On 12/20/2017 11:26 PM, Ard Biesheuvel wrote:
On 20 December 2017 at 15:17, gary guo <[email protected]> wrote:
On Wed, Dec 20, 2017 at 09:13:58AM +0000, Ard Biesheuvel wrote:
Hi Heyi,
On 20 December 2017 at 08:21, Heyi Guo <[email protected]> wrote:
PCIe on some ARM platforms requires address translation, not only for
legacy IO access, but also for 32bit memory BAR access as well. There
will be "Address Translation Unit" or something similar in PCI host
bridges to translation CPU address to PCI address and vice versa. So
we think it may be useful to add address translation support to the
generic PCI host bridge driver.
I agree. While unusual on a PC, it is quite common on other
architectures to have more complex non 1:1 topologies, which currently
require a forked PciHostBridgeDxe driver with local changes applied.
This RFC only contains one minor change to the definition of
PciHostBridgeLib, and there certainly will be a lot of other changes
to make it work, including:
1. Use CPU address for GCD space add and allocate operations, instead
of PCI address; also IO space will be changed to memory space if
translation exists.
For I/O space, the translation should simply be applied to the I/O
range. I don't think it makes sense to use memory space here, given
that it is specific to architectures that lack native port I/O.
I made an assumption here that platforms supporting real port IO space
do not need address translation, like IA32 and X64, and port IO
translation implies the platform does not support real port IO space.
This may be a reasonable assumption. But I still think it is better
not to encode any assumptions in the first place.
Indeed the assumption is not so "generic", so I'll agree if you
recommend to support IO to IO translation as well. But I still hope to
have IO to memory translation support in PCI host bridge driver,
rather than in CPU IO protocol, since the faked IO space might only be
used for PCI host bridge and we may have overlapping IO ranges for
each host bridge, which is compatible with PCIe specification and PCIe
ACPI description.
That is fine. Under UEFI, these will translate to non-overlapping I/O
spaces in the CPU's view. Under the OS, this could be totally
different.
I fully agree with the PciRootBridgeLib interface change to support
MMIO offset. I guess that you will propose to add a
AddrTranslationOffset to PCI_ROOT_BRIDGE structure.
But I don't quite understand the needs of IO offset support.
And further more, there was a discussion in the mailing list
regarding how to utilize the Offset. There was 2 points
about the meaning of Offset and we cannot agree with each
other. Spec is not quite clear.
1. Offset = Host - Device
2. Offset = Device - Host
For example,
RC0 IO 0x0000 .. 0xffff -> CPU 0x00000 .. 0x0ffff
RC1 IO 0x0000 .. 0xffff -> CPU 0x10000 .. 0x1ffff
This is very similar to how MMIO translation works, and makes I/O
devices behind the host bridges uniquely addressable for drivers.
For our understanding, could you share the host bridge configuration
that you are targetting?
Thanks,
Ard.
How about adding a flag to indicate whether port IO is translated to
real port IO space or system memory space?
Thanks and regards,
Heyi
2. RootBridgeIoMemRead/Write, RootBridgeIoRead/Write need to get
translation of the corresponding aperture, add the translation to the
input address, and then call CpuIo2 protocol; IO access will also be
converted to memory access if IO translation exists.
Again, why is this necessary? A host bridge that implements a non 1:1
translation for port I/O ranges may be part of a system that has
native port I/O, and so the translation should be based on that.
3. RootBridgeIoConfiguration needs to fill AddrTranslationOffset in
the discriptor.
Indeed. Note that this has been a source of much confusion lately,
should we should discuss this carefully before spending time on an
implementation.
If it makes sense, then I'll continue to prepare the formal patch.
Any comments?
Thanks,
Gary (Heyi Guo)
Cc: Star Zeng <[email protected]>
Cc: Eric Dong <[email protected]>
Cc: Ruiyu Ni <[email protected]>
Cc: Ard Biesheuvel <[email protected]>
Cc: Jason Zhang <[email protected]>
---
MdeModulePkg/Include/Library/PciHostBridgeLib.h | 1 +
1 file changed, 1 insertion(+)
diff --git a/MdeModulePkg/Include/Library/PciHostBridgeLib.h
b/MdeModulePkg/Include/Library/PciHostBridgeLib.h
index d42e9ec..b9e8c0f 100644
--- a/MdeModulePkg/Include/Library/PciHostBridgeLib.h
+++ b/MdeModulePkg/Include/Library/PciHostBridgeLib.h
@@ -22,6 +22,7 @@
typedef struct {
UINT64 Base;
UINT64 Limit;
+ UINT64 Translation;
} PCI_ROOT_BRIDGE_APERTURE;
typedef struct {
--
2.7.4
--
Thanks,
Ray
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