feat(mtd): add platform function to allow using external buffer

The scratch buffer could be large. The new function allows
platform to defined its own external buffer or use the default
one.

Signed-off-by: Lionel Debieve <lionel.debieve@foss.st.com>
Change-Id: Ib7ab8ff19fa0a9cb06e364f058b91af58c3c471a
diff --git a/drivers/mtd/nand/core.c b/drivers/mtd/nand/core.c
index 9f0331a..6ef2256 100644
--- a/drivers/mtd/nand/core.c
+++ b/drivers/mtd/nand/core.c
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2019-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -8,18 +8,29 @@
 #include <errno.h>
 #include <stddef.h>
 
-#include <platform_def.h>
-
 #include <common/debug.h>
 #include <drivers/delay_timer.h>
 #include <drivers/nand.h>
 #include <lib/utils.h>
 
+#include <platform_def.h>
+
 /*
  * Define a single nand_device used by specific NAND frameworks.
  */
 static struct nand_device nand_dev;
-static uint8_t scratch_buff[PLATFORM_MTD_MAX_PAGE_SIZE];
+
+#pragma weak plat_get_scratch_buffer
+void plat_get_scratch_buffer(void **buffer_addr, size_t *buf_size)
+{
+	static uint8_t scratch_buff[PLATFORM_MTD_MAX_PAGE_SIZE];
+
+	assert(buffer_addr != NULL);
+	assert(buf_size != NULL);
+
+	*buffer_addr = (void *)scratch_buff;
+	*buf_size = sizeof(scratch_buff);
+}
 
 int nand_read(unsigned int offset, uintptr_t buffer, size_t length,
 	      size_t *length_read)
@@ -34,6 +45,12 @@
 	unsigned int bytes_read;
 	int is_bad;
 	int ret;
+	uint8_t *scratch_buff;
+	size_t scratch_buff_size;
+
+	plat_get_scratch_buffer((void **)&scratch_buff, &scratch_buff_size);
+
+	assert(scratch_buff != NULL);
 
 	VERBOSE("Block %u - %u, page_start %u, nb %u, length %zu, offset %u\n",
 		block, end_block, page_start, nb_pages, length, offset);
@@ -41,7 +58,7 @@
 	*length_read = 0UL;
 
 	if (((start_offset != 0U) || (length % nand_dev.page_size) != 0U) &&
-	    (sizeof(scratch_buff) < nand_dev.page_size)) {
+	    (scratch_buff_size < nand_dev.page_size)) {
 		return -EINVAL;
 	}
 
diff --git a/include/drivers/nand.h b/include/drivers/nand.h
index 1b78ad4..5e5607c 100644
--- a/include/drivers/nand.h
+++ b/include/drivers/nand.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2019-2021, STMicroelectronics - All Rights Reserved
+ * Copyright (c) 2019-2022, STMicroelectronics - All Rights Reserved
  *
  * SPDX-License-Identifier: BSD-3-Clause
  */
@@ -33,6 +33,8 @@
 			     uintptr_t buffer);
 };
 
+void plat_get_scratch_buffer(void **buffer_addr, size_t *buf_size);
+
 /*
  * Read bytes from NAND device
  *