[PATCH 6/6] drm/amd/pm: Fix SI DPM issues with high pixel clock

[Timur Kristóf]

We define "high pixelclock" for SI as higher than necessary
for 4K 30Hz. For example, 4K 60Hz and 1080p 144Hz fall into
this category.

When a high pixel clock display is connected, always disable
memory clock switching to solve some flickering that can be
observed on Tahiti and Pitcairn on 4K 60Hz displays.

When two high pixel clock displays are connected to Oland,
additionally disable shader clock switching, which results in
a higher voltage, thereby addressing some visible flickering.

Ideally, these issues would be solved by introducing something
like dce_calcs, but we don't have that for old GPUs, so
ad-hoc fixes become necessary.

Fixes: 841686df9f7d ("drm/amdgpu: add SI DPM support (v4)")
Signed-off-by: Timur Kristóf <timur.kristof at gmail.com>
---
 drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c | 37 ++++++++++++++++++++++
 1 file changed, 37 insertions(+)

diff --git a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
index e9f034ade214..7bfe39a7d653 100644
--- a/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
+++ b/drivers/gpu/drm/amd/pm/legacy-dpm/si_dpm.c
@@ -3443,12 +3443,14 @@ static void si_apply_state_adjust_rules(struct amdgpu_device *adev,
 {
 	struct  si_ps *ps = si_get_ps(rps);
 	struct amdgpu_clock_and_voltage_limits *max_limits;
+	struct amdgpu_connector *conn;
 	bool disable_mclk_switching = false;
 	bool disable_sclk_switching = false;
 	u32 mclk, sclk;
 	u16 vddc, vddci, min_vce_voltage = 0;
 	u32 max_sclk_vddc, max_mclk_vddci, max_mclk_vddc;
 	u32 max_sclk = 0, max_mclk = 0;
+	u32 high_pixelclock_count = 0;
 	int i;
 
 	if (adev->asic_type == CHIP_HAINAN) {
@@ -3476,6 +3478,41 @@ static void si_apply_state_adjust_rules(struct amdgpu_device *adev,
 		}
 	}
 
+	/* We define "high pixelclock" for SI as higher than necessary for 4K 30Hz.
+	 * For example, 4K 60Hz and 1080p 144Hz fall into this category.
+	 * Find number of such displays connected.
+	 */
+	for (i = 0; i < adev->mode_info.num_crtc; i++) {
+		if (!(adev->pm.dpm.new_active_crtcs & (1 << i)) ||
+			!adev->mode_info.crtcs[i]->enabled)
+			continue;
+
+		conn = to_amdgpu_connector(adev->mode_info.crtcs[i]->connector);
+
+		if (conn->pixelclock_for_modeset > 297000)
+			high_pixelclock_count++;
+	}
+
+	/* These are some ad-hoc fixes to some issues observed with SI GPUs.
+	 * They are necessary because we don't have something like dce_calcs
+	 * for these GPUs.
+	 */
+	if (high_pixelclock_count) {
+		/* High pixelclock displays need higher memory bandwidth.
+		 * Disable memory clock switching in order to:
+		 * - Solve visible display flickering
+		 * - Avoid starving other clients of the memory controller
+		 */
+		disable_mclk_switching = true;
+
+		/* On Oland, we observe some flickering when two 4K 60Hz
+		 * displays are connected, possibly because voltage is too low.
+		 * Raise the voltage by requiring a higher SCLK.
+		 */
+		if (high_pixelclock_count > 1 && adev->asic_type == CHIP_OLAND)
+			disable_sclk_switching = true;
+	}
+
 	if (rps->vce_active) {
 		rps->evclk = adev->pm.dpm.vce_states[adev->pm.dpm.vce_level].evclk;
 		rps->ecclk = adev->pm.dpm.vce_states[adev->pm.dpm.vce_level].ecclk;
-- 
2.50.1