Hi Zhichang

-----Original Message-----
From: zhichang [mailto:zhichang.yuan02 at gmail.com]
Sent: 21 September 2016 11:09
To: Arnd Bergmann; linux-arm-kernel at lists.infradead.org
Cc: Gabriele Paoloni; devicetree at vger.kernel.org;
lorenzo.pieralisi at arm.com; minyard at acm.org; linux-pci at vger.kernel.org;
gregkh at linuxfoundation.org; John Garry; will.deacon at arm.com; linux-
kernel at vger.kernel.org; Yuanzhichang; Linuxarm; xuwei (O); linux-
serial at vger.kernel.org; benh at kernel.crashing.org;
zourongrong at gmail.com; liviu.dudau at arm.com; kantyzc at 163.com
Subject: Re: [PATCH V3 2/4] ARM64 LPC: LPC driver implementation on
Hip06

Hi, Arnd,



On 2016?09?15? 20:24, Arnd Bergmann wrote:

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On Thursday, September 15, 2016 12:05:51 PM CEST Gabriele Paoloni

wrote:

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-----Original Message-----
On Thursday, September 15, 2016 8:02:27 AM CEST Gabriele Paoloni

wrote:

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From <<3.1.1. Open Firmware Properties for Bus Nodes>> in
http://www.firmware.org/1275/bindings/isa/isa0_4d.ps

I quote:
"There shall be an entry in the "ranges" property for each
of the Memory and/or I/O spaces if that address space is
mapped through the bridge."

It seems to me that it is ok to have 1:1 address mapping and that
therefore of_translate_address() should fail if "ranges" is not
present.

The key here is the definition of "mapped through the bridge".
I can only understand this as "directly mapped", i.e. an I/O
port of the child bus corresponds directly to a memory address
on the parent bus, but this is not the case here.

The problem with adding the mapping here is that it looks
like it should be valid to create a page table entry for
the address returned from the translation and access it through
a pointer dereference, but that is clearly not possible.

I understand that somehow we are abusing of the ranges property
here however the point is that with the current implementation

ranges

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is needed because otherwise the ipmi driver probe will fail here:

of_ipmi_probe -> of_address_to_resource -> __of_address_to_resource
-> of_translate_address -> __of_translate_address

Now we had a bit of discussion internally and to avoid
having ranges we came up with two possible solutions:

1) Using bit 3 of phys.hi cell in 2.2.1 of
http://www.firmware.org/1275/bindings/isa/isa0_4d.ps
This would mean reworking of_bus_isa_get_flags in
http://lxr.free-electrons.com/source/drivers/of/address.c#L398
and setting a new flag to be checked in __of_address_to_resource

2) Adding a property in the bindings of each device that is
a child of our LPC bus and modify __of_address_to_resource
to check if the property is in the DT and eventually bypass
of_translate_address

However in both 1) and 2) there are some issues:
in 1) we are not complying with the isa binding doc (we use
a bit that should be zero); in 2) we need to modify the
bindings documentation of the devices that are connected
to our LPC controller (therefore modifying other devices
bindings to fit our special case).

I think that maybe having the 1:1 range mapping doesn't
reflect well the reality but it is the less painful
solution...

What's your view?

We can check the 'i' bit for I/O space in of_bus_isa_get_flags,
and that should be enough to translate the I/O port number.

The only part we need to change here is to not go through
the crazy conversion all the way from PCI I/O space to a
physical address and back to a (logical) port number
that we do today with of_translate_address/pci_address_to_pio.

Sorry for the late response! Several days' leave....
Do you want to bypass of_translate_address and pci_address_to_pio for
the registered specific PIO?
I think the bypass for of_translate_address is ok, but worry some new
issues will emerge without the
conversion between physical address and logical/linux port number.

When PCI host bridge which support IO operations is configured and
enabled, the pci_address_to_pio will
populate the logical IO range from ZERO for the first host bridge. Our
LPC will also use part of the IO range
started from ZERO. It will make in/out enter the wrong branch possibly.

In V2, the 0 - 0x1000 logical IO range is reserved for LPC use only.
But it seems not so good. In this way,
PCI has no chance to use low 4K IO range(logical).

So, in V3, applying the conversion from physical/cpu address to
logical/linux IO port for any IO ranges,
including the LPC, but recorded the logical IO range for LPC. When
calling in/out with a logical port address,
we can check this port fall into LPC logical IO range and get back the
real IO.

Do you have further comments about this??

I think there are two separate issues to be discussed:

The first issue is about having of_translate_address failing due to
"range" missing. About this Arnd suggested that it is not appropriate
to have a range describing a bridge 1:1 mapping and this was discussed
before in this thread. Arnd had a suggestion about this (see below) 
however (looking twice at the code) it seems to me that such solution 
would lead to quite some duplication from __of_translate_address()
in order to retrieve the actual addr from dt...

I think extending of_empty_ranges_quirk() may be a reasonable solution.
What do you think Arnd?
  
The second issue is a conflict between cpu addresses used by the LPC
controller and i/o tokens from pci endpoints.

About this what if we modify armn64_extio_ops to have a list of ranges
rather than only one range (now we have just start/end); then in the
LPC driver we can scan the LPC child devices and 
1) populate such list of ranges
2) call pci_register_io_range for such ranges

Then when calling __of_address_to_resource we retrieve I/O tokens 
for the devices on top of the LPC driver and in the I/O accessors
we call pci_pio_to_address to figure out the cpu address and compare
it to the list of ranges in armn64_extio_ops.
  
What about this?

Thanks

Gab

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I can think of a several of ways to fix __of_address_to_resource
to just do the right thing according to the ISA binding to
make the normal drivers work.

The easiest solution is probably to hook into the
"taddr == OF_BAD_ADDR" case in __of_address_to_resource
and add a lookup for ISA buses there, and instead check
if some special I/O port operations were registered
for the port number, using an architecture specific
function that arm64 implements. Other architectures
like x86 that don't have a direct mapping between I/O
ports and MMIO addresses would implement that same
function differently.

What about add the specific quirk for Hip06 LPC in
of_empty_ranges_quirk()??

you know, there are several cases in which of_translate_address return
OF_BAD_ADDR.
And if we only check the special port range, it seems a bit risky. If
some device want to use this port range
when no hip06 LPC is configured, the checking does not work. I think we
should also check the relevant device.


Best,
Zhichang

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	Arnd