On 08/04/2019 14:47, Guenter Roeck wrote:
FC patch 1/4 ("resource: Request IO port regions from children
of ioport_resource").
Maybe I'm missing something, but on x86, drivers like f71882fg do not
crash the system because inb() *never* causes a crash.
If you want to build that driver for ARM, I think you need to make
sure that inb() on ARM also *never* causes a crash. I don't think
changing f71882fg and all the similar drivers is the right answer.
Agreed. As I had mentioned earlier, the driver changes are orthogonal:
the drivers should request the IO region before accessing it, primarily
to avoid conflicting accesses by multiple drivers in parallel. For
example, the f71882fg driver supports chips which implement hardware
monitoring as well as watchdog functionality, and both the hwmon
and the watchdog driver may try to access the io space.
If and how the system ensures that the IO region exists and/or that
inb() always succeeds is a different question. I would prefer a less
complex solution than the one suggested here, but that is my personal
opionion.
Hi Guenter,
I have a question about these super-IO accesses:
To me, it's not good that these hwmon, watchdog, gpio, etc drivers
make unconstrained accesses to 0x2e and 0x4e ports (ignoring the
request_muxed_region() call).
The issue I see is that on an arm, IO space for some other device may
be mapped in this region, so it would not be right for these drivers
to access those same regions.
Yes, but then there _could_ be some arm or arm64 device supporting one
of those chips,
so we can not just add something like "depends on !(ARM || ARM64)".
This looks like what has been added for PPC in commmit 746cdfbf01c0.
However, agreed, it's not a good approach.
Is there any other platform check which can be made to ensure that
accesses these super-IO ports is appropriate?
Not that I know of. It would make some sense to provide API functions
for Super-IO accesses, but that would be a lot of work, and I guess
it isn't really valuable enough for anyone to pick up and do.
Normally, if you have such a system, the respective drivers should not be
built. After all, this isn't the only instance where drivers
unconditionally
access some io region, no matter if the underlying hardware exists or not.
The only real defense against that is to not build those drivers into
a given kernel.
If we're going to support a multi-plaform kernel for a given arch, then
we can't always avoid it.
It seems that the only solution on the table now is to discard these IO
port accesses on arm64 when the IO port are not mapped.
Thanks again,
John
Guenter
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