arch/imx9_lpspi: Use DMA safe buffers to do the DMA transfers

Using user allocated buffers for DMA transfers is not safe for two reasons:
- User space memory is virtual memory, DMA needs physical memory
- User memory buffer alignment cannot be guaranteed -> cache line ops
  are not safe

arch/arm64/src/imx9/Kconfig

@@ -722,6 +722,13 @@ config IMX9_LPSPI_DMATHRESHOLD
  by polling logic. But we need a threshold value to determine what
  is small.
 
+config IMX9_LPSPI_DMA_BUFFER_SIZE
+ int "LPSPI DMA buffer size"
+ default 4096
+ depends on IMX9_LPSPI_DMA
+ ---help---
+ Set the LPSPI driver DMA buffer size.
+
 config IMX9_LPSPI1_DMA
  bool "LPSPI1 DMA"
  default n

arch/arm64/src/imx9/imx9_lpspi.c

@@ -67,6 +67,7 @@
 #include "arm64_internal.h"
 #include "imx9_ccm.h"
 #include "imx9_clockconfig.h"
+#include "imx9_dma_alloc.h"
 #include "imx9_gpio.h"
 #include "imx9_iomuxc.h"
 #include "imx9_lpspi.h"
@@ -131,6 +132,8 @@ struct imx9_lpspidev_s
  DMACH_HANDLE txdma; /* DMA channel handle for TX transfers */
  sem_t rxsem; /* Wait for RX DMA to complete */
  sem_t txsem; /* Wait for TX DMA to complete */
+ void *txbuf; /* Driver DMA safe buffer for TX */
+ void *rxbuf; /* Driver DMA safe buffer for RX */
 #endif
 };
 
@@ -1305,13 +1308,13 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
  const void *txbuffer,
  void *rxbuffer, size_t nwords)
 {
+ struct imx9_lpspidev_s *priv = (struct imx9_lpspidev_s *)dev;
  int ret;
  size_t adjust;
  ssize_t nbytes;
  static uint8_t rxdummy[4] aligned_data(4);
  static const uint16_t txdummy = 0xffff;
  uint32_t regval;
- struct imx9_lpspidev_s *priv = (struct imx9_lpspidev_s *)dev;
 
  DEBUGASSERT(priv != NULL);
  DEBUGASSERT(priv && priv->spibase);
@@ -1338,6 +1341,17 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
  return;
  }
 
+ /* Check if the transfer is too long */
+
+ if (nbytes > CONFIG_IMX9_LPSPI_DMA_BUFFER_SIZE)
+ {
+ /* Transfer is too long, revert to slow non-DMA method */
+
+ spiwarn("frame %lu too long, fall back to no DMA transfer\n", nbytes);
+ imx9_lpspi_exchange_nodma(dev, txbuffer, rxbuffer, nwords);
+ return;
+ }
+
  /* Disable SPI when we are configuring it */
 
  imx9_lpspi_modifyreg32(priv, IMX9_LPSPI_CR_OFFSET, LPSPI_CR_MEN, 0);
@@ -1362,13 +1376,22 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
 
  if (txbuffer)
  {
- up_clean_dcache((uintptr_t)txbuffer, (uintptr_t)txbuffer + nbytes);
+ /* Move the user data to device internal buffer */
+
+ memcpy(priv->txbuf, txbuffer, nbytes);
+
+ /* And flush it to RAM */
+
+ up_clean_dcache((uintptr_t)priv->txbuf,
+ (uintptr_t)priv->txbuf + nbytes);
  }
 
  if (rxbuffer)
  {
- up_invalidate_dcache((uintptr_t)rxbuffer,
- (uintptr_t)rxbuffer + nbytes);
+ /* Prepare the RX buffer for DMA */
+
+ up_invalidate_dcache((uintptr_t)priv->rxbuf,
+ (uintptr_t)priv->rxbuf + nbytes);
  }
 
  /* Set up the DMA */
@@ -1378,7 +1401,7 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
  struct imx9_edma_xfrconfig_s config;
 
  config.saddr = priv->spibase + IMX9_LPSPI_RDR_OFFSET;
- config.daddr = (uintptr_t) (rxbuffer ? rxbuffer : rxdummy);
+ config.daddr = (uintptr_t) (rxbuffer ? priv->rxbuf : rxdummy);
  config.soff = 0;
  config.doff = rxbuffer ? adjust : 0;
  config.iter = nbytes;
@@ -1391,7 +1414,7 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
 #endif
  imx9_dmach_xfrsetup(priv->rxdma, &config);
 
- config.saddr = (uintptr_t) (txbuffer ? txbuffer : &txdummy);
+ config.saddr = (uintptr_t) (txbuffer ? priv->txbuf : &txdummy);
  config.daddr = priv->spibase + IMX9_LPSPI_TDR_OFFSET;
  config.soff = txbuffer ? adjust : 0;
  config.doff = 0;
@@ -1436,10 +1459,16 @@ static void imx9_lpspi_exchange(struct spi_dev_s *dev,
 
  imx9_lpspi_putreg32(priv, IMX9_LPSPI_DER_OFFSET, 0);
 
- if (rxbuffer)
+ if (rxbuffer && ret >= 0)
  {
- up_invalidate_dcache((uintptr_t)rxbuffer,
- (uintptr_t)rxbuffer + nbytes);
+ /* Flush the RX data to ram */
+
+ up_invalidate_dcache((uintptr_t)priv->rxbuf,
+ (uintptr_t)priv->rxbuf + nbytes);
+
+ /* Copy data to user buffer */
+
+ memcpy(rxbuffer, priv->rxbuf, nbytes);
  }
 }
 
@@ -2044,6 +2073,13 @@ struct spi_dev_s *imx9_lpspibus_initialize(int bus)
  priv->rxdma = imx9_dmach_alloc(priv->rxch, 0);
  DEBUGASSERT(priv->rxdma && priv->txdma);
  }
+
+ if (priv->txbuf == NULL && priv->rxbuf == NULL)
+ {
+ priv->txbuf = imx9_dma_alloc(CONFIG_IMX9_LPSPI_DMA_BUFFER_SIZE);
+ priv->rxbuf = imx9_dma_alloc(CONFIG_IMX9_LPSPI_DMA_BUFFER_SIZE);
+ DEBUGASSERT(priv->txbuf && priv->rxbuf);
+ }
  }
  else
  {