imx: Add a common way for detecting NXP boards revision

NXP development boards based on i.MX6/i.MX7 contain the board
revision information stored in the fuses.

Introduce a common function that can be shared by different boards and
convert mx6sabreauto to use this new mechanism.

Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>

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

@@ -109,6 +109,9 @@ void imx_wdog_disable_powerdown(void);
 
 int board_mmc_get_env_dev(int devno);
 
+int nxp_board_rev(void);
+char nxp_board_rev_string(void);
+
 /*
  * Initializes on-chip ethernet controllers.
  * to override, implement board_eth_init()

arch/arm/mach-imx/Kconfig

@@ -61,3 +61,11 @@ config CMD_HDMIDETECT
 	help
 	  This enables the 'hdmidet' command which detects if an HDMI monitor
 	  is connected.
+
+config NXP_BOARD_REVISION
+	bool "Read NXP board revision from fuses"
+	depends on ARCH_MX6 || ARCH_MX7
+	help
+	  NXP boards based on i.MX6/7 contain the board revision information
+	  stored in the fuses. Select this option if you want to be able to
+	  retrieve the board revision information.

arch/arm/mach-imx/cpu.c

@@ -323,3 +323,28 @@ void set_chipselect_size(int const cs_size)
 
 	writel(reg, &iomuxc_regs->gpr[1]);
 }
+
+#ifdef CONFIG_NXP_BOARD_REVISION
+int nxp_board_rev(void)
+{
+	/*
+	 * Get Board ID information from OCOTP_GP1[15:8]
+	 * RevA: 0x1
+	 * RevB: 0x2
+	 * RevC: 0x3
+	 */
+	struct ocotp_regs *ocotp = (struct ocotp_regs *)OCOTP_BASE_ADDR;
+	struct fuse_bank *bank = &ocotp->bank[4];
+	struct fuse_bank4_regs *fuse =
+			(struct fuse_bank4_regs *)bank->fuse_regs;
+
+	return (readl(&fuse->gp1) >> 8 & 0x0F);
+}
+
+char nxp_board_rev_string(void)
+{
+	const char *rev = "A";
+
+	return (*rev + nxp_board_rev() - 1);
+}
+#endif