[PATCH v5 1/3] ARM: mxs: add GPMI-NFC support for imx23/imx28

[Lothar Waßmann]

Uwe Kleine-König writes:
> On Fri, Jul 08, 2011 at 12:24:22PM +0200, Lothar Waßmann wrote:
> > Uwe Kleine-König writes:
> > > Hello Huang,
> > > 
> > > On Fri, Jul 08, 2011 at 05:27:11PM +0800, Huang Shijie wrote:
> > > > >>>>The init function is used only to set up iomux, so the logical replacement is
> > > > >>>>a pointer to the iomux data, and calling mxs_iomux_setup_multiple_pads
> > > > >>>>directly from the driver.
> > > > >>>Why not put the iomux stuff into the per-machine table and get rid of
> > > > >>>the init callback, too?
> > > > >>The mmc (ssp) has pin conflict with gpmi on both mx23evk and mx28evk.
> > > > >>So, it's better to initialize the pin when the driver(GPMI or MMC)
> > > > >>is enabled.
> > > > >What do you do to prevent userspace from trying to use both devices?
> > > > The board can not support the two devices at the same time.
> > > > So the user can only use one device with the board.
> > > > 
> > > > >I guess you need to configure the hardware somehow to switch between the
> > > > >two using a jumper? Isn't it possible to detect the hardware setting and
> > > > >setup the muxer accordingly?
> > > > >
> > > > >IMHO an per-device init-callback is the wrong approach to solve a pin
> > > > >conflict.
> > > > Do you have any good solution about this?
> > > Put the pinmux corresponding to the one device that currently works in
> > > the pinmux list!?
> > > 
> > #define 'that currently works'
> > 
> > For a dedicated system that may not be a problem. But for development
> > kits and modular systems that allow peripheral modules to be plugged
> > in there is no 'one device that currently works'.
> Yeah, I know that problem. Back when I worked for a company selling
> development boards I solved it with clks. Not pretty but more convenient
> than kernel parameters or #ifdefs.
> The upside of doing it with clks is that if $customer tries to use both
> conflicting devices you get an error message instead of breaking device1
> when device2 is opened/probed.
>
This could be prevented by a reservation mechanism for the iomux like
for GPIOs.


Lothar Waßmann
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