static bool
mxms_checksum(struct drm_device *dev)
{
	u16 size = mxms_headerlen(dev) + mxms_structlen(dev);
	u8 *mxms = mxms_data(dev), sum = 0;
	while (size--)
		sum += *mxms++;
	if (sum) {
		MXM_DBG(dev, "checksum invalid\n");
		return false;
	}
	return true;
}
static bool
mxms_foreach(struct drm_device *dev, u8 types,
	     bool (*exec)(struct drm_device *, u8 *, void *), void *info)
{
	u8 *mxms = mxms_data(dev);
	u8 *desc = mxms + mxms_headerlen(dev);
	u8 *fini = desc + mxms_structlen(dev) - 1;
	while (desc < fini) {
		u8 type = desc[0] & 0x0f;
		u8 headerlen = 0;
		u8 recordlen = 0;
		u8 entries = 0;

		switch (type) {
		case 0: 
			if (mxms_version(dev) >= 0x0300)
				headerlen = 8;
			else
				headerlen = 6;
			break;
		case 1: 
		case 2: 
		case 3: 
			headerlen = 4;
			break;
		case 4: 
			headerlen = 4;
			recordlen = 2;
			entries   = (ROM32(desc[0]) & 0x01f00000) >> 20;
			break;
		case 5: 
			headerlen = 8;
			break;
		case 6: 
			if (mxms_version(dev) >= 0x0300) {
				headerlen = 4;
				recordlen = 8;
				entries   = (desc[1] & 0xf0) >> 4;
			} else {
				headerlen = 8;
			}
			break;
		case 7: 
			headerlen = 8;
			recordlen = 4;
			entries   = desc[1] & 0x07;
			break;
		default:
			MXM_DBG(dev, "unknown descriptor type %d\n", type);
			return false;
		}
static bool
mxms_foreach(struct drm_device *dev, u8 types,
	     bool (*exec)(struct drm_device *, u8 *, void *), void *info)
{
	u8 *mxms = mxms_data(dev);
	u8 *desc = mxms + mxms_headerlen(dev);
	u8 *fini = desc + mxms_structlen(dev) - 1;
	while (desc < fini) {
		u8 type = desc[0] & 0x0f;
		u8 headerlen = 0;
		u8 recordlen = 0;
		u8 entries = 0;

		switch (type) {
		case 0: /* Output Device Structure */
			if (mxms_version(dev) >= 0x0300)
				headerlen = 8;
			else
				headerlen = 6;
			break;
		case 1: /* System Cooling Capability Structure */
		case 2: /* Thermal Structure */
		case 3: /* Input Power Structure */
			headerlen = 4;
			break;
		case 4: /* GPIO Device Structure */
			headerlen = 4;
			recordlen = 2;
			entries   = (ROM32(desc[0]) & 0x01f00000) >> 20;
			break;
		case 5: /* Vendor Specific Structure */
			headerlen = 8;
			break;
		case 6: /* Backlight Control Structure */
			if (mxms_version(dev) >= 0x0300) {
				headerlen = 4;
				recordlen = 8;
				entries   = (desc[1] & 0xf0) >> 4;
			} else {
				headerlen = 8;
			}
			break;
		case 7: /* Fan Control Structure */
			headerlen = 8;
			recordlen = 4;
			entries   = desc[1] & 0x07;
			break;
		default:
			MXM_DBG(dev, "unknown descriptor type %d\n", type);
			return false;
		}
static bool
mxms_valid(struct drm_device *dev)
{
	u8 *mxms = mxms_data(dev);
	if (*(u32 *)mxms != 0x5f4d584d) {
		MXM_DBG(dev, "signature invalid\n");
		return false;
	}

	if (!mxms_version(dev) || !mxms_checksum(dev))
		return false;

	return true;
}
static u16
mxms_version(struct drm_device *dev)
{
	u8 *mxms = mxms_data(dev);
	u16 version = (mxms[4] << 8) | mxms[5];
	switch (version ) {
	case 0x0200:
	case 0x0201:
	case 0x0300:
		return version;
	default:
		break;
	}

	MXM_DBG(dev, "unknown version %d.%d\n", mxms[4], mxms[5]);
	return 0x0000;
}