tegra124: Add function for obtaining DRAM size via MC regs

This adds a method for obtaining DRAM size from memory controller
registers. It is intended as an SoC-specific helper function that
can be used from very early ramstage code.

BUG=none
BRANCH=none
TEST=built and booted on Nyan
Signed-off-by: David Hendricks <dhendrix@chromium.org>

Change-Id: Ib8b30e464b1398b78c5ffd8eada88b60d25ebf2b
Reviewed-on: https://chromium-review.googlesource.com/184535
Reviewed-by: David Hendricks <dhendrix@chromium.org>
Tested-by: David Hendricks <dhendrix@chromium.org>
Commit-Queue: David Hendricks <dhendrix@chromium.org>

src/soc/nvidia/tegra124/mc.h

@@ -115,6 +115,9 @@ struct tegra_mc_regs {
 };
 
 enum {
+	MC_EMEM_CFG_SIZE_MB_SHIFT = 0,
+	MC_EMEM_CFG_SIZE_MB_MASK = 0x3fff,
+
 	MC_EMEM_ARB_MISC0_MC_EMC_SAME_FREQ_SHIFT = 27,
 	MC_EMEM_ARB_MISC0_MC_EMC_SAME_FREQ_MASK = 1 << 27,
 

src/soc/nvidia/tegra124/sdram.c

@@ -609,3 +609,24 @@ uint32_t sdram_get_ram_code(void)
 		 PMC_STRAPPING_OPT_A_RAM_CODE_MASK) >>
 		PMC_STRAPPING_OPT_A_RAM_CODE_SHIFT);
 }
+
+/* returns total amount of DRAM (in MB) from memory controller registers */
+int sdram_size_mb(void)
+{
+	struct tegra_mc_regs *mc = (struct tegra_mc_regs *)TEGRA_MC_BASE;
+	static int total_size = 0;
+
+	if (total_size)
+		return total_size;
+
+	/*
+	 * This obtains memory size from the External Memory Aperture
+	 * Configuration register. Nvidia confirmed that it is safe to assume
+	 * this value represents the total physical DRAM size.
+	 */
+	total_size = (read32(&mc->emem_cfg) >>
+			MC_EMEM_CFG_SIZE_MB_SHIFT) & MC_EMEM_CFG_SIZE_MB_MASK;
+
+	printk(BIOS_DEBUG, "%s: Total SDRAM (MB): %u\n", __func__, total_size);
+	return total_size;
+}

src/soc/nvidia/tegra124/sdram.h

@@ -24,5 +24,6 @@
 
 uint32_t sdram_get_ram_code(void);
 void sdram_init(const struct sdram_params *param);
+int sdram_size_mb(void);
 
 #endif /* __SOC_NVIDIA_TEGRA124_SDRAM_H__ */