io-64-nonatomic: Add relaxed accessor variants

Whilst commit 9439eb3ab9d1 ("asm-generic: io: implement relaxed
accessor macros as conditional wrappers") makes the *_relaxed forms of
I/O accessors universally available to drivers, in cases where writeq()
is implemented via the io-64-nonatomic helpers, writeq_relaxed() will
end up falling back to writel() regardless of whether writel_relaxed()
is available (identically for s/write/read/).

Add corresponding relaxed forms of the nonatomic helpers to delegate
to the equivalent 32-bit accessors as appropriate. We also need to fix
io.h to avoid defining default relaxed variants if the basic accessors
themselves don't exist.

CC: Christoph Hellwig <[e-mail]>
CC: Darren Hart <[e-mail]>
CC: Hitoshi Mitake <[e-mail]>
Acked-by: Arnd Bergmann <[e-mail]>
Signed-off-by: Robin Murphy <[e-mail]>
Signed-off-by: Will Deacon <[e-mail]>

include/asm-generic/io.h

···
 #define readl_relaxed readl
 #endif
 
-#ifndef readq_relaxed
+#if defined(readq) && !defined(readq_relaxed)
 #define readq_relaxed readq
 #endif
 
···
 #define writel_relaxed writel
 #endif
 
-#ifndef writeq_relaxed
+#if defined(writeq) && !defined(writeq_relaxed)
 #define writeq_relaxed writeq
 #endif
 

include/linux/io-64-nonatomic-hi-lo.h

···
 	writel(val, addr);
 }
 
+static inline __u64 hi_lo_readq_relaxed(const volatile void __iomem *addr)
+{
+	const volatile u32 __iomem *p = addr;
+	u32 low, high;
+
+	high = readl_relaxed(p + 1);
+	low = readl_relaxed(p);
+
+	return low + ((u64)high << 32);
+}
+
+static inline void hi_lo_writeq_relaxed(__u64 val, volatile void __iomem *addr)
+{
+	writel_relaxed(val >> 32, addr + 4);
+	writel_relaxed(val, addr);
+}
+
 #ifndef readq
 #define readq hi_lo_readq
 #endif
 
 #ifndef writeq
 #define writeq hi_lo_writeq
+#endif
+
+#ifndef readq_relaxed
+#define readq_relaxed hi_lo_readq_relaxed
+#endif
+
+#ifndef writeq_relaxed
+#define writeq_relaxed hi_lo_writeq_relaxed
 #endif
 
 #endif	/* _LINUX_IO_64_NONATOMIC_HI_LO_H_ */

include/linux/io-64-nonatomic-lo-hi.h

···
 	writel(val >> 32, addr + 4);
 }
 
+static inline __u64 lo_hi_readq_relaxed(const volatile void __iomem *addr)
+{
+	const volatile u32 __iomem *p = addr;
+	u32 low, high;
+
+	low = readl_relaxed(p);
+	high = readl_relaxed(p + 1);
+
+	return low + ((u64)high << 32);
+}
+
+static inline void lo_hi_writeq_relaxed(__u64 val, volatile void __iomem *addr)
+{
+	writel_relaxed(val, addr);
+	writel_relaxed(val >> 32, addr + 4);
+}
+
 #ifndef readq
 #define readq lo_hi_readq
 #endif
 
 #ifndef writeq
 #define writeq lo_hi_writeq
+#endif
+
+#ifndef readq_relaxed
+#define readq_relaxed lo_hi_readq_relaxed
+#endif
+
+#ifndef writeq_relaxed
+#define writeq_relaxed lo_hi_writeq_relaxed
 #endif
 
 #endif	/* _LINUX_IO_64_NONATOMIC_LO_HI_H_ */