drm/asahi: Move the unknown dummy page to the top of the address space

Signed-off-by: Asahi Lina <lina@asahilina.net>

Author: hoshinolina

drivers/gpu/drm/asahi/file.rs

@@ -170,8 +170,6 @@ const VM_DRV_GPU_END: u64 = 0x70_ffffffff;
 const VM_DRV_GPUFW_START: u64 = 0x71_00000000;
 /// End address of the kernel-managed GPU/FW shared mapping region.
 const VM_DRV_GPUFW_END: u64 = 0x71_ffffffff;
-/// Address of a special dummy page?
-const VM_UNK_PAGE: u64 = 0x6f_ffff8000;
 
 impl drm::file::DriverFile for File {
     type Driver = driver::AsahiDriver;
@@ -349,7 +347,8 @@ impl File {
         );
         let mut dummy_obj = gem::new_kernel_object(device, 0x4000)?;
         dummy_obj.vmap()?.as_mut_slice().fill(0);
-        let dummy_mapping = dummy_obj.map_at(&vm, VM_UNK_PAGE, mmu::PROT_GPU_SHARED_RW, true)?;
+        let dummy_mapping =
+            dummy_obj.map_at(&vm, mmu::IOVA_UNK_PAGE, mmu::PROT_GPU_SHARED_RW, true)?;
 
         mod_dev_dbg!(device, "[File {} VM {}]: VM created\n", file_id, id);
         resv.store(Box::new(Vm {

drivers/gpu/drm/asahi/initdata.rs

@@ -487,10 +487,12 @@ impl<'a> InitDataBuilder::ver<'a> {
                 #[ver(V < V13_0B4)]
                 unk_10: U64(0x1_00000000),
                 unk_18: U64(0xffc00000),
-                unk_20: U64(0x11_00000000),
-                unk_28: U64(0x11_00000000),
-                // userspace address?
-                unk_30: U64(0x6f_ffff8000),
+                // USC start
+                unk_20: U64(0), // U64(0x11_00000000),
+                unk_28: U64(0), // U64(0x11_00000000),
+                // Unknown page
+                //unk_30: U64(0x6f_ffff8000),
+                unk_30: U64(mmu::IOVA_UNK_PAGE),
                 // unmapped?
                 unkptr_38: U64(0xffffffa0_11800000),
                 // TODO: yuv matrices

drivers/gpu/drm/asahi/mmu.rs

@@ -87,6 +87,10 @@ const TTBR_ASID_SHIFT: usize = 48;
 
 const PTE_TABLE: u64 = 0x3; // BIT(0) | BIT(1)
 
+/// Address of a special dummy page?
+//const IOVA_UNK_PAGE: u64 = 0x6f_ffff8000;
+pub(crate) const IOVA_UNK_PAGE: u64 = IOVA_USER_TOP - 2 * UAT_PGSZ as u64;
+
 // KernelMapping protection types
 
 // Note: prot::CACHE means "cache coherency", which for UAT means *uncached*,