[RFC PATCH V2 21/38] riscv: s64ilp32: Add MMU_SV32 mode support

[guoren]

From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>

This needs to add Sv32 mode in the SATP CSR of RV64 ISA, a novel
extension of 64-bit processors' MMU. It could save a bit of page
table footprint and improve the page table walk performance:

s64ilp32 with Sv39:
PageTables:          136 kB

s64ilp32 with Sv32:
PageTables:           60 kB

Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx>
Signed-off-by: Guo Ren <guoren@xxxxxxxxxx>
---
 arch/riscv/Kconfig           | 11 ++++++++++-
 arch/riscv/Kconfig.errata    |  2 +-
 arch/riscv/include/asm/csr.h |  1 +
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
index 5a3eb5e7d67a..1d3a236d2c45 100644
--- a/arch/riscv/Kconfig
+++ b/arch/riscv/Kconfig
@@ -481,7 +481,7 @@ config RISCV_ISA_SVNAPOT
 
 config RISCV_ISA_SVPBMT
 	bool "Svpbmt extension support for supervisor mode page-based memory types"
-	depends on 64BIT && MMU
+	depends on !MMU_SV32 && MMU
 	depends on RISCV_ALTERNATIVE
 	default y
 	help
@@ -638,6 +638,15 @@ config THREAD_SIZE_ORDER
 	  Specify the Pages of thread stack size (from 4KB to 64KB), which also
 	  affects irq stack size, which is equal to thread stack size.
 
+config MMU_SV32
+	bool "MMU Sv32"
+	depends on 32BIT && MMU
+	help
+	  ARCH_RV32I only supports MMU Sv32 mode, but ARCH_RV64ILP32 supports
+	  MMU Sv39 & Sv32 (MMU Sv32 is optional for RV64 hardware).
+
+	  If unsure, say N.
+
 endmenu # "Platform type"
 
 menu "Kernel features"
diff --git a/arch/riscv/Kconfig.errata b/arch/riscv/Kconfig.errata
index 0c8f4652cd82..1aa85a427ff3 100644
--- a/arch/riscv/Kconfig.errata
+++ b/arch/riscv/Kconfig.errata
@@ -44,7 +44,7 @@ config ERRATA_THEAD
 
 config ERRATA_THEAD_PBMT
 	bool "Apply T-Head memory type errata"
-	depends on ERRATA_THEAD && 64BIT && MMU
+	depends on ERRATA_THEAD && !MMU_SV32 && MMU
 	select RISCV_ALTERNATIVE_EARLY
 	default y
 	help
diff --git a/arch/riscv/include/asm/csr.h b/arch/riscv/include/asm/csr.h
index 03acdedc100d..aa78c5f20d75 100644
--- a/arch/riscv/include/asm/csr.h
+++ b/arch/riscv/include/asm/csr.h
@@ -65,6 +65,7 @@
 #define SATP_ASID_MASK	_AC(0x1FF, UXL)
 #else
 #define SATP_PPN	_AC(0x00000FFFFFFFFFFF, UXL)
+#define SATP_MODE_32	_AC(0x1000000000000000, UXL)
 #define SATP_MODE_39	_AC(0x8000000000000000, UXL)
 #define SATP_MODE_48	_AC(0x9000000000000000, UXL)
 #define SATP_MODE_57	_AC(0xa000000000000000, UXL)
-- 
2.36.1