Unverified Commit 8f3a2b4a authored by Anup Patel's avatar Anup Patel Committed by Palmer Dabbelt
Browse files

RISC-V: Move DT mapping outof fixmap 



Currently, RISC-V reserves 1MB of fixmap memory for device tree. However,
it maps only single PMD (2MB) space for fixmap which leaves only < 1MB space
left for other kernel features such as early ioremap which requires fixmap
as well. The fixmap size can be increased by another 2MB but it brings
additional complexity and changes the virtual memory layout as well.
If we require some additional feature requiring fixmap again, it has to be
moved again.

Technically, DT doesn't need a fixmap as the memory occupied by the DT is
only used during boot. That's why, We map device tree in early page table
using two consecutive PGD mappings at lower addresses (< PAGE_OFFSET).
This frees lot of space in fixmap and also makes maximum supported
device tree size supported as PGDIR_SIZE. Thus, init memory section can be used
for the same purpose as well. This simplifies fixmap implementation.

Signed-off-by: default avatarAnup Patel <anup.patel@wdc.com>
Signed-off-by: default avatarAtish Patra <atish.patra@wdc.com>
Reviewed-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
Signed-off-by: default avatarPalmer Dabbelt <palmerdabbelt@google.com>
parent 8a3f30c4

arch/riscv/include/asm/fixmap.h

+0 −3
Original line number Diff line number Diff line
@@ -22,9 +22,6 @@ 
 */

enum fixed_addresses {

	FIX_HOLE,

#define FIX_FDT_SIZE	SZ_1M

	FIX_FDT_END,

	FIX_FDT = FIX_FDT_END + FIX_FDT_SIZE / PAGE_SIZE - 1,

	FIX_PTE,

	FIX_PMD,

	FIX_TEXT_POKE1,

arch/riscv/include/asm/pgtable.h

+1 −0
Original line number Diff line number Diff line
@@ -464,6 +464,7 @@ static inline void __kernel_map_pages(struct page *page, int numpages, int enabl 
#define kern_addr_valid(addr)   (1) /* FIXME */



extern void *dtb_early_va;

extern uintptr_t dtb_early_pa;

void setup_bootmem(void);

void paging_init(void);

arch/riscv/kernel/head.S

+0 −1
Original line number Diff line number Diff line
@@ -258,7 +258,6 @@ clear_bss_done: 
#endif

	/* Start the kernel */

	call soc_early_init

	call parse_dtb

	tail start_kernel



.Lsecondary_start:

arch/riscv/kernel/head.h

+0 −2
Original line number Diff line number Diff line
@@ -16,6 +16,4 @@ asmlinkage void __init setup_vm(uintptr_t dtb_pa); 
extern void *__cpu_up_stack_pointer[];

extern void *__cpu_up_task_pointer[];



void __init parse_dtb(void);



#endif /* __ASM_HEAD_H */

arch/riscv/kernel/setup.c

+7 −2
Original line number Diff line number Diff line
@@ -48,8 +48,9 @@ atomic_t hart_lottery __section(.sdata); 
unsigned long boot_cpu_hartid;

static DEFINE_PER_CPU(struct cpu, cpu_devices);



void __init parse_dtb(void)

static void __init parse_dtb(void)

{

	/* Early scan of device tree from init memory */

	if (early_init_dt_scan(dtb_early_va))

		return;
@@ -62,6 +63,7 @@ void __init parse_dtb(void) 


void __init setup_arch(char **cmdline_p)

{

	parse_dtb();

	init_mm.start_code = (unsigned long) _stext;

	init_mm.end_code   = (unsigned long) _etext;

	init_mm.end_data   = (unsigned long) _edata;
@@ -76,7 +78,10 @@ void __init setup_arch(char **cmdline_p) 
#if IS_ENABLED(CONFIG_BUILTIN_DTB)

	unflatten_and_copy_device_tree();

#else

	if (early_init_dt_verify(__va(dtb_early_pa)))

		unflatten_device_tree();

	else

		pr_err("No DTB found in kernel mappings\n");

#endif



#ifdef CONFIG_SWIOTLB

CRA Git | Maintained and supported by SUSTech CRA and CCSE