Date:   Thu, 20 Feb 2020 14:23:57 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
CC:     Wei Xu <xuwei5@...ilicon.com>, bhelgaas <bhelgaas@...gle.com>,
        andyshevchenko <andy.shevchenko@...il.com>,
        Arnd Bergmann <arnd@...db.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Linux Mips <linux-mips@...r.kernel.org>
Subject: Re: Questions about logic_pio

> Also Cc MIPS list to check other's opinions.
> 
> Hi John.
> 

Hi Jiaxun Yang,

> Thanks for your kind explanation, however, I think this way is
> violating how I/O ports supposed to work, at least in MIPS world.

For a bit more history, please understand that the core PCI code was 
managing non-native IO port space in the same way before we added the 
logic PIO framework. The only real functional change here was that we 
introduced the indirect-io region within the IO port space, under 
CONFIG_INDIRECT_PIO.

> 
>   > >>
>   > >> After dig into logic pio logic, I found that logic pio is trying to "allocate" an io_start
>   > >> for MMIO ranges, the allocation starts from 0x0. And later the io_start is used to calculate
>   > >> cpu_address.  In my opinion, for direct MMIO access, logic_pio address should always
>   > >> equal to hw address,
>   >
>   > I'm not sure what you mean by simply the hw address.
>   >
> 
> I meant  hw_start should always equal to io_start.
> 
> 
> MIPS have their own wrapped inl/outl functions, 

Can you please point me to these? I could not find them in arch/mips

I will also note that arch/mips/include/asm/io.h does not include 
asm-generic io.h today

doing the samething with
> PCI_IOBASE enabled one. I was just trying to use PCI_IOBASE instead.
> 
> Originally, the I/O ports layout seems like this:
> 
> 00000020-00000021 : pic1
> 00000060-0000006f : i8042
> 00000070-00000077 : rtc0
> 000000a0-000000a1 : pic2
> 00000170-00000177 : pata_atiixp
> 000001f0-000001f7 : pata_atiixp
> 00000376-00000376 : pata_atiixp
> 000003f6-000003f6 : pata_atiixp
> 00000800-000008ff : acpi
> 00001000-00001008 : piix4_smbus
> 00004000-0003ffff : pci io space
>    00004000-00004fff : PCI Bus 0000:01
>      00004000-000040ff : 0000:01:05.0
>    00005000-00005fff : PCI Bus 0000:03
>      00005000-0000501f : 0000:03:00.0
> 
> But with PCI_IOBASE defined, I got this:
> 
> host bridge /bus@...00000/pci@...00000 ranges:
>        MEM 0x0040000000..0x007fffffff -> 0x0040000000
>         IO 0x0000004000..0x0000007fff -> 0x0000004000
> resource collision: [io  0x0000-0x3fff] conflicts with pic1 [io  0x0020-0x0021]
> 
> Because io_start was allocated to 0x0 by Logic PIO.
> 
> There are a lot of devices that have fixed ioports thanks to x86's legacy.

Well, yes, I'm not so surprised.

So if MIPS does not have native IO port access, then surely you need 
some host bridge to translate host CPU MMIO accesses to port I/O 
accesses, right? Where are these CPU addresses defined?

> For example, in my hardware, ioports for RTC, PIC, I8042 are unmoveable,
> and they can't be managed by logic pio subsystem. > Also, the PCI Hostbridge got implied by DeviceTree that it's I/O range
> started from 0x4000 in bus side

which bus is this?

, but then, Logic PIO remapped to PCI_IOBASE + 0x0.
> The real address should be PCI_IOBASE + 0x4000,

You seem to be using two methods to manage IO port space, and they seem 
to be conflicting.

> hardware never got correctly informed about that. And there is still no way to
> transform to correct address as it's inside the MMIO_LIMIT.
> 
> So the question comes to why we're allocating io_start for MMIO PCI_IOBASE
> rather than just check the range provided doesn't overlap each other or exceed
> the MMIO_LIMIT.

When PCI_IOBASE is defined, we work on the basis that any IO port range 
in the system is registered for a logical PIO region, which manages the 
actual IO port addresses - see logic_pio_trans_cpuaddr().

Thanks,
John

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