[PATCH v4 3/3] i2c: stm32f7: support i2c_*_dma_safe_msg_buf APIs

Clément Le Goffic
2025-07-04T08:42:01Z

`i2c_*_dma_safe_msg_buf` APIs operate on a `struct i2c_msg`.
The get operation make sure the I2C buffer is DMA'able according to its
buffer length, or if the memory use is DMA coherent for example and
return a valid pointer for safe DMA access to be used.
The put operation release the pointer.
Prefer using generic API's than relying on private tests.

Acked-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Clément Le Goffic <clement.legoffic@foss.st.com>
---
drivers/i2c/busses/i2c-stm32f7.c | 32 +++++++++++++++++++++-----------
1 file changed, 21 insertions(+), 11 deletions(-)

diff --git a/drivers/i2c/busses/i2c-stm32f7.c b/drivers/i2c/busses/i2c-stm32f7.c
index 73a7b8894c0d..994232646789 100644
--- a/drivers/i2c/busses/i2c-stm32f7.c
+++ b/drivers/i2c/busses/i2c-stm32f7.c
@@ -741,11 +741,14 @@ static void stm32f7_i2c_dma_callback(void *arg)
{
struct stm32f7_i2c_dev *i2c_dev = arg;
struct stm32_i2c_dma *dma = i2c_dev->dma;
+ struct stm32f7_i2c_msg *f7_msg = &i2c_dev->f7_msg;

stm32f7_i2c_disable_dma_req(i2c_dev);
dmaengine_terminate_async(dma->chan_using);
dma_unmap_single(i2c_dev->dev, dma->dma_buf, dma->dma_len,
dma->dma_data_dir);
+ if (!f7_msg->smbus)
+ i2c_put_dma_safe_msg_buf(f7_msg->buf, i2c_dev->msg, true);
complete(&dma->dma_complete);
}

@@ -881,6 +884,7 @@ static void stm32f7_i2c_xfer_msg(struct stm32f7_i2c_dev *i2c_dev,
{
struct stm32f7_i2c_msg *f7_msg = &i2c_dev->f7_msg;
void __iomem *base = i2c_dev->base;
+ u8 *dma_buf;
u32 cr1, cr2;
int ret;

@@ -930,17 +934,23 @@ static void stm32f7_i2c_xfer_msg(struct stm32f7_i2c_dev *i2c_dev,

/* Configure DMA or enable RX/TX interrupt */
i2c_dev->use_dma = false;
- if (i2c_dev->dma && f7_msg->count >= STM32F7_I2C_DMA_LEN_MIN
- && !i2c_dev->atomic) {
- ret = stm32_i2c_prep_dma_xfer(i2c_dev->dev, i2c_dev->dma,
- msg->flags & I2C_M_RD,
- f7_msg->count, f7_msg->buf,
- stm32f7_i2c_dma_callback,
- i2c_dev);
- if (!ret)
- i2c_dev->use_dma = true;
- else
- dev_warn(i2c_dev->dev, "can't use DMA\n");
+ if (i2c_dev->dma && !i2c_dev->atomic) {
+ dma_buf = i2c_get_dma_safe_msg_buf(msg, STM32F7_I2C_DMA_LEN_MIN);
+ if (dma_buf) {
+ f7_msg->buf = dma_buf;
+ ret = stm32_i2c_prep_dma_xfer(i2c_dev->dev, i2c_dev->dma,
+ msg->flags & I2C_M_RD,
+ f7_msg->count, f7_msg->buf,
+ stm32f7_i2c_dma_callback,
+ i2c_dev);
+ if (ret) {
+ dev_warn(i2c_dev->dev, "can't use DMA\n");
+ i2c_put_dma_safe_msg_buf(f7_msg->buf, msg, false);
+ f7_msg->buf = msg->buf;
+ } else {
+ i2c_dev->use_dma = true;
+ }
+ }
}

if (!i2c_dev->use_dma) {

--
2.43.0