colibri-pxa300: LCD_LDD / LCD_CS gpio conflict

[Eric Miao]

On Tue, Sep 7, 2010 at 5:15 PM, pieterg <pieterg at gmx.com> wrote:
> On Tuesday 07 September 2010 09:29:59 Eric Miao wrote:
>> On Tue, Sep 7, 2010 at 3:20 PM, pieterg <pieterg at gmx.com> wrote:
>> > On Tuesday 07 September 2010 04:43:31 Eric Miao wrote:
>> >> On Mon, Sep 6, 2010 at 9:12 PM, pieterg <pieterg at gmx.com> wrote:
>> >> > In colibri-pxa300.c, line 132, gpio config GPIO62_LCD_CS_N is
>> >> > overriding the GPIO62_LCD_LDD_8 configuration, earlier in the pin
>> >> > config table.
>> >> >
>> >> > As a result, one pixel data line is missing, obviously causing wrong
>> >> > pixel data on passive lcd panels.
>> >> >
>> >> > Not sure what the best workaround should be.
>> >> > LDD_CS is not available on the colibri evalboard as far as I can
>> >> > see, so we might just define GPIO127_LCD_CS_N instead? (till the
>> >> > soc/carrier board configs have been split)
>> >> >
>> >> > Or for now just put GPIO62_LCD_CS_N between
>> >> > #ifdef ?
>> >>
>> >> Possibly define two groups of LCD pin configurations and select them
>> >> when the appropriate LCD expansion card is plugged. If it can be
>> >> detected at run-time, that will be perfect, otherwise have to come
>> >> up with ugly #ifdef .. #else then.
>> >
>> > I don't think you can detect whether an active or passive lcd panel is
>> > used. And since the LCD_CS_N is only used for active panels, we can be
>> > sure that we only need it when CONFIG_FB_PXA_SMARTPANEL is defined.
>> > So though it's ugly, it is already there, and we can use it.
>>
>> CONFIG_FB_PXA_SMARTPANEL is an inclusive config option not
>> a mutual exclusive, so it's enabling a capability. Even if it's selected
>> the board code can still select parallel/smartpanel protocol in the
>> pxafb_mach_info.lcd_conn field. It just cannot be used safely here.
>
> OK, I didn't realise that. In that case we cannot use it.
>
>> If it's not run-time detectable, the ugliest way is to add a board
>> specific kernel command line option, though I'd shrug.
>
> I think a command line option is almost as ugly as a CONFIG define ;)
> How about using GPIO127_LCD_CS_N instead? Then at least we won't have a
> conflict with the LDD pins.
> I don't know why the conflicting GPIO62_LCD_CS_N was chosen in the first
> place?

That depends on hardware, it's not like whichever pin with functionality of
LCD_CS_N can be used. Need to check with schematics if the LCD_CS_N
signal is routed to GPIO62 or GPIO127.

>
> Rgds, Pieter
>