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

From: Huang Shijie <b32955@freescale.com>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: "Arnd Bergmann" <arnd@arndb.de>,
	s.hauer@pengutronix.de, w.sang@pengutronix.de,
	thierry.nolf.barco@gmail.com, linux-mtd@lists.infradead.org,
	"Shawn Guo" <shawn.guo@freescale.com>,
	shijie8@gmail.com, linux-arm-kernel@lists.infradead.org,
	"Lothar Waßmann" <LW@KARO-electronics.de>
Subject: Re: [PATCH v5 1/3] ARM: mxs: add GPMI-NFC support for imx23/imx28
Date: Mon, 11 Jul 2011 16:30:34 +0800	[thread overview]
Message-ID: <4E1AB4AA.7020702@freescale.com> (raw)
In-Reply-To: <20110711080003.GE13840@pengutronix.de>

Hi Uwe:
> 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
Could you give me some more details about how did you solve it with clks?

I am confused about it.

thanks

Best Regards
Huang Shijie
> 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.
> IMHO this last scenario must not happen, so I strongly object to setup
> the pinmuxing in an .init callback.
>
> Best regards
> Uwe
>