linux-kernel - Re: About commit "io: change inX() to have their own IO barrier overrides"

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Date:   Fri, 6 Mar 2020 17:29:26 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     John Garry <john.garry@...wei.com>
Cc:     Sinan Kaya <okaya@...nel.org>, "xuwei (O)" <xuwei5@...ilicon.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Jiaxun Yang <jiaxun.yang@...goat.com>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Will Deacon <will@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>
Subject: Re: About commit "io: change inX() to have their own IO barrier overrides"

On Fri, Mar 6, 2020 at 5:18 PM John Garry <john.garry@...wei.com> wrote:
> On 06/03/2020 15:16, Arnd Bergmann wrote:
> > On Fri, Mar 6, 2020 at 11:40 AM John Garry <john.garry@...wei.com> wrote:
> >> On 06/03/2020 07:54, Arnd Bergmann wrote:
> >>> On Fri, Mar 6, 2020 at 4:44 AM Sinan Kaya <okaya@...nel.org> wrote:
> >> -- a/lib/logic_pio.c
> >> +++ b/lib/logic_pio.c
> >> @@ -229,13 +229,21 @@ unsigned long
> >> logic_pio_trans_cpuaddr(resource_size_t addr)
> >>    }
> >>
> >>    #if defined(CONFIG_INDIRECT_PIO) && defined(PCI_IOBASE)
> >> +
> >> +#define logic_in_to_cpu_b(x) (x)
> >> +#define logic_in_to_cpu_w(x) __le16_to_cpu(x)
> >> +#define logic_in_to_cpu_l(x) __le32_to_cpu(x)
> >> +
> >>    #define BUILD_LOGIC_IO(bw, type)                                      \
>
> Note: The "bw" argument name could be improved to "bwl", since this
> macro is used for building inl() also.
>
> >>    type logic_in##bw(unsigned long addr)                                 \
> >>    {                                                                     \
> >>           type ret = (type)~0;                                           \
> >>                                                                          \
> >>           if (addr < MMIO_UPPER_LIMIT) {                                 \
> >> -               ret = read##bw(PCI_IOBASE + addr);                     \
> >> +               void __iomem *_addr = PCI_IOBASE + addr;               \
> >> +               __io_pbr();                                            \
> >> +               ret = logic_in_to_cpu_##bw(__raw_read##bw(_addr));     \
> >> +               __io_par(ret);                                         \
> >>           } else if (addr >= MMIO_UPPER_LIMIT && addr < IO_SPACE_LIMIT) {\
> >>                   struct logic_pio_hwaddr *entry = find_io_rang
> >>
> >> We could prob combine the le_to_cpu and __raw_read into a single macro.
> >
> > What is the purpose of splitting out the byteswap rather than leaving the
> > open-coded rather than __le16_to_cpu(__raw_readw(PCI_IOBASE + addr))?
>
> I'm just copying what is in asm-generic io.h, which uses the 16b and 32b
> byteswaps in the w and l variants, respectively.

Sure, but I don't think that needs another macro.

>
> The idea is good, but it would be nice if we just somehow use a common
> asm-generic io.h definition directly in logic_pio.c, like:
>
> asm-generic io.h:
>
> #ifndef __raw_inw // name?
> #define __raw_inw __raw_inw
> static inline u16 __raw_inw(unsigned long addr)
> {
>         u16 val;
>
>         __io_pbr();
>         val = __le16_to_cpu(__raw_readw(addr));
>         __io_par(val);
>         return val;
> }
> #endif
>
> #include <linux/logic_pio.h>
>
> #ifndef inw
> #define inw __raw_inw
> #endif

Yes, makes sense. Maybe __arch_inw() then? Not great either, but I think
that's better than __raw_inw() because __raw_* would sound like it
mirrors __raw_readl() that lacks the barriers and byteswaps.

      Arnd