linux-kernel - Re: Questions about logic

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Message-ID: <65fffffa-2c74-aa09-7fdb-29a7200d7ac4@huawei.com>
Date:   Fri, 21 Feb 2020 11:49:45 +0000
From:   John Garry <john.garry@...wei.com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
CC:     "xuwei (O)" <xuwei5@...wei.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

On 21/02/2020 00:42, Jiaxun Yang wrote:
>   >
>   > I will add this may not cover your need, as you probably cannot deal
>   > with any logical PIO <-> ISA translation without modifying the device
>   > driver. For this, we may need to reserve the first 0x4000 in logical PIO
>   > space for this sort of legacy host.
> 
> Hi,
> 
> After thinking twice, I realized that the most convenient way for me is
> adding an option to get rid of the mess of logic PIO. MIPS system is emulating
> x86's behavior, while logic PIO isn't designed for such platform.

It was designed for archs which define PCI_IOBASE for PCI MMIO-based or 
IndirectIO-based IO port access.

> 
> Or probably I need a variation of Logic PIO, which leave MMIO space AS-IS
> (not try to reallocate it)

That does not work if add a PCI host with MMIO-based IO port regions 
into the mix.

It only so happens today that for mips you have a single MMIO-based IO 
port region, and you have IO port base for that region conveniently @ 
0x0. Then your drivers can have fixed IO port addresses.

For dealing with multiple MMIO-based IO ports regions - which is the 
case for PCI host bridges - then you need to map those MMIO-based IO 
port regions to different regions in IO port space.

> but still preserving higher 0x4000 for indirect access.

Then there is no space for PCI MMIO-based IO ports.

> 
> Thanks a lot!
>   >
>   > That would not be a bad thing - see
>   >https://lore.kernel.org/linux-pci/1560262374-67875-1-git-send-email-john.garry@huawei.com/
>   >
>   >
>   > >
>   > > This driver deals with legacy IO ports where we need to bitbang