linux-kernel - Re: Questions about logic

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Date:   Sat, 22 Feb 2020 00:47:39 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     John Garry <john.garry@...wei.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



于 2020年2月21日 GMT+08:00 下午7:49:45, John Garry <john.garry@...wei.com> 写到:
>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.

In MIPS, PCI Host Bridge share PIO region with legacy devices.

Probably the better solution is to add a kind of logic pio region called FIXED_MMIO,
so we can occupy some low ioports for these fixed devices at boot time.

A ISA bridge node in DeviceTree can be used
to express this region.

I'm going to work on this and try to make a RFC patch later.

Thanks for your help again!
>
>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.

Well, it can be higher or lower, whatever.

>
>> 
>> 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

-- 
Jiaxun Yang