mm: Remove broken pfn_to_virt() on arch csky/hexagon/openrisc

Remove the broken pfn_to_virt() on architectures csky/hexagon/openrisc.

The pfn_to_virt() on those architectures takes PFN instead of PA as the
input to macro __va(), with PAGE_SHIFT applying to the converted VA, which
is not right, especially when there's a non-zero offset in __va(). [1]

The broken pfn_to_virt() was noticed when checking how page_to_virt() is
unfolded on x86. It turns out that the one in linux/mm.h instead of in
asm-generic/page.h is compiled for x86. However, page_to_virt() in
asm-generic/page.h is found out expanding to pfn_to_virt() with a bug
described above. The pfn_to_virt() is found out not right as well on
architectures csky/hexagon/openrisc.

Since there's no single caller on csky/hexagon/openrisc to pfn_to_virt()
and there are functions doing similar things as pfn_to_virt() --
- pfn_to_kaddr() in asm/page.h for csky,
- page_to_virt() in asm/page.h for hexagon, and
- page_to_virt() in linux/mm.h for openrisc,
just delete the pfn_to_virt() on those architectures.

The pfn_to_virt() in asm-generic/page.h is not touched in this patch as
it's referenced by page_to_virt() in that header while the whole header is
going to be removed as a whole due to no one including it.

Link:https://lore.kernel.org/all/20240131055159.2506-1-yan.y.zhao@intel.com [1]

Cc: Linus Walleij <linus.walleij@linaro.org>
Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Yan Zhao <yan.y.zhao@intel.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>

Author: yanzhao56

arch/csky/include/asm/page.h

@@ -82,11 +82,6 @@ static inline unsigned long virt_to_pfn(const void *kaddr)
 	return __pa(kaddr) >> PAGE_SHIFT;
 }
 
-static inline void * pfn_to_virt(unsigned long pfn)
-{
-	return (void *)((unsigned long)__va(pfn) << PAGE_SHIFT);
-}
-
 #define MAP_NR(x)	PFN_DOWN((unsigned long)(x) - PAGE_OFFSET - \
 				 PHYS_OFFSET_OFFSET)
 #define virt_to_page(x)	(mem_map + MAP_NR(x))

arch/hexagon/include/asm/page.h

@@ -133,12 +133,6 @@ static inline unsigned long virt_to_pfn(const void *kaddr)
 	return __pa(kaddr) >> PAGE_SHIFT;
 }
 
-static inline void *pfn_to_virt(unsigned long pfn)
-{
-	return (void *)((unsigned long)__va(pfn) << PAGE_SHIFT);
-}
-
-
 #define page_to_virt(page)	__va(page_to_phys(page))
 
 #include <asm/mem-layout.h>

arch/openrisc/include/asm/page.h

@@ -77,11 +77,6 @@ static inline unsigned long virt_to_pfn(const void *kaddr)
 	return __pa(kaddr) >> PAGE_SHIFT;
 }
 
-static inline void * pfn_to_virt(unsigned long pfn)
-{
-	return (void *)((unsigned long)__va(pfn) << PAGE_SHIFT);
-}
-
 #define virt_to_page(addr) \
 	(mem_map + (((unsigned long)(addr)-PAGE_OFFSET) >> PAGE_SHIFT))