linux-kernel - Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to __io

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Message-ID: <mhng-30e76674-df9d-4689-8c77-3a3b4723ee24@palmer-si-x1c4>
Date:   Wed, 13 Feb 2019 13:57:50 -0800 (PST)
From:   Palmer Dabbelt <palmer@...ive.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     Will Deacon <will.deacon@....com>, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org, andrew.murray@....com,
        catalin.marinas@....com, linux-riscv@...ts.infradead.org,
        aou@...s.berkeley.edu
Subject:     Re: [PATCH 1/2] asm-generic/io: Pass result on inX() accessor to __io_par()

On Wed, 13 Feb 2019 12:59:28 PST (-0800), Arnd Bergmann wrote:
> On Wed, Feb 13, 2019 at 6:46 PM Will Deacon <will.deacon@....com> wrote:
>
>> On Tue, Feb 12, 2019 at 12:55:17PM +0100, Arnd Bergmann wrote:
>>
>> > For all I can see, this should not conflict with the usage of the
>> > same macros on RISC-V, though it does make add a significant
>> > difference, so I'd like to see an Ack from the RISC-V folks as
>> > well (added to Cc), or possibly a change to arch/riscv/include/asm/io.h
>> > to do a corresponding change.

Thanks, the original patches didn't make it through my filters.

>> There's already a comment in that header which says that the accesses are
>> ordered wrt timer reads, so I don't think anything needs to change there.
>> For consistency with the macro arguments, I could augment their __io_par to
>> take the read value as an unused argument, if that's what you mean?

FWIW, we don't really have a way to mandate this in the ISA yet as there's no 
formal model for either CSR orderings or the IO memory space.  

> Yes, that's what I meant, I should have been clearer there.

That sounds reasonable to me.  It looks like we can also go ahead and delete a 
bunch of arch/riscv/include/asm/io.h now that this stuff is in asm-generic, 
which would cause us to actually start using these things.  I didn't know this 
had all been moved to asm-generic otherwise I would have cleaned this up 
earlier.

I think this should do it, but this does bring up a bit of an issue: the RISC-V 
versions of reads and friends put barriers outside the loop, while the 
asm-generic version don't.  What are these actually supposed to do?

Either way that resolves, feel free to consider something like

diff --git a/arch/riscv/include/asm/io.h b/arch/riscv/include/asm/io.h
index b269451e7e85..378975f180a7 100644
--- a/arch/riscv/include/asm/io.h
+++ b/arch/riscv/include/asm/io.h
@@ -198,20 +198,20 @@ static inline u64 __raw_readq(const volatile void __iomem *addr)
  * writes.
  */
 #define __io_pbr()	__asm__ __volatile__ ("fence io,i"  : : : "memory");
-#define __io_par()	__asm__ __volatile__ ("fence i,ior" : : : "memory");
+#define __io_par(v)	__asm__ __volatile__ ("fence i,ior" : : : "memory");
 #define __io_pbw()	__asm__ __volatile__ ("fence iow,o" : : : "memory");
 #define __io_paw()	__asm__ __volatile__ ("fence o,io"  : : : "memory");

-#define inb(c)		({ u8  __v; __io_pbr(); __v = readb_cpu((void*)(PCI_IOBASE + (c))); __io_par(); __v; })
-#define inw(c)		({ u16 __v; __io_pbr(); __v = readw_cpu((void*)(PCI_IOBASE + (c))); __io_par(); __v; })
-#define inl(c)		({ u32 __v; __io_pbr(); __v = readl_cpu((void*)(PCI_IOBASE + (c))); __io_par(); __v; })
+#define inb(c)		({ u8  __v; __io_pbr(); __v = readb_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
+#define inw(c)		({ u16 __v; __io_pbr(); __v = readw_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })
+#define inl(c)		({ u32 __v; __io_pbr(); __v = readl_cpu((void*)(PCI_IOBASE + (c))); __io_par(__v); __v; })

 #define outb(v,c)	({ __io_pbw(); writeb_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
 #define outw(v,c)	({ __io_pbw(); writew_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })
 #define outl(v,c)	({ __io_pbw(); writel_cpu((v),(void*)(PCI_IOBASE + (c))); __io_paw(); })

 #ifdef CONFIG_64BIT
-#define inq(c)		({ u64 __v; __io_pbr(); __v = readq_cpu((void*)(c)); __io_par(); __v; })
+#define inq(c)		({ u64 __v; __io_pbr(); __v = readq_cpu((void*)(c)); __io_par(__v); __v; })
 #define outq(v,c)	({ __io_pbw(); writeq_cpu((v),(void*)(c)); __io_paw(); })
 #endif

@@ -261,9 +261,9 @@ __io_reads_ins(reads, u32, l, __io_br(), __io_ar())
 #define readsw(addr, buffer, count) __readsw(addr, buffer, count)
 #define readsl(addr, buffer, count) __readsl(addr, buffer, count)

-__io_reads_ins(ins,  u8, b, __io_pbr(), __io_par())
-__io_reads_ins(ins, u16, w, __io_pbr(), __io_par())
-__io_reads_ins(ins, u32, l, __io_pbr(), __io_par())
+__io_reads_ins(ins,  u8, b, __io_pbr(), __io_par(addr))
+__io_reads_ins(ins, u16, w, __io_pbr(), __io_par(addr))
+__io_reads_ins(ins, u32, l, __io_pbr(), __io_par(addr))
 #define insb(addr, buffer, count) __insb((void __iomem *)(long)addr, buffer, count)
 #define insw(addr, buffer, count) __insw((void __iomem *)(long)addr, buffer, count)
 #define insl(addr, buffer, count) __insl((void __iomem *)(long)addr, buffer, count)

as

Revewied-by: Palmer Dabbelt <palmer@...ive.com>

when included along with the other diff.  That way we can at least keep the 
macro signatures matching, the cleanup can come later...

Thanks!