drm/amdgpu/gmc11: implement get_vbios_fb_size()

Implement get_vbios_fb_size() so we can properly reserve
the vbios splash screen to avoid potential artifacts on the
screen during the transition from the pre-OS console to the
OS console.
Acked-by: Sunil Khatri <sunil.khatri@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/gmc_v11_0.c

@@ -31,6 +31,8 @@
 #include "umc_v8_10.h"
 #include "athub/athub_3_0_0_sh_mask.h"
 #include "athub/athub_3_0_0_offset.h"
+#include "dcn/dcn_3_2_0_offset.h"
+#include "dcn/dcn_3_2_0_sh_mask.h"
 #include "oss/osssys_6_0_0_offset.h"
 #include "ivsrcid/vmc/irqsrcs_vmc_1_0.h"
 #include "navi10_enum.h"
@@ -546,7 +548,24 @@ static void gmc_v11_0_get_vm_pte(struct amdgpu_device *adev,
 
 static unsigned gmc_v11_0_get_vbios_fb_size(struct amdgpu_device *adev)
 {
-	return 0;
+	u32 d1vga_control = RREG32_SOC15(DCE, 0, regD1VGA_CONTROL);
+	unsigned size;
+
+	if (REG_GET_FIELD(d1vga_control, D1VGA_CONTROL, D1VGA_MODE_ENABLE)) {
+		size = AMDGPU_VBIOS_VGA_ALLOCATION;
+	} else {
+		u32 viewport;
+		u32 pitch;
+
+		viewport = RREG32_SOC15(DCE, 0, regHUBP0_DCSURF_PRI_VIEWPORT_DIMENSION);
+		pitch = RREG32_SOC15(DCE, 0, regHUBPREQ0_DCSURF_SURFACE_PITCH);
+		size = (REG_GET_FIELD(viewport,
+					HUBP0_DCSURF_PRI_VIEWPORT_DIMENSION, PRI_VIEWPORT_HEIGHT) *
+				REG_GET_FIELD(pitch, HUBPREQ0_DCSURF_SURFACE_PITCH, PITCH) *
+				4);
+	}
+
+	return size;
 }
 
 static const struct amdgpu_gmc_funcs gmc_v11_0_gmc_funcs = {