linux-kernel - RE: Purpose of pci_remap

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Date:	Wed, 13 Jul 2016 08:11:56 +0000
From:	Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Liviu.Dudau@....com" <Liviu.Dudau@....com>,
	nofooter <nofooter@...inx.com>,
	"thomas.petazzoni@...e-electrons.com" 
	<thomas.petazzoni@...e-electrons.com>
Subject: RE: Purpose of pci_remap_iospace

> Subject: Re: Purpose of pci_remap_iospace
>
> On Tuesday, July 12, 2016 6:57:10 AM CEST Bharat Kumar Gogada wrote:
> > Hi,
> >
> > I have a query.
> >
> > Can any once explain the purpose of pci_remap_iospace function in root
> port driver.
> >
> > What is its dependency with architecture ?
> >
> > Here is my understanding, the above API takes PCIe IO resource and its
> > to be mapped CPU address from ranges property and remaps into virtual
> address space.
> >
> > So my question is who uses this virtual addresses ?
>
> The inb()/outb() functions declared in asm/io.h
>
> > When End Point requests for IO BARs doesn't it get from the above
> > resource range (first parameter of API) and do ioremap to access this
> > region ?
>
> Device drivers generally do not ioremap() the I/O BARs but they use
> inb()/outb() directly. They can also call pci_iomap() and do
> ioread8()/iowrite8() on the pointer returned from that function, but
> generally the call to pci_iomap() then returns a pointer into the virtual
> address that is already mapped.
>
> > But why root complex driver is mapping this address region ?
>
> The PCI core does not know that the I/O space is memory mapped.
> On x86 and a few others, I/O space is not memory mapped but requires the
> use of special CPU instructions.
>
Thanks Arnd.

I'm facing issue in testing IO bars on our SoC.

I added following ranges in our device tree :
ranges = <0x01000000 0x00000000 0x00000000 0x00000000 0xe0000000 0 0x00100000   //io
             0x02000000 0x00000000 0xe0100000 0x00000000 0xe0100000 0 0x0ef00000>;   //non prefetchabe memory

And I'm using above API to map the res and cpu physical address in my driver.

Kernel Boot log:
[    2.345294] nwl-pcie fd0e0000.pcie: Link is UP
[    2.345339] PCI host bridge /amba/pcie@...e0000 ranges:
[    2.345356]   No bus range found for /amba/pcie@...e0000, using [bus 00-ff]
[    2.345382]    IO 0xe0000000..0xe00fffff -> 0x00000000
[    2.345401]   MEM 0xe0100000..0xeeffffff -> 0xe0100000
[    2.345498] nwl-pcie fd0e0000.pcie: PCI host bridge to bus 0000:00
[    2.345517] pci_bus 0000:00: root bus resource [bus 00-ff]
[    2.345533] pci_bus 0000:00: root bus resource [io  0x0000-0xfffff]
[    2.345550] pci_bus 0000:00: root bus resource [mem 0xe0100000-0xeeffffff]
[    2.345770] pci 0000:00:00.0: cannot attach to SMMU, is it on the same bus?
[    2.345786] iommu: Adding device 0000:00:00.0 to group 1
[    2.346142] pci 0000:01:00.0: cannot attach to SMMU, is it on the same bus?
[    2.346158] iommu: Adding device 0000:01:00.0 to group 1
[    2.346213] pci 0000:00:00.0: BAR 8: assigned [mem 0xe0100000-0xe02fffff]
[    2.346234] pci 0000:01:00.0: BAR 0: assigned [mem 0xe0100000-0xe01fffff 64bit]
[    2.346268] pci 0000:01:00.0: BAR 2: assigned [mem 0xe0200000-0xe02fffff 64bit]
[    2.346300] pci 0000:01:00.0: BAR 4: no space for [io  size 0x0040]
[    2.346316] pci 0000:01:00.0: BAR 4: failed to assign [io  size 0x0040]
[    2.346333] pci 0000:00:00.0: PCI bridge to [bus 01-0c]
[    2.346350] pci 0000:00:00.0:   bridge window [mem 0xe0100000-0xe02fffff]

IO assignment fails.

On End Point:
01:00.0 Memory controller: Xilinx Corporation Device a024
        Subsystem: Xilinx Corporation Device 0007
        Control: I/O- Mem- BusMaster- SpecCycle- MemWINV- VGASnoop- ParErr- Stepping- SERR- FastB2B- DisINTx-
        Status: Cap+ 66MHz- UDF- FastB2B- ParErr- DEVSEL=fast >TAbort- <TAbort- <MAbort- >SERR- <PERR- INTx-
        Interrupt: pin A routed to IRQ 224
        Region 0: Memory at e0100000 (64-bit, non-prefetchable) [disabled] [size=1M]
        Region 2: Memory at e0200000 (64-bit, non-prefetchable) [disabled] [size=1M]
        Region 4: I/O ports at <unassigned> [disabled]

When I tested on x86 machine the same End Point I/O address is assigned, but it is a IO port mapped address.

So my doubt is why the memory mapped IO addresses are not assigned to EP on SoC ?

Do we need to have port mapped addresses on SoC also for PCI IO bars ?

Please let me know If I'm doing something wrong or missing something.

Thanks & Regards,
Bharat



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