Re: [PATCH] fbdev: Distinguish between interlaced and progressive modes

[Fredrik Noring <noring@nocrew.org>]

Hi Bartlomiej,

> > With this change fb_find_mode can match interlaced and progressive
> > modes equally well, and distinguish between for example 1920x1080i
> > and 1920x1080p.
> > 
> > Signed-off-by: Fredrik Noring <noring@nocrew.org>
> 
> Could you please give some examples of use cases that need this change
> (i.e. which fbdev drivers need it for which modes etc.)?

I discovered the problem when developing a frame buffer driver for the
PlayStation 2 (not yet merged), using the following video modes for the
PlayStation 3 in drivers/video/fbdev/ps3fb.c:

    }, {
	/* 1080if */
	"1080if", 50, 1920, 1080, 13468, 148, 484, 36, 4, 88, 5,
	FB_SYNC_BROADCAST, FB_VMODE_INTERLACED
    }, {
	/* 1080pf */
	"1080pf", 50, 1920, 1080, 6734, 148, 484, 36, 4, 88, 5,
	FB_SYNC_BROADCAST, FB_VMODE_NONINTERLACED
    },

In ps3fb_probe, the mode_option module parameter is used with fb_find_mode
but it can only select the interlaced variant of 1920x1080 since the loop
matching the modes does not take the difference between interlaced and
progressive modes into account.

In short, without the patch, progressive 1920x1080 cannot be chosen as a
mode_option parameter since fb_find_mode (falsely) thinks interlace is a
perfect match.

Fredrik