imx8: add rom api wrappers

The ROM API is thoroughly undocumented, but apparently passing the xor
of the real arguments as an extra argument is required [1]. Also, we
need to do the "save gd/restore gd" dance. These are both error-prone,
and lead to a lot of code duplication.

Since both imx8m[np] and imx8ulp SOCs have this, add a separate
translation unit which is included precisely when the new
CONFIG_IMX8_ROMAPI symbol is set, which provide convenience wrappers
that take care of computing the xor value as well as doing the gd
dance, and that thus have a more intuitive API. Subsequent patches
will make use of these to reduce boilerplate.

[1] One wonders, for example, if the check is only applied to the
lower 32 bits, or if we're implicitly relying on all 64-bit pointer
values we're passing effectively have 0 in the upper 32 bits.

Reviewed-by: Peng Fan <peng.fan@nxp.com>
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>

arch/arm/include/asm/mach-imx/sys_proto.h

@@ -178,6 +178,10 @@ enum boot_dev_type_e {
 #define ROM_API_OKAY		0xF0
 
 extern struct rom_api *g_rom_api;
+
+u32 rom_api_download_image(u8 *dest, u32 offset, u32 size);
+u32 rom_api_query_boot_infor(u32 info_type, u32 *info);
+
 #endif
 
 /* For i.MX ULP */

arch/arm/mach-imx/Makefile

@@ -243,3 +243,4 @@ obj-$(CONFIG_ARCH_IMX8) += imx8/
 obj-$(CONFIG_ARCH_IMXRT) += imxrt/
 
 obj-$(CONFIG_SPL_BOOTROM_SUPPORT) += spl_imx_romapi.o
+obj-$(CONFIG_IMX8_ROMAPI) += romapi.o

arch/arm/mach-imx/romapi.c

@@ -0,0 +1,30 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+#include <asm/global_data.h>
+#include <asm/arch/sys_proto.h>
+
+DECLARE_GLOBAL_DATA_PTR;
+
+u32 rom_api_download_image(u8 *dest, u32 offset, u32 size)
+{
+	u32 xor = (uintptr_t)dest ^ offset ^ size;
+	volatile gd_t *sgd = gd;
+	u32 ret;
+
+	ret = g_rom_api->download_image(dest, offset, size, xor);
+	set_gd(sgd);
+
+	return ret;
+}
+
+u32 rom_api_query_boot_infor(u32 info_type, u32 *info)
+{
+	u32 xor = info_type ^ (uintptr_t)info;
+	volatile gd_t *sgd = gd;
+	u32 ret;
+
+	ret = g_rom_api->query_boot_infor(info_type, info, xor);
+	set_gd(sgd);
+
+	return ret;
+}