Hi Wolfram,
On 2017-07-18 12:23:36 +0200, Wolfram Sang 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@xxxxxxxxxxxxxxxxxxxx>
Reviewed-by: Niklas Söderlund <niklas.soderlund+renesas@xxxxxxxxxxxx>
> ---
> Changes since v2:
>
> * rebased to v4.13-rc1
> * helper functions are not inlined anymore but moved to i2c core
> * __must_check has been added to the buffer check helper
> * the release function has been renamed to contain 'dma' as well
>
> drivers/i2c/i2c-core-base.c | 68 +++++++++++++++++++++++++++++++++++++++++++++
> include/linux/i2c.h | 5 ++++
> 2 files changed, 73 insertions(+)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index c89dac7fd2e7b7..7326a9d2e4eb69 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -34,6 +34,7 @@
> #include <linux/irqflags.h>
> #include <linux/jump_label.h>
> #include <linux/kernel.h>
> +#include <linux/mm.h>
> #include <linux/module.h>
> #include <linux/mutex.h>
> #include <linux/of_device.h>
> @@ -44,6 +45,7 @@
> #include <linux/pm_wakeirq.h>
> #include <linux/property.h>
> #include <linux/rwsem.h>
> +#include <linux/sched/task_stack.h>
> #include <linux/slab.h>
>
> #include "i2c-core.h"
> @@ -2240,6 +2242,72 @@ void i2c_put_adapter(struct i2c_adapter *adap)
> }
> EXPORT_SYMBOL(i2c_put_adapter);
>
> +/**
> + * i2c_check_msg_for_dma() - check if a message is suitable for DMA
> + * @msg: the message to be checked
> + * @threshold: the amount of byte from which using DMA makes sense
> + * @ptr_for_bounce_buf: if not NULL, a bounce buffer will be attached to this
> + * ptr, if needed. The bounce buffer must be freed by the
> + * caller using i2c_release_dma_bounce_buf().
> + *
> + * Return: -ERANGE if message is smaller than threshold
> + * -EFAULT if message buffer is not DMA capable and no bounce buffer
> + * was requested
> + * -ENOMEM if a bounce buffer could not be created
> + * 0 if message is suitable for DMA
> + *
> + * The return value must be checked.
> + *
> + * Note: This function should only be called from process context! It uses
> + * helper functions which work on the 'current' task.
> + */
> +int i2c_check_msg_for_dma(struct i2c_msg *msg, unsigned int threshold,
> + u8 **ptr_for_bounce_buf)
> +{
> + if (ptr_for_bounce_buf)
> + *ptr_for_bounce_buf = NULL;
> +
> + if (msg->len < threshold)
> + return -ERANGE;
> +
> + if (!virt_addr_valid(msg->buf) || object_is_on_stack(msg->buf)) {
> + pr_debug("msg buffer to 0x%04x is not DMA safe%s\n", msg->addr,
> + ptr_for_bounce_buf ? ", trying bounce buffer" : "");
> + if (ptr_for_bounce_buf) {
> + if (msg->flags & I2C_M_RD)
> + *ptr_for_bounce_buf = kzalloc(msg->len, GFP_KERNEL);
> + else
> + *ptr_for_bounce_buf = kmemdup(msg->buf, msg->len,
> + GFP_KERNEL);
> + if (!*ptr_for_bounce_buf)
> + return -ENOMEM;
> + } else {
> + return -EFAULT;
> + }
> + }
> +
> + return 0;
> +}
> +EXPORT_SYMBOL_GPL(i2c_check_msg_for_dma);
> +
> +/**
> + * i2c_release_bounce_buf - copy data back from bounce buffer and release it
> + * @msg: the message to be copied back to
> + * @bounce_buf: the bounce buffer obtained from i2c_check_msg_for_dma().
> + * May be NULL.
> + */
> +void i2c_release_dma_bounce_buf(struct i2c_msg *msg, u8 *bounce_buf)
> +{
> + if (!bounce_buf)
> + return;
> +
> + if (msg->flags & I2C_M_RD)
> + memcpy(msg->buf, bounce_buf, msg->len);
> +
> + kfree(bounce_buf);
> +}
> +EXPORT_SYMBOL_GPL(i2c_release_bounce_buf);
> +
> MODULE_AUTHOR("Simon G. Vogl <simon@xxxxxxxxxxxxxxxxx>");
> MODULE_DESCRIPTION("I2C-Bus main module");
> MODULE_LICENSE("GPL");
> diff --git a/include/linux/i2c.h b/include/linux/i2c.h
> index 00ca5b86a753f8..ac02287b6c0d8f 100644
> --- a/include/linux/i2c.h
> +++ b/include/linux/i2c.h
> @@ -766,6 +766,11 @@ static inline u8 i2c_8bit_addr_from_msg(const struct i2c_msg *msg)
> return (msg->addr << 1) | (msg->flags & I2C_M_RD ? 1 : 0);
> }
>
> +int __must_check i2c_check_msg_for_dma(struct i2c_msg *msg, unsigned int threshold,
> + u8 **ptr_for_bounce_buf);
> +
> +void i2c_release_dma_bounce_buf(struct i2c_msg *msg, u8 *bounce_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
> --
> 2.11.0
>
--
Regards,
Niklas Söderlund
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