linux-kernel - Re: [PATCH 3/4] lib: logic_pio: Introduce MMIO_LOWER

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Date:   Mon, 27 Apr 2020 20:21:29 +0800
From:   Jiaxun Yang <jiaxun.yang@...goat.com>
To:     John Garry <john.garry@...wei.com>
Cc:     Arnd Bergmann <arnd@...db.de>, Bjorn Helgaas <bhelgaas@...gle.com>,
        <linux-mips@...r.kernel.org>,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        Huacai Chen <chenhc@...ote.com>,
        Paul Burton <paulburton@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Kitt <steve@....org>,
        Nick Desaulniers <ndesaulniers@...gle.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Anshuman Khandual <anshuman.khandual@....com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Daniel Silsby <dansilsby@...il.com>,
        Mike Rapoport <rppt@...ux.ibm.com>,
        Paul Cercueil <paul@...pouillou.net>,
        Mark Tomlinson <mark.tomlinson@...iedtelesis.co.nz>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Allison Randal <allison@...utok.net>,
        Tiezhu Yang <yangtiezhu@...ngson.cn>,
        Wei Xu <xuwei5@...ilicon.com>, <linux-kernel@...r.kernel.org>,
        Linuxarm <linuxarm@...wei.com>, Rob Herring <robh@...nel.org>,
        linux-arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH 3/4] lib: logic_pio: Introduce MMIO_LOWER_RESERVED

On Mon, 27 Apr 2020 12:54:06 +0100
John Garry <john.garry@...wei.com> wrote:

> On 27/04/2020 12:03, Jiaxun Yang wrote:
> > 
> > 
> > 于 2020年4月27日 GMT+08:00 下午6:43:09, John Garry
> > <john.garry@...wei.com> 写到:  
> >> On 26/04/2020 12:47, Jiaxun Yang wrote:  
> >>> That would allow platforms reserve some lower address in PIO MMIO
> >>> range to deal with legacy drivers with hardcoded I/O ports that
> >>> can't be managed by logic_pio.  
> >>
> >> Hi,
> >>
> >> Is there some reason why the logic_pio code cannot be improved to
> >> handle these devices at these "fixed" addresses? Or do you have a
> >> plan to improve it? We already support fixed bus address devices
> >> in the INDIRECT IO region.  
> > 
> > Hi,
> > 
> > The issue about "Fixed Address" is we can't control the ioport
> > That driver used to operate devices.
> > So any attempt to resolve it in logic_pio seems impossible.
> > 
> > Currently we have i8259, i8042, piix4_smbus, mc146818 rely on this
> > assumption.  
> 
> Right, and from glancing at a couple of drivers you mentioned, if we 
> were to register a logic pio region for that legacy region, there
> does not seem to be an easy place to fixup to use logic pio addresses
> (for those devices). They use hardcoded values. However if all those
> drivers were mips specific, you could fixup those drivers to use
> logic_pio addresses today through some macro. But not sure on that.
> 

Well, most of these drivers are shared with x86 so....
I guess the conversion needs two or more release cycles.

> 
> So, going back to your change, I have a dilemma wondering whether you 
> should still register a logic pio region for the legacy region
> instead of the carveout reservation, but ensure it is the first
> region registered, such that logic pio address base is 0 and no
> translation is required. At least then you have a region registered
> and it shows in /proc/ioports, but then this whole thing becomes a
> bit fragile.

Thanks for your solution. So I must register this range as early as
possible. As IRQ is the first subsystem using ISA, I'll do it before
IRQ init, just at the place I setup iormap for reserved region now.

Should be early enough to avoid any collision, as the only logic_pio
user on our system is PCI controller.

Thanks.
> 
--
Jiaxun Yang