On 11/3/2015 11:55 AM, Arnd Bergmann wrote:
On Tuesday 03 November 2015 11:33:18 Sinan Kaya wrote:
On 11/3/2015 10:59 AM, Arnd Bergmann wrote:
On Tuesday 03 November 2015 10:10:21 Sinan Kaya wrote:
I don't see anywhere in the SBSA spec addendum that the PCI
configuration space section that unaligned accesses *MUST* be supported.
If this is required, please have this info added to the spec. I can work
with the designers for the next chip.
Unaligned access on the current hardware returns incomplete values or
can cause bus faults. The behavior is undefined.
Unaligned accesses are not allowed, but any PCI compliant device must
support aligned 1, 2 or 4 byte accesses on its configuration space,
though the byte-enable mechanism. In an ECAM host bridge, those are
mapped to load/store accesses from the CPU with the respective width
and natural alignment.
As far as I see, the endpoints do not have any problems with unaligned
accesses. It is the host bridge itself (stuff that doesn't get on the
PCIe bus and uses traditional AXI kind bus internally) has problems with
alignment.
If Linux is expecting all HW vendors to implement alignment support,
this needs to be put in the SBSA spec as a hard requirement.
As I said, it's not unaligned accesses at all, just 1-byte and aligned
2-byte accesses, and it's not Linux mandating this but the PCI
spec. Please read Russell's email again, it is not possible for PCI
to work according to the specification unless the host bridge allows
sub-32-bit accesses.
I'll check back with the hardware designers. Seeing readb/readw/readl
made me nervous that we are trying unaligned access from any boundaries.
In any case, the hardware document says 32 bit configuration space
access to the host bridge only. I'll get more clarification.
You can probably work around this by using the legacy I/O port method
rather than ECAM, if the PCI host bridge itself is functional and just
the host bus it is connected to is buggy.
From the sounds of it, we'll need a quirk for config space. We support
legacy I/O only to make the endpoints happy. Some endpoints do not get
initialized if they don't have a BAR address assigned to all the BAR
resources.
I just saw David Daney's email. I like his idea. I think this chip will
fit into the same category.
Arnd
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Sinan Kaya
Qualcomm Technologies, Inc. on behalf of Qualcomm Innovation Center, Inc.
Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, a
Linux Foundation Collaborative Project
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