RISC-V: always select RISCV_ALTERNATIVE for non-xip kernels

When moving switch_to's has_fpu() over to using
riscv_has_extension_likely() rather than static branches, the FPU code
gained a dependency on the alternatives framework.
That dependency has now been removed, as riscv_has_extension_ikely() now
contains a fallback path, using __riscv_isa_extension_available(), but
if CONFIG_RISCV_ALTERNATIVE isn't selected when CONFIG_FPU is, has_fpu()
checks will not benefit from the "fast path" that the alternatives
framework provides.

We want to ensure that alternatives are available whenever
riscv_has_extension_[un]likely() is used, rather than silently falling
back to the slow path, but rather than rely on selecting
RISCV_ALTERNATIVE in the myriad of locations that may use
riscv_has_extension_[un]likely(), select it (almost) always instead by
adding it to the main RISCV config entry.
xip kernels cannot make use of the alternatives framework, so it is not
enabled for those configurations, although this is the status quo.

All current sites that select RISCV_ALTERNATIVE are converted to
dependencies on the option instead. The explicit dependencies on
!XIP_KERNEL can be dropped, as RISCV_ALTERNATIVE is not user selectable.

Fixes: 702e645 ("riscv: fpu: switch has_fpu() to riscv_has_extension_likely()")
Link: https://lore.kernel.org/all/[email protected]/
Reported-by: Jason A. Donenfeld <[email protected]>
Signed-off-by: Conor Dooley <[email protected]>
Reviewed-by: Andrew Jones <[email protected]>
Reviewed-by: Jason A. Donenfeld <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Palmer Dabbelt <[email protected]>

Author: ConchuOD

arch/riscv/Kconfig

@@ -126,6 +126,7 @@ config RISCV
 	select OF_IRQ
 	select PCI_DOMAINS_GENERIC if PCI
 	select PCI_MSI if PCI
+	select RISCV_ALTERNATIVE if !XIP_KERNEL
 	select RISCV_INTC
 	select RISCV_TIMER if RISCV_SBI
 	select SIFIVE_PLIC
@@ -401,9 +402,8 @@ config RISCV_ISA_C
 config RISCV_ISA_SVPBMT
 	bool "SVPBMT extension support"
 	depends on 64BIT && MMU
-	depends on !XIP_KERNEL
+	depends on RISCV_ALTERNATIVE
 	default y
-	select RISCV_ALTERNATIVE
 	help
 	   Adds support to dynamically detect the presence of the SVPBMT
 	   ISA-extension (Supervisor-mode: page-based memory types) and
@@ -428,8 +428,8 @@ config TOOLCHAIN_HAS_ZBB
 config RISCV_ISA_ZBB
 	bool "Zbb extension support for bit manipulation instructions"
 	depends on TOOLCHAIN_HAS_ZBB
-	depends on !XIP_KERNEL && MMU
-	select RISCV_ALTERNATIVE
+	depends on MMU
+	depends on RISCV_ALTERNATIVE
 	default y
 	help
 	   Adds support to dynamically detect the presence of the ZBB
@@ -443,9 +443,9 @@ config RISCV_ISA_ZBB
 
 config RISCV_ISA_ZICBOM
 	bool "Zicbom extension support for non-coherent DMA operation"
-	depends on !XIP_KERNEL && MMU
+	depends on MMU
+	depends on RISCV_ALTERNATIVE
 	default y
-	select RISCV_ALTERNATIVE
 	select RISCV_DMA_NONCOHERENT
 	help
 	   Adds support to dynamically detect the presence of the ZICBOM

arch/riscv/Kconfig.erratas

@@ -2,8 +2,7 @@ menu "CPU errata selection"
 
 config ERRATA_SIFIVE
 	bool "SiFive errata"
-	depends on !XIP_KERNEL
-	select RISCV_ALTERNATIVE
+	depends on RISCV_ALTERNATIVE
 	help
 	  All SiFive errata Kconfig depend on this Kconfig. Disabling
 	  this Kconfig will disable all SiFive errata. Please say "Y"
@@ -35,8 +34,7 @@ config ERRATA_SIFIVE_CIP_1200
 
 config ERRATA_THEAD
 	bool "T-HEAD errata"
-	depends on !XIP_KERNEL
-	select RISCV_ALTERNATIVE
+	depends on RISCV_ALTERNATIVE
 	help
 	  All T-HEAD errata Kconfig depend on this Kconfig. Disabling
 	  this Kconfig will disable all T-HEAD errata. Please say "Y"