DA850 EVM: passing maximum clock rate information to kernel

The TI DA850/OMAP-L138/AM18x EVM can be populated with devices
having different maximum allowed CPU clock rating.

The maximum clock the chip can support can only be determined from
the label on the package (not software readable).

Introduce a method to pass the maximum allowed clock rate information
to kernel using ATAG_REVISION. The kernel uses this information to
determine the maximum cpu clock rate reachable using cpufreq.

Note that U-Boot itself does not set the CPU clock rate. The CPU
clock is setup by a primary bootloader ("UBL"). The rate setup by
UBL could be different from the maximum clock rate supported by the
device.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Sandeep Paulraj <s-paulraj@ti.com>

board/davinci/da8xxevm/da850evm.c

@@ -118,6 +118,39 @@ static const struct lpsc_resource lpsc[] = {
 	{ DAVINCI_LPSC_GPIO },
 };
 
+#ifndef CONFIG_DA850_EVM_MAX_CPU_CLK
+#define CONFIG_DA850_EVM_MAX_CPU_CLK	300000000
+#endif
+
+/*
+ * get_board_rev() - setup to pass kernel board revision information
+ * Returns:
+ * bit[0-3]	Maximum cpu clock rate supported by onboard SoC
+ *		0000b - 300 MHz
+ *		0001b - 372 MHz
+ *		0010b - 408 MHz
+ *		0011b - 456 MHz
+ */
+u32 get_board_rev(void)
+{
+	char *s;
+	u32 maxcpuclk = CONFIG_DA850_EVM_MAX_CPU_CLK;
+	u32 rev = 0;
+
+	s = getenv("maxcpuclk");
+	if (s)
+		maxcpuclk = simple_strtoul(s, NULL, 10);
+
+	if (maxcpuclk >= 456000000)
+		rev = 3;
+	else if (maxcpuclk >= 408000000)
+		rev = 2;
+	else if (maxcpuclk >= 372000000)
+		rev = 1;
+
+	return rev;
+}
+
 int board_init(void)
 {
 #ifndef CONFIG_USE_IRQ

doc/README.davinci

@@ -95,6 +95,20 @@ into the RAM.
 The programmers and UBL are always released as part of any standard TI
 software release associated with an SOC.
 
+Environment Variables
+=====================
+
+The DA850 EVM allows the user to specify the maximum cpu clock allowed by the
+silicon, in Hz, via an environment variable "maxcpuclk".
+
+The maximum clock rate allowed depends on the silicon populated on the EVM.
+Please make sure you understand the restrictions placed on this clock in the
+device specific datasheet before setting up this variable. This information is
+passed to the Linux kernel using the ATAG_REVISION atag.
+
+If "maxcpuclk" is not defined, the configuration CONFIG_DA850_EVM_MAX_CPU_CLK
+is used to obtain this information.
+
 Links
 =====
 

include/configs/da850evm.h

@@ -140,6 +140,7 @@
  */
 #define LINUX_BOOT_PARAM_ADDR	(PHYS_SDRAM_1 + 0x100)
 #define CONFIG_CMDLINE_TAG
+#define CONFIG_REVISION_TAG
 #define CONFIG_SETUP_MEMORY_TAGS
 #define CONFIG_BOOTARGS		\
 	"mem=32M console=ttyS2,115200n8 root=/dev/mtdblock2 rw noinitrd ip=dhcp"