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

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Date:   Tue, 3 Mar 2020 13:18:21 +0000
From:   John Garry <john.garry@...wei.com>
To:     Sinan Kaya <okaya@...nel.org>, Arnd Bergmann <arnd@...db.de>
CC:     "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>
Subject: Re: About commit "io: change inX() to have their own IO barrier
 overrides"

+ linux-arch

For background, see 
https://lore.kernel.org/lkml/2e80d7bc-32a0-cc40-00a9-8a383a1966c2@huawei.com/

>>
>> So today only ARM64 uses it for this relevant code, above. But maybe
>> others in future will want to use it - any arch without native IO port
>> access is a candidate.
> 
> I'm looking at Arnd here for help.
> 
>>
>>>
>>> As long as the expectations are set, I see no reason why it shouldn't
>>> but, I'll let Arnd comment on it too.
>>
>> ok, so it looks reasonable consider replicating your change for ***, above.

To be clear, I would make this change in lib/logic_pio.c since 
__io_pbr() can be overridden per-arch:

  #define BUILD_LOGIC_IO(bw, type)
  type logic_in##bw(unsigned long addr)
  {
       type ret = (type)~0;
       if (addr < MMIO_UPPER_LIMIT) {
-          ret = read##bw(PCI_IOBASE + addr);
+          __io_pbr();
+          ret = __raw_read##bw(PCI_IOBASE + addr);
+          __io_pbr();	
       } else if (addr >= MMIO_UPPER_LIMIT && addr < IO_SPACE_LIMIT) {
           struct logic_pio_hwaddr *entry = find_io_range(addr);

...

(forgetting leX_to_cpu for the moment)

> 
> Arnd is the maintainer here. We should consult first.

ok, fine.

> I believe there is also a linux-arch mailing list. Going there with this
> question makes sense IMO.

Cheers,
John