arch: cxd56xx: Fix deadlock by using GNSS CEP file on SPI-Flash

If you specify a file path on SPI-Flash in CONFIG_CXD56_GNSS_CEP_FILENAME,
it causes a deadlock issue in the inter-CPU communication. To resolve it,
introduce a new CONFIG_CXD56_GNSS_CEP_ON_SPIFLASH and then use pre-read
buffers during checking CEP file. So this needs the large of free memory.

arch/arm/src/cxd56xx/Kconfig

@@ -1312,6 +1312,12 @@ config CXD56_GNSS_CEP_FILENAME
 	---help---
 		Specify the path and file name of cep data.
 
+config CXD56_GNSS_CEP_ON_SPIFLASH
+	bool "GNSS CEP file on SPI-Flash"
+	default n
+	---help---
+		Use a cep file on SPI-Flash.
+
 config CXD56_GNSS_FW_RTK
 	bool "Support carrier-phase data output for Real-Time Kinematic"
 	default n

arch/arm/src/cxd56xx/cxd56_gnss.c

@@ -32,6 +32,7 @@
 #include <poll.h>
 #include <errno.h>
 #include <debug.h>
+#include <sys/stat.h>
 
 #include <nuttx/kmalloc.h>
 #include <nuttx/mutex.h>
@@ -394,6 +395,14 @@ static struct pm_cpu_freqlock_s g_lv_lock =
 static struct pm_cpu_freqlock_s g_hold_lock =
   PM_CPUFREQLOCK_INIT(0, PM_CPUFREQLOCK_FLAG_HOLD);
 
+#ifdef CONFIG_CXD56_GNSS_CEP_ON_SPIFLASH
+/* Buffer and length for CEP data on SPI-Flash */
+
+static int    g_check_cep_flag = 0;
+static char  *g_cepdata = NULL;
+static size_t g_ceplen = 0;
+#endif
+
 /****************************************************************************
  * Private Functions
  ****************************************************************************/
@@ -1013,6 +1022,82 @@ static int cxd56_gnss_close_cep_data(struct file *filep,
  *   Zero (OK) on success; a negated errno value on failure.
  *
  ****************************************************************************/
+#ifdef CONFIG_CXD56_GNSS_CEP_ON_SPIFLASH
+static int cxd56_gnss_check_cep_data(struct file *filep, unsigned long arg)
+{
+  int ret;
+  struct stat statbuf;
+  struct inode *inode;
+  struct cxd56_gnss_dev_s *priv;
+
+  inode = filep->f_inode;
+  priv  = (struct cxd56_gnss_dev_s *)inode->i_private;
+
+  /* Set a flag for checking CEP data  */
+
+  g_check_cep_flag = 1;
+
+  /* Allocate a buffer and read all of CEP data to it */
+
+  g_cepdata = NULL;
+  g_ceplen = 0;
+
+  ret = file_fstat(&priv->cepfp, &statbuf);
+  if (ret == 0)
+    {
+      g_ceplen = (size_t)statbuf.st_size;
+    }
+  else
+    {
+      return ret;
+    }
+
+  if (g_ceplen > 0)
+    {
+      g_cepdata = (char *)kmm_malloc(g_ceplen);
+    }
+
+  if (!g_cepdata)
+    {
+      gnsserr("Failed to allocate cep data\n");
+      return -ENOMEM;
+    }
+
+  /* Set the file position to the beginning before reading */
+
+  ret = file_seek(&priv->cepfp, 0, SEEK_SET);
+  if (ret < 0)
+    {
+      goto errout;
+    }
+
+  ret = file_read(&priv->cepfp, g_cepdata, g_ceplen);
+  if (ret < 0)
+    {
+      goto errout;
+    }
+
+  ret = fw_gd_cepcheckassistdata();
+
+errout:
+
+  /* Free an allocated buffer */
+
+  if (g_cepdata)
+    {
+      kmm_free(g_cepdata);
+      g_cepdata = NULL;
+      g_ceplen = 0;
+    }
+
+  /* Clear a flag for checking CEP data  */
+
+  g_check_cep_flag = 0;
+
+  return ret;
+}
+
+#else /* !CONFIG_CXD56_GNSS_CEP_ON_SPIFLASH */
 
 static int cxd56_gnss_check_cep_data(struct file *filep,
                                      unsigned long arg)
@@ -1020,6 +1105,8 @@ static int cxd56_gnss_check_cep_data(struct file *filep,
   return fw_gd_cepcheckassistdata();
 }
 
+#endif
+
 /****************************************************************************
  * Name: cxd56_gnss_get_cep_age
  *
@@ -2136,6 +2223,27 @@ cxd56_gnss_read_cep_file(struct file *fp, int32_t offset,
   char *buf;
   int   ret;
 
+#ifdef CONFIG_CXD56_GNSS_CEP_ON_SPIFLASH
+  if (g_check_cep_flag)
+    {
+      /* If checking CEP data, use a pre-read buffer in advance */
+
+      if (offset + len > g_ceplen)
+        {
+          ret = -ENOENT;
+          goto _err0;
+        }
+
+      buf = &g_cepdata[offset];
+
+      *retval = len;
+
+      cxd56_cpu1sigsend(CXD56_CPU1_DATA_TYPE_CEP, (uint32_t)buf);
+
+      return NULL;
+    }
+#endif
+
   if (fp == NULL)
     {
       ret = -ENOENT;