RISC-V: Access CSRs using CSR numbers

We should prefer accessing CSRs using their CSR numbers because:
1. It compiles fine with older toolchains.
2. We can use latest CSR names in #define macro names of CSR numbers
   as-per RISC-V spec.
3. We can access newly added CSRs even if toolchain does not recognize
   newly addes CSRs by name.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

arch/riscv/kernel/entry.S

@@ -37,11 +37,11 @@
 	 * the kernel thread pointer.  If we came from the kernel, sscratch
 	 * will contain 0, and we should continue on the current TP.
 	 */
-	csrrw tp, sscratch, tp
+	csrrw tp, CSR_SSCRATCH, tp
 	bnez tp, _save_context
 
 _restore_kernel_tpsp:
-	csrr tp, sscratch
+	csrr tp, CSR_SSCRATCH
 	REG_S sp, TASK_TI_KERNEL_SP(tp)
 _save_context:
 	REG_S sp, TASK_TI_USER_SP(tp)
@@ -87,11 +87,11 @@ _save_context:
 	li t0, SR_SUM | SR_FS
 
 	REG_L s0, TASK_TI_USER_SP(tp)
-	csrrc s1, sstatus, t0
-	csrr s2, sepc
-	csrr s3, sbadaddr
-	csrr s4, scause
-	csrr s5, sscratch
+	csrrc s1, CSR_SSTATUS, t0
+	csrr s2, CSR_SEPC
+	csrr s3, CSR_STVAL
+	csrr s4, CSR_SCAUSE
+	csrr s5, CSR_SSCRATCH
 	REG_S s0, PT_SP(sp)
 	REG_S s1, PT_SSTATUS(sp)
 	REG_S s2, PT_SEPC(sp)
@@ -107,8 +107,8 @@ _save_context:
 	.macro RESTORE_ALL
 	REG_L a0, PT_SSTATUS(sp)
 	REG_L a2, PT_SEPC(sp)
-	csrw sstatus, a0
-	csrw sepc, a2
+	csrw CSR_SSTATUS, a0
+	csrw CSR_SEPC, a2
 
 	REG_L x1,  PT_RA(sp)
 	REG_L x3,  PT_GP(sp)
@@ -155,7 +155,7 @@ ENTRY(handle_exception)
 	 * Set sscratch register to 0, so that if a recursive exception
 	 * occurs, the exception vector knows it came from the kernel
 	 */
-	csrw sscratch, x0
+	csrw CSR_SSCRATCH, x0
 
 	/* Load the global pointer */
 .option push
@@ -248,7 +248,7 @@ resume_userspace:
 	 * Save TP into sscratch, so we can find the kernel data structures
 	 * again.
 	 */
-	csrw sscratch, tp
+	csrw CSR_SSCRATCH, tp
 
 restore_all:
 	RESTORE_ALL