+struct memdev_dmi_entry {
+ u8 type;
+ u8 length;
+ u16 handle;
+ u16 phys_mem_array_handle;
+ u16 mem_err_info_handle;
+ u16 total_width;
+ u16 data_width;
+ u16 size;
+ u8 form;
+ u8 device_set;
+ u8 device_locator;
+ u8 bank_locator;
+ u8 memory_type;
+ u16 type_detail;
+ u16 speed;
+ u8 manufacturer;
+ u8 serial_number;
+ u8 asset_tag;
+ u8 part_number;
+ u8 attributes;
+ u32 extended_size;
+ u16 conf_mem_clk_speed;
+} __attribute__((__packed__));
+
+
+/*
+ * Decode the DRAM Clock Frequency, be paranoid, make sure that all
+ * memory devices show the same speed, and if they don't then consider
+ * all speeds to be invalid.
+ */
+static void decode_dclk(const struct dmi_header *dh, void *_dclk_freq)
+{
+ int *dclk_freq = _dclk_freq;
+ u16 dmi_mem_clk_speed;
+
+ if (*dclk_freq == -1)
+ return;
+
+ if (dh->type == DMI_ENTRY_MEM_DEVICE) {
+ struct memdev_dmi_entry *memdev_dmi_entry =
+ (struct memdev_dmi_entry *)dh;
+ unsigned long conf_mem_clk_speed_offset =
+ (unsigned long)&memdev_dmi_entry->conf_mem_clk_speed -
+ (unsigned long)&memdev_dmi_entry->type;
+ unsigned long speed_offset =
+ (unsigned long)&memdev_dmi_entry->speed -
+ (unsigned long)&memdev_dmi_entry->type;
+
+ /* Check that a DIMM is present */
+ if (memdev_dmi_entry->size == 0)
+ return;
+
+ /*
+ * Pick the configured speed if it's available, otherwise
+ * pick the DIMM speed, or we don't have a speed.
+ */
+ if (memdev_dmi_entry->length > conf_mem_clk_speed_offset) {
+ dmi_mem_clk_speed =
+ memdev_dmi_entry->conf_mem_clk_speed;
+ } else if (memdev_dmi_entry->length > speed_offset) {
+ dmi_mem_clk_speed = memdev_dmi_entry->speed;
+ } else {
+ *dclk_freq = -1;
+ return;
+ }
+
+ if (*dclk_freq == 0) {
+ /* First pass, speed was 0 */
+ if (dmi_mem_clk_speed > 0) {
+ /* Set speed if a valid speed is read */
+ *dclk_freq = dmi_mem_clk_speed;
+ } else {
+ /* Otherwise we don't have a valid speed */
+ *dclk_freq = -1;
+ }
+ } else if (*dclk_freq > 0 &&
+ *dclk_freq != dmi_mem_clk_speed) {
+ /*
+ * If we have a speed, check that all DIMMS are the same
+ * speed, otherwise set the speed as invalid.
+ */
+ *dclk_freq = -1;
+ }
+ }
+}
+
+/*
+ * The default DCLK frequency is used as a fallback if we
+ * fail to find anything reliable in the DMI. The value
+ * is taken straight from the datasheet.
+ */
+#define DEFAULT_DCLK_FREQ 800
+
+static int get_dclk_freq(void)
+{
+ int dclk_freq = 0;
+
+ dmi_walk(decode_dclk, (void *)&dclk_freq);
+
+ if (dclk_freq < 1)
+ return DEFAULT_DCLK_FREQ;
+
+ return dclk_freq;
+}
+