RE: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on Hip06

[Gabriele Paoloni <gabriele.paoloni@huawei.com>]

Hi Liviu

> -----Original Message-----
> From: liviu.dudau@arm.com [mailto:liviu.dudau@arm.com]
> Sent: 11 November 2016 18:16
> To: Gabriele Paoloni
> Cc: Arnd Bergmann; linux-arm-kernel@lists.infradead.org; Yuanzhichang;
> mark.rutland@arm.com; devicetree@vger.kernel.org;
> lorenzo.pieralisi@arm.com; minyard@acm.org; linux-pci@vger.kernel.org;
> benh@kernel.crashing.org; John Garry; will.deacon@arm.com; linux-
> kernel@vger.kernel.org; xuwei (O); Linuxarm; zourongrong@gmail.com;
> robh+dt@kernel.org; kantyzc@163.com; linux-serial@vger.kernel.org;
> catalin.marinas@arm.com; olof@lixom.net; bhelgaas@googl e.com;
> zhichang.yuan02@gmail.com
> Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on
> Hip06
> 
> On Fri, Nov 11, 2016 at 03:53:53PM +0000, Gabriele Paoloni wrote:
> > Hi Liviu
> 
> Hi Gabriele,
> 
> >
> > > -----Original Message-----
> > > From: liviu.dudau@arm.com [mailto:liviu.dudau@arm.com]
> > > Sent: 11 November 2016 14:46
> > > To: Gabriele Paoloni
> > > Cc: Arnd Bergmann; linux-arm-kernel@lists.infradead.org;
> Yuanzhichang;
> > > mark.rutland@arm.com; devicetree@vger.kernel.org;
> > > lorenzo.pieralisi@arm.com; minyard@acm.org; linux-
> pci@vger.kernel.org;
> > > benh@kernel.crashing.org; John Garry; will.deacon@arm.com; linux-
> > > kernel@vger.kernel.org; xuwei (O); Linuxarm; zourongrong@gmail.com;
> > > robh+dt@kernel.org; kantyzc@163.com; linux-serial@vger.kernel.org;
> > > catalin.marinas@arm.com; olof@lixom.net; bhelgaas@googl e.com;
> > > zhichang.yuan02@gmail.com
> > > Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver implementation on
> > > Hip06
> > >
> > > On Fri, Nov 11, 2016 at 01:39:35PM +0000, Gabriele Paoloni wrote:
> > > > Hi Arnd
> > > >
> > > > > -----Original Message-----
> > > > > From: Arnd Bergmann [mailto:arnd@arndb.de]
> > > > > Sent: 10 November 2016 16:07
> > > > > To: Gabriele Paoloni
> > > > > Cc: linux-arm-kernel@lists.infradead.org; Yuanzhichang;
> > > > > mark.rutland@arm.com; devicetree@vger.kernel.org;
> > > > > lorenzo.pieralisi@arm.com; minyard@acm.org; linux-
> > > pci@vger.kernel.org;
> > > > > benh@kernel.crashing.org; John Garry; will.deacon@arm.com;
> linux-
> > > > > kernel@vger.kernel.org; xuwei (O); Linuxarm;
> zourongrong@gmail.com;
> > > > > robh+dt@kernel.org; kantyzc@163.com; linux-
> serial@vger.kernel.org;
> > > > > catalin.marinas@arm.com; olof@lixom.net; liviu.dudau@arm.com;
> > > > > bhelgaas@googl e.com; zhichang.yuan02@gmail.com
> > > > > Subject: Re: [PATCH V5 3/3] ARM64 LPC: LPC driver
> implementation on
> > > > > Hip06
> > > > >
> > > > > 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.
> > >
> > > Gabriele,
> > >
> > > >
> > > > I am not sure this would make sense...
> > > >
> > > > IMHO all the mechanism around io_range_list is needed to provide
> the
> > > > "mapping" between I/O tokens and physical CPU addresses.
> > > >
> > > > Currently the available tokens range from 0 to IO_SPACE_LIMIT.
> > > >
> > > > As you know the I/O memory accessors operate on whatever
> > > > __of_address_to_resource sets into the resource (start, end).
> > > >
> > > > With this special device in place we cannot know if a resource is
> > > > assigned with an I/O token or a physical address, unless we
> forbid
> > > > the I/O tokens to be in a specific range.
> > > >
> > > > So this is why we are changing the offsets of all the functions
> > > > handling io_range_list (to make sure that a range is forbidden to
> > > > the tokens and is available to the physical addresses).
> > > >
> > > > We have chosen this forbidden range to be [0, PCIBIOS_MIN_IO)
> > > > because this is the maximum physical I/O range that a non PCI
> device
> > > > can operate on and because we believe this does not impose much
> > > > restriction on the available I/O token range; that now is
> > > > [PCIBIOS_MIN_IO, IO_SPACE_LIMIT].
> > > > So we believe that the chosen forbidden range can accommodate
> > > > any special ISA bus device with no much constraint on the rest
> > > > of I/O tokens...
> > >
> > > Your idea is a good one, however you are abusing PCIBIOS_MIN_IO and
> you
> > > actually need another variable for "reserving" an area in the I/O
> space
> > > that can be used for physical addresses rather than I/O tokens.
> > >
> > > The one good example for using PCIBIOS_MIN_IO is when your
> > > platform/architecture
> > > does not support legacy ISA operations *at all*. In that case
> someone
> > > sets the PCIBIOS_MIN_IO to a non-zero value to reserve that I/O
> range
> > > so that it doesn't get used. With Zhichang's patch you now start
> > > forcing
> > > those platforms to have a valid address below PCIBIOS_MIN_IO.
> >
> > But if PCIBIOS_MIN_IO is 0 then it means that all I/O space is to be
> used
> > by PCI controllers only...
> 
> Nope, that is not what it means. It means that PCI devices can see I/O
> addresses
> on the bus that start from 0. There never was any usage for non-PCI
> controllers

