[PATCH 2/3] ARM: i.MX8M: return error if imx_load_image can't honour entry address

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On i.MX6 and 7, we call imx_load_image with start == true and address
equal to entry.

On i.MX8M, we call imx_load_image with start == false and address
unequal to entry.

imx_load_image interprets the address being unequal to entry as a
directive to move the image, so that the barebox entry point without
the i.MX header starts at exactly the entry address.

If we were to change this, say on an i.MX8MN, so address is equal
to entry, the system will no longer boot:

  - i.MX header is loaded to offset 0 from start of SDRAM (like on i.MX6/7)
  - barebox PBL entry point is loaded to offset 32K
  - imx8mX_load_bl33 will copy the running barebox PBL to offset 0

The result of this is that the TF-A will be able to return to barebox
(non-executable i.MX header overwritten with executable PBL), but
uncompressing barebox will fail (remainder of partially overwritten
PBL is interpreted as start of piggydata).

Add some documentation explaining this complexity, a hint on how we
could improve it and change the condition, so entry == address results
in an explicit warning message immediately.

Reported-by: Marco Felsch <m.felsch@pengutronix.de>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
---
 arch/arm/mach-imx/xload-common.c | 32 +++++++++++++++++++++++++++++++-
 1 file changed, 31 insertions(+), 1 deletion(-)

diff --git a/arch/arm/mach-imx/xload-common.c b/arch/arm/mach-imx/xload-common.c
index 03eb2ef109e3..32f12cd7f574 100644
--- a/arch/arm/mach-imx/xload-common.c
+++ b/arch/arm/mach-imx/xload-common.c
@@ -78,6 +78,25 @@ imx_search_header(struct imx_flash_header_v2 **header_pointer,
 	return 0;
 }
 
+/**
+ * imx_load_image - Load i.MX barebox image from boot medium
+ * @address: Start address of SDRAM where barebox can be loaded into
+ * @entry: Address where barebox entry point should be placed.
+ *         This is ignored unless @start == false
+ * @offset: Start offset for i.MX header search
+ * @ivt_offset: offset between i.MX header and IVT
+ * @start: whether image should be started after loading
+ * @alignment: If nonzero, image size hardcoded in PBL will be aligned up
+ *             to this value
+ * @read: function pointer for reading from the beginning of the boot
+ *        medium onwards
+ * @priv: private data pointer passed to read function
+ *
+ * Return: A negative error code on failure.
+ * On success, if @start == true, the function will not return.
+ * If @start == false, the function will return 0 after placing the
+ * barebox entry point (without header) at @entry.
+ */
 int imx_load_image(ptrdiff_t address, ptrdiff_t entry, u32 offset,
 		   u32 ivt_offset, bool start, unsigned int alignment,
 		   int (*read)(void *dest, size_t len, void *priv),
@@ -102,7 +121,7 @@ int imx_load_image(ptrdiff_t address, ptrdiff_t entry, u32 offset,
 
 	ofs = offset + hdr->entry - hdr->boot_data.start;
 
-	if (entry != address) {
+	if (!start) {
 		/*
 		 * Passing entry different from address is interpreted
 		 * as a request to place the image such that its entry
@@ -129,6 +148,17 @@ int imx_load_image(ptrdiff_t address, ptrdiff_t entry, u32 offset,
 		buf = (void *)(entry - ofs);
 	}
 
+	/*
+	 * For SD/MMC High-Capacity support (> 2G), the offset for the block
+	 * read command is in blocks, not bytes. We don't have the information
+	 * whether we have a SDHC card or not, when we run here though, because
+	 * card setup was done by BootROM. To workaround this, we just read
+	 * from offset 0 as 0 blocks == 0 bytes.
+	 *
+	 * A result of this is that we will have to read the i.MX header and
+	 * padding in front of the binary first to arrive at the barebox entry
+	 * point.
+	 */
 	ret = read(buf, ofs + len, priv);
 	if (ret) {
 		pr_err("Loading image failed with %d\n", ret);
-- 
2.39.2