Re: [parisc-linux] Linux syscall ABI

[Frank Rowand <frank_rowand@mvista.com>]

Philipp Rumpf wrote:
> 
> > Drivers don't map anything. The assumption for GSC/PCI drivers is the
> > address given will work with readl/writel (or inb/outb) routines.
> 
> PCI drivers call ioremap(), which is free to do the mapping (but I don't
> think it should, for PA-RISC).
> 
> > For GSC, the HPA is in the struct hp_device->hpa field and readl/writel
> > are aliases for gsc_readl/gsc_writel.
> 
> which itself will be aliased to simple volatile accesses soon.
> 
> > gsc_readl/writel take a physical address as the address parameter.
> > I would like to get away from gsc_read for one simple reason: HPMC.
> > If a driver incorrectly accesses something which isn't supposed to
> > we get either an HPMC or undefined behavior. Most likely the HPMC.
> > If the read/write routines referenced a virtual address, we have
> > much better chances of getting a data page fault and some decent
> > debugging information to track down the problem.
> 
> HPMC is good debugging information - you've got PIM.  Of course, we want
> an HPMC handler too, at some point.  The assembly part just tries to
> find out if the machine is still usable, and resets it if it's not.
> If it is, we'd like it to be treated as normal interruption, and then
> have a CPU-specific fault handler that reads the interesting registers
> and prints a nice message.
> 
>         Philipp Rumpf
> 
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An HPMC may be delayed, relative to the instruction that caused it.  The worst
case is that a context switch _could_ occur before the HPMC occurs (and yes,
we did see this problem with our HP-UX and HP-RT VME systems when a VME
time-out was long enough).  This can make it more difficult to figure out what
instruction was issued to cause the HPMC. The advantage of the page fault is
that you know exactly what instruction caused the fault.

-Frank
-- 
MontaVista Software, Inc
frank_rowand@mvista.com