So I am a bit confused...
>From http://www.firmware.org/1275/bindings/isa/isa0_4d.ps
It seems that ISA buses operate on cpu I/O address range [0, 0xFFF].
I thought that was the reason why for most architectures we have
PCIBIOS_MIN_IO equal to 0x1000 (so I thought that ISA controllers
usually use [0, PCIBIOS_MIN_IO - 1] )

For those architectures whose PCIBIOS_MIN_IO != 0x1000 probably
they are not fully compliant or they cannot fully support an ISA
controller...?

As said before this series forbid IO tokens to be in [0, PCIBIOS_MIN_IO)
to allow special ISA controllers to use that range with special
accessors.
Having a variable threshold would make life much more difficult
as there would be a probe dependency between the PCI controller and
the special ISA one (PCI to wait for the special ISA device to be
probed and set the right threshold value from DT or ACPI table).

Instead using PCIBIOS_MIN_IO is easier and should not impose much
constraint as [PCIBIOS_MIN_IO, IO_SPACE_LIMIT] is available to
the PCI controller for I/O tokens...

Thanks

Gab

> when PCIBIOS_MIN_IO != 0. That is what Zhichang is trying to do now and
> what
> I think is not the right thing (and not enough anyway).
> 
> > so if you have a special bus device using
> > an I/O range in this case should be a PCI controller...
> 
> That has always been the case. It is this series that wants to
> introduce the
> new meaning.
> 
> > i.e. I would
> > expect it to fall back into the case of I/O tokens redirection rather
> than
> > physical addresses redirection (as mentioned below from my previous
> reply).
> > What do you think?
> 
> I think you have looked too much at the code *with* Zhichang's patches
> applied.
> Take a step back and look at how PCIBIOS_MIN_IO is used now, before you
> apply
> the patches. It is all about PCI addresses and there is no notion of
> non-PCI
> busses using PCI framework. Only platforms and architectures that try
> to work
> around some legacy standards (ISA) or HW restrictions.
> 
> Best regards,
> Liviu
> 
> >
> > Thanks
> >
> > Gab
> >
> >
> > >
> > > For the general case you also have to bear in mind that
> PCIBIOS_MIN_IO
> > > could
> > > be zero. In that case, what is your "forbidden" range? [0, 0) ? So
> it
> > > makes
> > > sense to add a new #define that should only be defined by those
> > > architectures/
> > > platforms that want to reserve on top of PCIBIOS_MIN_IO another
> region
> > > where I/O tokens can't be generated for.
> > >
> > > Best regards,
> > > Liviu
> > >
> > > >
> > > > >
> > > > > > > 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.
> > > >
> > > > As I mentioned above, special devices operate on CPU addresses
> > > directly,
> > > > not I/O tokens. For them there is no way to distinguish....
> > > >
> > > > >
> > > > > 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.
> > > >
> > > > Ok so here you are talking about a platform that has got an I/O
> range
> > > > under the PCI host controller, right?
> > > > And this I/O range cannot be directly memory mapped but needs
> special
> > > > redirections for the I/O tokens, right?
> > > >
> > > > In this scenario registering the I/O ranges with the forbidden
> range
> > > > implemented by the current patch would still allow to redirect
> I/O
> > > > tokens as long as arm64_extio_ops->start >= PCIBIOS_MIN_IO
> > > >
> > > > So effectively the special PCI host controller
> > > > 1) knows the physical range that needs special redirection
> > > > 2) register such range
> > > > 3) uses pci_pio_to_address() to retrieve the IO tokens for the
> > > >    special accessors
> > > > 4) sets arm64_extio_ops->start/end to the IO tokens retrieved in
> 3)
> > > >
> > > > So to be honest I think this patch can fit well both with
> > > > special PCI controllers that need I/O tokens redirection and with
> > > > special non-PCI controllers that need non-PCI I/O physical
> > > > address redirection...
> > > >
> > > > Thanks (and sorry for the long reply but I didn't know how
> > > > to make the explanation shorter :) )
> > > >
> > > > Gab
> > > >
> > > > >
> > > > > If we separate the two steps:
> > > > >
> > > > > a) assign a range of logical I/O port numbers to a bus
> > > > > 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
> > >
> > > --
> > > ====================
> > > | I would like to |
> > > | fix the world,  |
> > > | but they're not |
> > > | giving me the   |
> > >  \ source code!  /
> > >   ---------------
> > >     ¯\_(ツ)_/¯
> 
> --
> ====================
> | I would like to |
> | fix the world,  |
> | but they're not |
> | giving me the   |
>  \ source code!  /
>   ---------------
>     ¯\_(ツ)_/¯