Re: gpio-sch GPIO_SYSFS access

From: Darren Hart
Date: Fri Feb 08 2013 - 12:44:19 EST

On 02/08/2013 03:07 AM, Samuel Ortiz wrote:
> On Fri, Feb 08, 2013 at 02:36:16AM -0800, Darren Hart wrote:
>> On 02/08/2013 12:49 AM, Samuel Ortiz wrote:
>>>> Well, this happens when the driver in question gets removed by another
>>>> driver.
>>> removed by another driver ? I'm not sure I understand what that means.
>> In my case, the gpio-sch probe function runs and creates the gpiochip
>> with 14 GPIO lines. Later lpc-sch probe runs,
> That's weird: The lpc-sch probe should run first. Then the gpio-sch probe
> should be called when lpc-sch adds the MFD cells as platform devices, from
> lpc_sch_probe().
> So someone is adding gpio-sch as a platform device, and that is wrong.
>> adds devices to the mfd
>> device list, fails the WDT base address as described below, and then
>> removes the devices in the mfd device list, which triggers the removal
>> of the gpio-sch device.
>> If I just skip the WDT lookup and not abort, then things work as I had
>> expected. Sooo... does it make sense to remove ALL the MFD device when
>> the read of the WDTBA registers indicates "Disabled"? Seems extreme to me.
> Yes, that's a bit rough. But I think you have a more fundamental problem where
> you're probing both LPC and your GPIO driver.
>>>> Samuel, does it make sense for CONFIG_GPIO_SCH to require
>>>> CONFIG_LPC_SCH? I'm building for a Queensbay (Atom E6xx + EG20T PCH).
>>>> There is no SCH as I understand things. Can these be decoupled?
>>> They actually don't have code dependency, GPIO_SCH selects LPC_SCH beacause
>>> the MFD parts actually creates the GPIO device.
>>> So you're saying Queensbay use the same GPIO IP block without actually having
>>> SCH ?
>> That is how I currently understand it. These drivers appear to have been
>> originaly written for the Silverthorne (Z5xx) CPUs and the Intel SCH
>> chipset.
> If your lpc_sch_probe routine runs, you basically have an LPC on your PCI bus
> here. As I said, PCI probes lpc_sch _and_ gpio_sch is probed as well (As a
> platform device, probably coming from your SFI tables or so). Probing both is
> problematic, especially since you do have an LPC sitting on your PCI bus.

Upon closer inspection what is really happening is the lpc_sch probe
runs and adds the sch_gpio device with the mfd_add_devices call which
creates the platform device. At that time the gpio_sch probe runs and
sets up the gpio stuff. Control returns to the lpc_sch which then tries
to find the WDT, fails, and removes all the mfd devices it had added

I'm working with firmware (UEFI, ACPI - not SFI) on why WDTBA is 0, but
in the meantime I'll work up a patch to not destroy all the valid devices
when that one fails.

Darren Hart
Intel Open Source Technology Center
Yocto Project - Technical Lead - Linux Kernel
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