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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: Anup Patel <anup.patel@wdc.com> Signed-off-by: Atish Patra <atish.patra@wdc.com> Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>
47 lines
1.1 KiB
C
47 lines
1.1 KiB
C
/* SPDX-License-Identifier: GPL-2.0 */
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/*
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* Copyright (C) 2019 Western Digital Corporation or its affiliates.
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*/
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#ifndef _ASM_RISCV_FIXMAP_H
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#define _ASM_RISCV_FIXMAP_H
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#include <linux/kernel.h>
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#include <linux/sizes.h>
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#include <linux/pgtable.h>
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#include <asm/page.h>
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#ifdef CONFIG_MMU
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/*
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* Here we define all the compile-time 'special' virtual addresses.
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* The point is to have a constant address at compile time, but to
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* set the physical address only in the boot process.
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*
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* These 'compile-time allocated' memory buffers are page-sized. Use
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* set_fixmap(idx,phys) to associate physical memory with fixmap indices.
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*/
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enum fixed_addresses {
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FIX_HOLE,
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FIX_PTE,
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FIX_PMD,
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FIX_TEXT_POKE1,
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FIX_TEXT_POKE0,
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FIX_EARLYCON_MEM_BASE,
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__end_of_fixed_addresses
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};
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#define FIXMAP_PAGE_IO PAGE_KERNEL
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#define __early_set_fixmap __set_fixmap
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#define __late_set_fixmap __set_fixmap
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#define __late_clear_fixmap(idx) __set_fixmap((idx), 0, FIXMAP_PAGE_CLEAR)
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extern void __set_fixmap(enum fixed_addresses idx,
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phys_addr_t phys, pgprot_t prot);
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#include <asm-generic/fixmap.h>
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#endif /* CONFIG_MMU */
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#endif /* _ASM_RISCV_FIXMAP_H */
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