[PATCH 05/18] fbdev: initialize yoffset of varinfo

[Marc Chalain]

2013/6/21 David Herrmann <dh.herrmann at gmail.com>

> Hi
>
> On Fri, Jun 21, 2013 at 12:05 PM, Marc Chalain <marc.chalain at gmail.com>
> wrote:
> >
> >
> > 2013/6/21 David Herrmann <dh.herrmann at gmail.com>
> >>
> >> Hi
> >>
> >> On Fri, Jun 21, 2013 at 11:43 AM, Marc Chalain <marc.chalain at gmail.com>
> >> wrote:
> >> >
> >> > 2013/6/21 David Herrmann <dh.herrmann at gmail.com>
> >> >>
> >> >> Hi
> >> >>
> >> >> On Fri, Jun 21, 2013 at 10:49 AM, mchalain [marc.chalain at gmail.com]
> >> >> <marc.chalain at gmail.com> wrote:
> >> >> > From: mchalain <marc.chalain at gmail.com>
> >> >> >
> >> >> >  it initializes varinfo.yoffset. varinfo.yoffset has to
> >> >> >  point on the beginning of the video memory.
> >> >> >  The card uses this value to push on the screen a part of
> >> >> >  the video memory when this one is larger than the screen.
> >> >> >
> >> >> > ---
> >> >> >  weston/src/compositor-fbdev.c |    6 ++++++
> >> >> >  1 file changed, 6 insertions(+)
> >> >> >
> >> >> > diff --git a/weston/src/compositor-fbdev.c
> >> >> > b/weston/src/compositor-fbdev.c
> >> >> > index adfb67a..d2aee9b 100644
> >> >> > --- a/weston/src/compositor-fbdev.c
> >> >> > +++ b/weston/src/compositor-fbdev.c
> >> >> > @@ -368,6 +368,11 @@ fbdev_query_screen_info(struct fbdev_output
> >> >> > *output, int fd,
> >> >> >                 return -1;
> >> >> >         }
> >> >> >
> >> >> > +       if (varinfo.yoffset != 0) {
> >> >> > +               varinfo.yoffset = 0;
> >> >> > +               if (ioctl(fd, FBIOPAN_DISPLAY, &varinfo) < 0)
> >> >> > +                       return -1;
> >> >> > +       }
> >> >>
> >> >> Why do you need this? It's unnecessary. We call FBIOPUT_VSCREENINFO
> >> >> after fbdev_query_screen_info(), anyway. Furthermore, not all drivers
> >> >> support panning even though the yoffset may be non-zero (you need
> >> >> FBIOPUT_VSCREENINFO then).
> >> >>
> >> >> I think you can just drop this here but keep the yoffset=0 below.
> >> >>
> >> >
> >> > where do you use  FBIOPUT_VSCREENINFO ? I only find inside
> >> > fbdev_set_screen_info but this function is called only when the output
> >> > is
> >> > reenable not at the startup.
> >>
> >> My bad!
> >> But still, you now call FBIOPAN_DISPLAY on _every_
> >> fbdev_query_screen_info() while it is only needed during initial setup
> >> as VT_ENTER calls fbdev_set_screen_info(), anyway. So instead, I'd
> >> recommend to just call fbdev_set_screen_info() during initial setup as
> >> well.
> >>
> >
> > No I call  FBIOPAN_DISPLAY only at startup after yoffset is set to 0
>
> You call it everytime yoffset isn't 0. So if you VT_LEAVE, another
> application changes the yoffset for whatever reason and we VT_ENTER,
> you will end up calling FBIOPAN_DISPLAY again followed by
> fbdev_set_screen_info() if the screen-info changed.
>
> Don't expect applications on other VTs to behave as expected. They may
> do anything! They may even use some acceleration which we in weston
> aren't aware of.
>
> If another application set yoffset, with VT_ENTER we pass inside
fbdev_set_screen_info
and yoffset is set to 0.
After fbdev_set_screen_info is buggy and this patch is not a bugfix...
the bug is you set varinfo.bits_per_pixel with a value that could be
different of 32 and
after you set the colors as A8R8G8B8 ...
I don't want to use it, because I can't check all cases of this function,
my card is too simple...

>> > It seems strange that FBIOPAN_DISPLAY is not supported by some devices.
> >> > I
> >> > used this one to not set all the varinfo on the device and to be
> faster.
> >>
> >> See ./drivers/video/fbmem.c fb_pan_display(). Trivial fbdev drivers
> >> might not support it, but user-space can still set the offset via
> >> FBIOPUT_VSCREENINFO. If you want, you can call FBIOPAN_DISPLAY and if
> >> it fails, you use FBIOPUT_VSCREENINFO.
> >>
> > I read the yoffset hasn't to be null in  FB_VMODE_YWRAP . But yoffset is
> > only used for panning.
> > It's useless to set it if it doesn't use (fbmem.c uses yoffset only for
> > panning in your example too)
>
> A driver may not support FBIOPAN_DISPLAY but still support panning via
> FBIOPUT_VSCREENINFO. If any framebuffer parameter change requires a
> full modeset, there is no reason to support FBIOPAN_DISPLAY. But
> panning may still be supported via yoffset and FBIOPUT_VSCREENINFO.
>
> You tell that kernel bug must be corrected by kernel developers in the
thread about SYN_DROPPED
and now you tell me that we have to check that the driver should not be
completed ???
I don't understand the need to add useless code. I will change
FBIOPAN_DISPLAY by
FBIOPUT_VSCREENINFO but it's only to make you happy.

> Cheers
> David
>
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