Re: [PATCH 4/8] minnowboard: Add base platform driver for the MinnowBoard

[Darren Hart <dvhart@linux.intel.com>]

On Thu, 2013-06-27 at 11:14 +0200, Linus Walleij wrote:
> On Wed, Jun 26, 2013 at 3:53 AM, Darren Hart <dvhart@linux.intel.com> wrote:
> 
> > Provide a minimal public interface:
> >         minnow_detect()
> >         minnow_lvds_detect()
> >         minnow_hwid()
> >         minnow_phy_reset()
> 
> So instead of these calling drivers issueing gpio_request() themselves
> to obtain a resource, they make a function call to this proxy that issue
> gpio_request() for them.
> 
> This is generally not how we do things. A driver should request its
> GPIO just as it requests its regulator or clock or IRQ line or anything
> else.

I'll fix this for minnow_phy_reset() by moving the reset routine into
the pch_gbe driver and have it request the GPIO, using the pci_id
structure to determine the GPIO line.

I'll drop minnow_lvds_detect() and work toward the firmware managing
this aspect instead.

minnow_detect() doesn't access GPIO.

minnow_hwid() just returns an int that the minnowboard platform driver
read from the GPIO. This seems like a proper abstraction to me. Do you
object to this one as well?

>  Centralizing resource handling is not a good idea IMO, it's better
> that each driver request it's GPIO pin(s) and do the stuff it needs
> with them.

Understood. Since minnow_hwid() is not currently used anywhere anyway,
I'll take Olof's advice and just drop it. We can always add it back if
it becomes necessary.

> This of course creates the problem of associating the GPIOs to a
> driver and how it should look that up, which I guess ACPI can do,
> isn't that what acpi_find_gpio() is for?

The only one that remains is pch_gbe and we have a PCI Subsystem ID
there that we can use. Once we determine it is a MinnowBoard, we can
look the GPIO up by chip and offset. If this changes in future board
revs, we'll need minnow_hwid(), or we'll have to figure something out
either in the PCI config space or via ACPI as you suggested.

Thanks Linus, appreciate all the feedback.

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