drm/amdgpu: adjust default dispclk (v2)

Set the default to 600Mhz if it's not set in the bios,
and bump the default to 600Mhz if it's lower than that.

Port of radeon commit:
9368931d

v2: clean up the code a bit

bug:
https://bugs.freedesktop.org/show_bug.cgi?id=91896Signed-off-by: NAlex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/amdgpu_atombios.c

@@ -672,8 +672,12 @@ int amdgpu_atombios_get_clock_info(struct amdgpu_device *adev)
 		/* disp clock */
 		adev->clock.default_dispclk =
 			le32_to_cpu(firmware_info->info_21.ulDefaultDispEngineClkFreq);
-		if (adev->clock.default_dispclk == 0)
-			adev->clock.default_dispclk = 54000; /* 540 Mhz */
+		/* set a reasonable default for DP */
+		if (adev->clock.default_dispclk < 53900) {
+			DRM_INFO("Changing default dispclk from %dMhz to 600Mhz\n",
+				 adev->clock.default_dispclk / 100);
+			adev->clock.default_dispclk = 60000;
+		}
 		adev->clock.dp_extclk =
 			le16_to_cpu(firmware_info->info_21.usUniphyDPModeExtClkFreq);
 		adev->clock.current_dispclk = adev->clock.default_dispclk;