i2c: stm32f7: support i2c_*_dma_safe_msg_buf APIs

`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>
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>
Link: https://lore.kernel.org/r/20250704-i2c-upstream-v4-3-84a095a2c728@foss.st.com

Author: clegoffic

drivers/i2c/busses/i2c-stm32f7.c

@@ -742,11 +742,14 @@ 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);
 }
 
@@ -882,6 +885,7 @@ 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;
 
@@ -931,17 +935,23 @@ 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) {