Re: PCI-ISA Bridge not operating

[Jordan Crouse <jordan.crouse@amd.com>]

On 11/07/08 16:14 -0400, David Brigada wrote:
> Jordan Crouse wrote:
> > On 11/07/08 14:58 -0400, David Brigada wrote:
> >> David Brigada wrote:
> >>> Jordan Crouse wrote:
> >>>> On 11/07/08 10:58 -0400, David Brigada wrote:
> >>>>> Hi,
> >>>>>
> >>>>> I'm working with the MSM800XEV board from Digital-Logic.  This board 
> >>>>> uses a Geode LX800 for a CPU and has the CS5536 companion board also 
> >>>>> installed.  The board works with an IT8888G IC that provides a PCI/ISA 
> >>>>> bridge to a PC/104 bus that is externally provided.
> >>>>>
> >>>>> If I boot with FreeDOS, I can twiddle I/O ports, and the proper ISA 
> >>>>> signaling comes over the PC/104 bus.  In Linux, the /IOW or /IOR line 
> >>>>> goes low as expected, but the address doesn't come over the bus.  The 
> >>>>> DOS that I'm running doesn't seem to have any specific drivers for the 
> >>>>> chip, I'm guessing that the hardware should "just work" --- the IT8888G 
> >>>>> is designed to grab I/O requests in the ISA range off the PCI bus after 
> >>>>> a short delay if nothing else grabs them first.
> >>>>>
> >>>>> I have a feeling that it has something to do with the CS5536 companion 
> >>>>> chip, as it seems as though there is a driver for a PCI/ISA bridge on 
> >>>>> that chip, though I can't get much detail from AMD's datasheet on that 
> >>>>> functionality.  I do know that on the MSM800XEV, any such functionality 
> >>>>> is wired to the IT8888G, not the CS5536.
> >>>>>
> >>>>> There are two kernel config options related to the PCI IDs of the parts 
> >>>>> of the device that handle the ISA bus, CONFIG_SCx200_ACB and 
> >>>>> CONFIG_CS5535_GPIO.  I've tried disabling both, but it doesn't seem to help.
> >>>>>
> >>>>> In lspci, the CS5536 PCI/ISA bridge is shown, but not the IT8888G.
> >>>>>
> >>>>> Any ideas?
> >>>> ISA should indeed "just work".  The only thing I'm wondering is if
> >>>> the kernel is interfering (it shouldn't).  I assume that since it works
> >>>> in FreeDOS that there is no possibility that something on the PCI bus
> >>>> is grabbing the cycles instead.
> >>> That's what I'm thinking --- that the CS5536 PCI/ISA bridge is claiming 
> >>> the cycles.
> >>>
> >>>> How are you trying to access the device in Linux?  Through a kernel module
> >>>> or a user application running as root?
> >>> I've tried both.  I have a kernel module that I wrote for the hardware. 
> >>>   When I couldn't get that working, I tried looping some code that keeps 
> >>> touching the same I/O port that I'm using.
> >>>
> >>>> Jordan
> >>>>
> >>> Dave
> >> Looking through the documentation for the CS5536, in the "CS56536 
> >> Companion Device Data Book," section 5.2.8, it says the following:
> >>
> >>  > If the SDOFF (Subtractive Decode Off) bit in the GLPCI_MSR_CTRL (MSR
> >>  > 51000010h[10]) is cleared (reset value), any PCI transaction, other
> >>  > than Configuration Read/Write, Interrupt Acknowledge, and Special
> >>  > Cycle transactions, not claimed by any device (i.3., not asserting
> >>  > DEVSEL#) within the default active decode cycles (three cycles
> >>  > immediately after FRAME# being asserted) will be accepted by GLPCI_SB
> >>  > at the fourth clock edge.
> >>
> >> This is the same behavior that the IT8888G chip uses --- it waits three 
> >> cycles for another device to claim it and then passes the transaction 
> >> along.  I'm guessing that the CS5536 might be grabbing it (maybe it's 
> >> electrically closer, or the logic is more optimized) before the IT8888G 
> >> can handle it.
> >>
> >> Does this seem feasible as to what could be happening?
> > 
> > Sure, but then why does FreeDOS work?  It shouldn't be any different
> > when the bits hit the line.
> > 
> > Jordan
> 
> That *is* puzzling.  When I do lspci, the entry for the IT8888G does not 
> appear.  I don't have much experience with PCI internals.  Would that be 
> because there is no driver for it in the kernel, or is there something 
> more insidious afoot?

Well - the first step would be to get a dmesg output.  if the kernel
is doing anything to the device at all, the dmesg will show it.

Jordan

-- 
Jordan Crouse
Systems Software Development Engineer 
Advanced Micro Devices, Inc.