drm/radeon/kms: hopefully fix pll issues for real (v3)

The problematic boards have a recommended reference divider
to be used when spread spectrum is enabled on the laptop panel.
Enable the use of the recommended reference divider along with
the new pll algo.

v2: testing options

v3: When using the fixed reference divider with LVDS, prefer
min m to max p and use fractional feedback dividers.

Fixes:
https://bugzilla.kernel.org/show_bug.cgi?id=28852
https://bugzilla.kernel.org/show_bug.cgi?id=24462
https://bugzilla.kernel.org/show_bug.cgi?id=26552
MacbookPro issues reported by Justin Mattock <justinmattock@gmail.com>
Signed-off-by: Alex Deucher <alexdeucher@gmail.com>
Cc: stable@kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/atombios_crtc.c

@@ -538,7 +538,6 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
 			pll->flags |= RADEON_PLL_PREFER_HIGH_FB_DIV;
 		else
 			pll->flags |= RADEON_PLL_PREFER_LOW_REF_DIV;
-
 	}
 
 	list_for_each_entry(encoder, &dev->mode_config.encoder_list, head) {
@@ -555,29 +554,28 @@ static u32 atombios_adjust_pll(struct drm_crtc *crtc,
 					dp_clock = dig_connector->dp_clock;
 				}
 			}
-/* this might work properly with the new pll algo */
-#if 0 /* doesn't work properly on some laptops */
+
 			/* use recommended ref_div for ss */
 			if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT)) {
+				pll->flags |= RADEON_PLL_PREFER_MINM_OVER_MAXP;
 				if (ss_enabled) {
 					if (ss->refdiv) {
 						pll->flags |= RADEON_PLL_USE_REF_DIV;
 						pll->reference_div = ss->refdiv;
+						if (ASIC_IS_AVIVO(rdev))
+							pll->flags |= RADEON_PLL_USE_FRAC_FB_DIV;
 					}
 				}
 			}
-#endif
+
 			if (ASIC_IS_AVIVO(rdev)) {
 				/* DVO wants 2x pixel clock if the DVO chip is in 12 bit mode */
 				if (radeon_encoder->encoder_id == ENCODER_OBJECT_ID_INTERNAL_KLDSCP_DVO1)
 					adjusted_clock = mode->clock * 2;
 				if (radeon_encoder->active_device & (ATOM_DEVICE_TV_SUPPORT))
 					pll->flags |= RADEON_PLL_PREFER_CLOSEST_LOWER;
-				/* rv515 needs more testing with this option */
-				if (rdev->family != CHIP_RV515) {
 				if (radeon_encoder->devices & (ATOM_DEVICE_LCD_SUPPORT))
 					pll->flags |= RADEON_PLL_IS_LCD;
-				}
 			} else {
 				if (encoder->encoder_type != DRM_MODE_ENCODER_DAC)
 					pll->flags |= RADEON_PLL_NO_ODD_POST_DIV;
@@ -957,11 +955,7 @@ static void atombios_crtc_set_pll(struct drm_crtc *crtc, struct drm_display_mode
 	/* adjust pixel clock as needed */
 	adjusted_clock = atombios_adjust_pll(crtc, mode, pll, ss_enabled, &ss);
 
-	/* rv515 seems happier with the old algo */
-	if (rdev->family == CHIP_RV515)
-		radeon_compute_pll_legacy(pll, adjusted_clock, &pll_clock, &fb_div, &frac_fb_div,
-					  &ref_div, &post_div);
-	else if (ASIC_IS_AVIVO(rdev))
+	if (ASIC_IS_AVIVO(rdev))
 		radeon_compute_pll_avivo(pll, adjusted_clock, &pll_clock, &fb_div, &frac_fb_div,
 					 &ref_div, &post_div);
 	else