Re: [PATCH] PXA255 LCD Driver

On Sat, Mar 20, 2004 at 12:01:03AM +0000, James Simmons wrote:

We can have it so that we can pass in a monitor string that can be used to 
select the proper LCD panel in the database. How does that sound?

That's still a little problematical because some hardware people put
a CPLD between the LCD controller and the LCD panel itself which
may change the characteristics.

It's fairly common to have one LCD controller appear in many different
devices (because its part of the CPU) and have the same display, yet
need different timing.

For example, see sa1100fb.c:

static struct sa1100fb_mach_info lq039q2ds54_info __initdata = {
        .pixclock       = 171521,       .bpp            = 16,
        .xres           = 320,          .yres           = 240,

        .hsync_len      = 5,            .vsync_len      = 1,
        .left_margin    = 61,           .upper_margin   = 3,
        .right_margin   = 9,            .lower_margin   = 0,

        .sync           = FB_SYNC_HOR_HIGH_ACT | FB_SYNC_VERT_HIGH_ACT,

        .lccr0          = LCCR0_Color | LCCR0_Sngl | LCCR0_Act,
        .lccr3          = LCCR3_OutEnH | LCCR3_PixRsEdg | LCCR3_ACBsDiv(2),
};

static struct sa1100fb_mach_info h3600_info __initdata = {
        .pixclock       = 174757,       .bpp            = 16,
        .xres           = 320,          .yres           = 240,

        .hsync_len      = 3,            .vsync_len      = 3,
        .left_margin    = 12,           .upper_margin   = 10,
        .right_margin   = 17,           .lower_margin   = 1,

        .cmap_static    = 1,

        .lccr0          = LCCR0_Color | LCCR0_Sngl | LCCR0_Act,
        .lccr3          = LCCR3_OutEnH | LCCR3_PixRsEdg | LCCR3_ACBsDiv(2),
};

Both of these are the same LCD panel (type LQ039Q2DS54) yet there are
two different sets of timing information, including the polarity of
the line and field clocks (which are equivalent to hsync and vsync.)

Also note that such panels are generally fixed resolution, though there
are a few rare exceptions where changing the colour depth is permitted.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core


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On Sat, 2004-03-20 at 09:06, Russell King wrote:

It's fairly common to have one LCD controller appear in many different
devices (because its part of the CPU) and have the same display, yet
need different timing.

This was something that I was worried about -- it seems like this sort
of thing would negate any benefit from building a database of panels for
general use.

Perhaps it would be posible to build a database of panels as described
in their datasheets. Boards which have a CPLD could perhaps define a
per-board fixup function, since they know the sync lines are inverted or
whatever.

I'm not sure though -- my experience is with our board which has a
PXA255 and no CPLD messing with the display controller stuff. I'm wary
of coming up with a solution which is only useful to me and noone
else...

Ian.
-- 
Ian Campbell, Senior Design Engineer
                                        Web: http://www.arcom.com
Arcom, Clifton Road,                    Direct: +44 (0)1223 403 465
Cambridge CB1 7EA, United Kingdom       Phone:  +44 (0)1223 411 200




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