drm/mgag200: Added resolution and bandwidth limits for various G200e products.

At the larger resolutions, the g200e series sometimes struggles with
maintaining a proper output. Problems like flickering or black bands appearing
on screen can occur. In order to avoid this, limitations regarding resolutions
and bandwidth have been added for the different variations of the g200e series.
This code was ported from the old xorg mga driver.

Signed-off-by: Julia Lemire <[e-mail]>
Cc: [e-mail]
Signed-off-by: Dave Airlie <[e-mail]>

drivers/gpu/drm/mgag200/mgag200_drv.h

···
 		struct ttm_bo_device bdev;
 	} ttm;
 
-	u32 reg_1e24; /* SE model number */
+	/* SE model number stored in reg 0x1e24 */
+	u32 unique_rev_id;
 };
 
 

drivers/gpu/drm/mgag200/mgag200_main.c

···
 
 	/* stash G200 SE model number for later use */
 	if (IS_G200_SE(mdev))
-		mdev->reg_1e24 = RREG32(0x1e24);
+		mdev->unique_rev_id = RREG32(0x1e24);
 
 	ret = mga_vram_init(mdev);
 	if (ret)

drivers/gpu/drm/mgag200/mgag200_mode.c

···
 
 
 	if (IS_G200_SE(mdev)) {
-		if (mdev->reg_1e24 >= 0x02) {
+		if (mdev->unique_rev_id >= 0x02) {
 			u8 hi_pri_lvl;
 			u32 bpp;
 			u32 mb;
···
 			WREG8(MGAREG_CRTCEXT_DATA, hi_pri_lvl);
 		} else {
 			WREG8(MGAREG_CRTCEXT_INDEX, 0x06);
-			if (mdev->reg_1e24 >= 0x01)
+			if (mdev->unique_rev_id >= 0x01)
 				WREG8(MGAREG_CRTCEXT_DATA, 0x03);
 			else
 				WREG8(MGAREG_CRTCEXT_DATA, 0x04);
···
 	return ret;
 }
 
+static uint32_t mga_vga_calculate_mode_bandwidth(struct drm_display_mode *mode,
+							int bits_per_pixel)
+{
+	uint32_t total_area, divisor;
+	int64_t active_area, pixels_per_second, bandwidth;
+	uint64_t bytes_per_pixel = (bits_per_pixel + 7) / 8;
+
+	divisor = 1024;
+
+	if (!mode->htotal || !mode->vtotal || !mode->clock)
+		return 0;
+
+	active_area = mode->hdisplay * mode->vdisplay;
+	total_area = mode->htotal * mode->vtotal;
+
+	pixels_per_second = active_area * mode->clock * 1000;
+	do_div(pixels_per_second, total_area);
+
+	bandwidth = pixels_per_second * bytes_per_pixel * 100;
+	do_div(bandwidth, divisor);
+
+	return (uint32_t)(bandwidth);
+}
+
+#define MODE_BANDWIDTH	MODE_BAD
+
 static int mga_vga_mode_valid(struct drm_connector *connector,
 				 struct drm_display_mode *mode)
 {
···
 	int bpp = 32;
 	int i = 0;
 
-	/* FIXME: Add bandwidth and g200se limitations */
+	if (IS_G200_SE(mdev)) {
+		if (mdev->unique_rev_id == 0x01) {
+			if (mode->hdisplay > 1600)
+				return MODE_VIRTUAL_X;
+			if (mode->vdisplay > 1200)
+				return MODE_VIRTUAL_Y;
+			if (mga_vga_calculate_mode_bandwidth(mode, bpp)
+				> (24400 * 1024))
+				return MODE_BANDWIDTH;
+		} else if (mdev->unique_rev_id >= 0x02) {
+			if (mode->hdisplay > 1920)
+				return MODE_VIRTUAL_X;
+			if (mode->vdisplay > 1200)
+				return MODE_VIRTUAL_Y;
+			if (mga_vga_calculate_mode_bandwidth(mode, bpp)
+				> (30100 * 1024))
+				return MODE_BANDWIDTH;
+		}
+	} else if (mdev->type == G200_WB) {
+		if (mode->hdisplay > 1280)
+			return MODE_VIRTUAL_X;
+		if (mode->vdisplay > 1024)
+			return MODE_VIRTUAL_Y;
+		if (mga_vga_calculate_mode_bandwidth(mode,
+			bpp > (31877 * 1024)))
+			return MODE_BANDWIDTH;
+	} else if (mdev->type == G200_EV &&
+		(mga_vga_calculate_mode_bandwidth(mode, bpp)
+			> (32700 * 1024))) {
+		return MODE_BANDWIDTH;
+	} else if (mode->type == G200_EH &&
+		(mga_vga_calculate_mode_bandwidth(mode, bpp)
+			> (37500 * 1024))) {
+		return MODE_BANDWIDTH;
+	} else if (mode->type == G200_ER &&
+		(mga_vga_calculate_mode_bandwidth(mode,
+			bpp) > (55000 * 1024))) {
+		return MODE_BANDWIDTH;
+	}
 
 	if (mode->crtc_hdisplay > 2048 || mode->crtc_hsync_start > 4096 ||
 	    mode->crtc_hsync_end > 4096 || mode->crtc_htotal > 4096 ||