[lm-sensors] modprobe of dme1737 on a ppc64 system results in kernel Oops

Jean Delvare khali at linux-fr.org
Fri Jul 22 22:23:49 CEST 2011

Hi Dean,

On Tue, 19 Jul 2011 20:12:55 -0500, Dean Nelson wrote:
> I was told that a modprobe of dme1737 on a ppc64 system running RHEL5
> would cause the kernel to Oops. And indeed it did. I found this was
> also the case on RHEL6, and the latest linux-3.0.
> It occurs when:
>    dme1737_init() calls
>    dme1737_isa_detect(0x2e, &addr) calls
>    dme1737_isa_sio_enter(sio_cip=0x2e) calls
>    outb(0x55, sio_cip=0x2e)
> And outb() goes through some macro transformations into out_8(),
> which does a store byte indexed assembly (stbx) instruction. Along
> the way the port number (0x2e) is changed into an address to
> which the value 0x55 is stored. The address is based on:
>    addr = pci_io_base + port      // on RHEL5
>    addr = _IO_BASE + port         // on RHEL6 and linux-3.0
> With RHEL5 on the system I was running, pci_io_base was set to
> 0xd000080000000000. And with RHEL6 and linux-3.0, _IO_BASE was also
> set to 0xd000080000000000.

Thanks for raising this problem, this is the first time I hear about it.

> There are other hwmon drivers that also Oops on a ppc64 system when
> modprobed. Some of them encounter the Oops when executing inb()/in_8().
> The following are the drivers that I confirmed oops and the args passed
> into in_8() or out_8().
>    drivers/hwmon/dme1737.ko    out_8(addr=0xd00008000000002e, val=0x55)
>    drivers/hwmon/f71805f.ko    out_8(addr=0xd00008000000002e, val=0x87)
>    drivers/hwmon/lm78.ko        in_8(addr=0xd000080000000291)
>    drivers/hwmon/pc87427.ko    out_8(addr=0xd00008000000002e, val=0x20)
>    drivers/hwmon/vt1211.ko     out_8(addr=0xd00008000000002e, val=0x87)

Of these, lm78 is different, the chip is an ISA device, when all other
drivers are for more recent LPC (Super-I/O) devices. It should be fixed
in a similar way as the w83781d driver was fixed: putting the
problematic code inside #ifdef CONFIG_ISA/#endif.

> It's been reported that there are a number of other hwmon drivers that
> exhibit the same behavior, but I've not confirmed that.

Indeed, f71882fg, it87, pc87360, sis5595, smsc47b397, smsc47m1,
w83627ehf and w83627hf certainly have the same problem.

> All three kernels have an isa_io_base variable and where it is
> defined in the code is a comment that says: /* NULL if no ISA bus */.
> (In RHEL5, defined in arch/powerpc/kernel/pci_64.c; and in RHEL6 and
> linux-3.0, it's in arch/powerpc/kernel/isa-bridge.c.) On the system
> I was running on it was always NULL.
> So how should this issue be resolved? I can think of three
> directions one could head in:
>    . Don't build these drivers for systems that don't have an ISA bus.

Works for lm78, not for other drivers which don't depend on the ISA bus
(x86_64 has no ISA bus but needs these drivers.)

For the other drivers, I think we should simply not build them on
PPC64, as I don't think they are needed there at all. In fact I am
unsure if any of the affected driver is needed on an architecture not
x86 or x86_64.

>    . Make a check for an ISA address and no ISA bus reside in the
>      callers to outb()/inb()

Are there any other drivers doing this?

>    . Make such a check reside in outb()/inb().

This would be very, very expensive at run-time, so I don't think it is
an option at all.

> I tried adding 'ISA' to the 'depends on' lines for the above
> drivers in drivers/hwmon/Kconfig. That worked for the ppc64 system
> I was running on, but I don't know if it's really a valid approach.
> The various CONFIGs (e.g., 'ISA_DMA_API') and the setting of such on
> the various architectures is something that is a mystery to me. But if
> there was something that could be used (like 'ISA'), the first option
> above would seem to be the simplest one to take.

ISA can't be used for the reason given above, and I am unfortunately
not aware of any other option that could be used instead.

> The third option, might look something like...
> For CONFIG_PPC64 on RHEL6 and linux-3.0, I found in the following
> function arch/powerpc/include/asm/pci-bridge.h:
> static inline int isa_vaddr_is_ioport(void __iomem *address)
> {
>          /* Check if address hits the reserved legacy IO range */
>          unsigned long ea = (unsigned long)address;
>          return ea >= ISA_IO_BASE && ea < ISA_IO_END;
> }
> And when I was running on these kernels I found,
>    ISA_IO_BASE = 0xd000080000000000
>    ISA_IO_END  = 0xd000080000010000
> So perhaps DEF_MMIO_OUT_BE(), which is what produces out_8() and is
> found in arch/powerpc/include/asm/io.h, could be changed to something
> like:
> #define DEF_MMIO_OUT_BE(name, size, insn)                               \
> static inline void name(volatile u##size __iomem *addr, u##size val)    \
> {                                                                       \
>         if (!isa_vaddr_is_ioport(addr) || isa_io_base) {                 \
>                  __asm__ __volatile__("sync;"#insn"%U0%X0 %1,%0"         \
>                          : "=m" (*addr) : "r" (val) : "memory");         \
>                  IO_SET_SYNC_FLAG();                                     \
>         }                                                                \
> }
> And the others, like DEF_MMIO_IN_BE(), in a similar way.

This sounds pretty complex, to solve a problem which isn't as far as I
can see.

> But I really must say that I know nothing about ppc systems. This was my
> first exposure to them. So the above might be pure nonsense. Besides, it
> doesn't begin to address the other architectures that might have issues
> with reading/writing ISA addresses when there is no ISA bus.
> So, again, how should this issue be resolved?

I know nothing about ppc either, but I'm sure we would know if these
systems needed these drivers. So the easy fix is to simply make all
offending drivers depend on !PPC. Or be even bolder and make them
depend on X86. I'm sure we'll know soon enough if any other
architecture is suddenly missing a driver they were using (IA64 maybe)
I'm fine both ways.

And for lm78 we want a specific fix, copied from w83781d (not sure why
this wasn't done already.) I'll do that, I can test this driver.

Jean Delvare

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