: the amount of byte from which using DMA makes sense

the minimum number of bytes for which using DMA makes sense.

> + *
> + * Return: NULL if a DMA safe buffer was not obtained. Use msg->buf with PIO.
> + *
> + * Or a valid pointer to be used with DMA. Note that it can either be
> + * msg->buf or a bounce buffer. After use, release it by calling
> + * i2c_release_dma_safe_msg_buf().
> + *
> + * This function must only be called from process context!
> + */
> +u8 *i2c_get_dma_safe_msg_buf(struct i2c_msg *msg, unsigned int threshold)
> +{
> + if (msg->len < threshold)
> + return NULL;
> +
> + if (msg->flags & I2C_M_DMA_SAFE)
> + return msg->buf;
> +
> + if (msg->flags & I2C_M_RD)
> + return kzalloc(msg->len, GFP_KERNEL);
> + else
> + return kmemdup(msg->buf, msg->len, GFP_KERNEL);
> +}
> +EXPORT_SYMBOL_GPL(i2c_get_dma_safe_msg_buf);
> +
> +/**
> + * i2c_release_dma_safe_msg_buf - release DMA safe buffer and sync with i2c_msg
> + * @msg: the message to be synced with
> + * @buf: the buffer obtained from i2c_get_dma_safe_msg_buf(). May be NULL.
> + */
> +void i2c_release_dma_safe_msg_buf(struct i2c_msg *msg, u8 *buf)
> +{
> + if (!buf || buf == msg->buf)
> + return;
> +
> + if (msg->flags & I2C_M_RD)
> + memcpy(msg->buf, buf, msg->len);
> +
> + kfree(buf);
> +}
> +EXPORT_SYMBOL_GPL(i2c_release_dma_safe_msg_buf);
> +
> MODULE_AUTHOR("Simon G. Vogl <simon@tk.uni-linz.ac.at>");
> MODULE_DESCRIPTION("I2C-Bus main module");
> MODULE_LICENSE("GPL");
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index d501d3956f13f0..1e99342f180f45 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -767,6 +767,9 @@ static inline u8 i2c_8bit_addr_from_msg(const struct i2c_msg *msg)
> return (msg->addr << 1) | (msg->flags & I2C_M_RD ? 1 : 0);
> }
>
> +u8 *i2c_get_dma_safe_msg_buf(struct i2c_msg *msg, unsigned int threshold);
> +void i2c_release_dma_safe_msg_buf(struct i2c_msg *msg, u8 *buf);
> +
> int i2c_handle_smbus_host_notify(struct i2c_adapter *adap, unsigned short addr);
> /**
> * module_i2c_driver() - Helper macro for registering a modular I2C driver

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