linux-kernel - Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on Hip06

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Date:   Fri, 11 Nov 2016 10:48:57 +0000
From:   "liviu.dudau@....com" <liviu.dudau@....com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Yuanzhichang <yuanzhichang@...ilicon.com>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "minyard@....org" <minyard@....org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "benh@...nel.crashing.org" <benh@...nel.crashing.org>,
        John Garry <john.garry@...wei.com>,
        "will.deacon@....com" <will.deacon@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "xuwei (O)" <xuwei5@...ilicon.com>, Linuxarm <linuxarm@...wei.com>,
        "zourongrong@...il.com" <zourongrong@...il.com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "kantyzc@....com" <kantyzc@....com>,
        "linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
        "catalin.marinas@....com" <catalin.marinas@....com>,
        "olof@...om.net" <olof@...om.net>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "zhichang.yuan02@...il.com" <zhichang.yuan02@...il.com>
Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on Hip06

Hi Arnd,

On Thu, Nov 10, 2016 at 05:07:21PM +0100, Arnd Bergmann wrote:
> On Thursday, November 10, 2016 3:36:49 PM CET Gabriele Paoloni wrote:
> > 
> > Where should we get the range from? For LPC we know that it is going
> > Work on anything that is not used by PCI I/O space, and this is 
> > why we use [0, PCIBIOS_MIN_IO]
> 
> It should be allocated the same way we allocate PCI config space
> segments. This is currently done with the io_range list in
> drivers/pci/pci.c, which isn't perfect but could be extended
> if necessary. Based on what others commented here, I'd rather
> make the differences between ISA/LPC and PCI I/O ranges smaller
> than larger.
> 
> > > Your current version has
> > > 
> > >         if (arm64_extio_ops->pfout)                             \
> > >                 arm64_extio_ops->pfout(arm64_extio_ops->devpara,\
> > >                        addr, value, sizeof(type));             \
> > > 
> > > Instead, just subtract the start of the range from the logical
> > > port number to transform it back into a bus-local port number:
> > 
> > These accessors do not operate on IO tokens:
> > 
> > If (arm64_extio_ops->start > addr || arm64_extio_ops->end < addr)
> > addr is not going to be an I/O token; in fact patch 2/3 imposes that
> > the I/O tokens will start at PCIBIOS_MIN_IO. So from 0 to PCIBIOS_MIN_IO
> > we have free physical addresses that the accessors can operate on.
> 
> Ah, I missed that part. I'd rather not use PCIBIOS_MIN_IO to refer to
> the logical I/O tokens, the purpose of that macro is really meant
> for allocating PCI I/O port numbers within the address space of
> one bus.
> 
> Note that it's equally likely that whichever next platform needs
> non-mapped I/O access like this actually needs them for PCI I/O space,
> and that will use it on addresses registered to a PCI host bridge.
> 
> If we separate the two steps:
> 
> a) assign a range of logical I/O port numbers to a bus

Except that currently when we add ranges to io_range_list we don't have
a bus number yet, because the parsing happens before the host bridge
has been created. Maybe register_io_range() can take a bus number as an
argument, but I'm not sure how we are going to use that in pci_pio_to_address()
or pci_address_to_pio().

Best regards,
Liviu

> b) register a set of helpers for redirecting logical I/O
>    port to a helper function
> 
> then I think the code will get cleaner and more flexible.
> It should actually then be able to replace the powerpc
> specific implementation.
> 
> 	Arnd

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