mmap on /dev/fd0 on pc686 BSP not working at all.

[Vijay Kumar Banerjee]

Hello Karel, Gedare

Reading the post by Pavel in the other thread, I think the pc386
shouldn't be using the libbsd framebuffer. To be able to use the
driver in pc386, you'll have to disable the drivers from
rtems-littevgl. Please use `--no-drivers` option with ./waf configure
in rtems-littlevgl and remove the "fbdev_init" from the hello app. The
initialization of the fb is supposed to be handled by the drivers in
the BSP.

Best regards,
Vijay

On Mon, Sep 21, 2020 at 9:47 PM Gedare Bloom <gedare at rtems.org> wrote:
>
> Hi Karel,
>
> I don't know if I can provide any answers, but I can provide some
> guidance maybe. I implemented mmap() in rtems to provide portability
> and compliance for mmap applications that use MAP_SHARED with fixed
> addresses. We don't do any real mapping or translating of memory since
> there is no virtual memory support in rtems. Kevin Kirsepl
> extended/fixed the file handler part of that implementation
>
> There is an mmap helper implemented in libbsd: rtems-libbsd.git:
> /rtemsbsd/sys/fs/devfs/devfs_devs.c:391 devfs_imfs_mmap()
> Vijay implemented that as part of the BBB framebuffer work. I haven't
> studied it closely enough to give any advice on how to replicate/use
> that in another FB. Hopefully he may be able to chime in, as he also
> did a lot of the work with lvgl porting.
>
> The pc386 FB was written by one of Pavel Pisa's students, Jan Dolezal.
> I had hopes we could generalize the code to other targets because it
> is relatively simple compared to other framebuffers. I think someone
> tried with raspberry pi. But that effort hasn't really moved in a few
> years.
>
> My guess is that the pc386 fb needs to have something like devfs_imfs_mmap().
>
> Gedare
>
> On Sun, Sep 20, 2020 at 2:43 PM Karel Gardas <karel.gardas at centrum.cz> wrote:
> >
> >
> > Hello,
> >
> > I'm attempting to get rtems-example/lvgl/hello working on pc686 BSP. I'm
> > using VESA framebuffer which is default on pc686, although I needed to
> > do few fixes here and there to ensure littlevgl library compiles well.
> > All patches here
> > https://lists.rtems.org/pipermail/devel/2020-September/062186.html
> >
> > Now, everthing is compiled and VESA fb is well initialized -- or seems
> > so. Now, vgl library tries to use that fb (/dev/fb0) and basically tries
> > to mmap it for its own use. The code looks:
> >
> > void fbdev_init(void)
> > {
> >     // Open the file for reading and writing
> >     fbfd = open(FBDEV_PATH, O_RDWR);
> >     if(fbfd == -1) {
> >         perror("Error: cannot open framebuffer device");
> >         return;
> >     }
> >     printf("The framebuffer device was opened successfully.\n");
> > [...]
> >     // Map the device to memory
> >     fbp = (char *)mmap(0, screensize, PROT_READ | PROT_WRITE,
> > MAP_SHARED, fbfd, 0);
> >     if((intptr_t)fbp == -1) {
> >         perror("Error: failed to map framebuffer device to memory");
> >         return;
> >     }
> >     memset(fbp, 0, screensize);
> >
> >     printf("The framebuffer device was mapped to memory successfully.\n");
> >
> >
> > The mmap above fails. Screensize is realistic and good looking number.
> >
> > While debugging this mmap I see it fails on the call to function on line
> > 280:
> >
> >     err = (*iop->pathinfo.handlers->mmap_h)(
> >         iop, &mapping->addr, len, prot, off );
> >
> > it returns -1 and hence mmap failure since code below looks:
> >
> >     if ( err != 0 ) {
> >       mmap_mappings_lock_release( );
> >       free( mapping );
> >       return MAP_FAILED;
> >     }
> >
> > when I try to step into the problematic function above, I end up  in
> > default_mmap.c:31 on:
> >
> > rtems_set_errno_and_return_minus_one( ENOTSUP );
> >
> > and as the function claims it really returns -1 to me.
> >
> > Now, my obvious question is: how to make VESA fb mmappable? It looks
> > like the same library is working fine on BBB while using FreeBSD BBB
> > framebuffer driver, so there is probably some way how to convince RTEMS
> > mmap to work with fb0.
> >
> > Any idea how to proceed with this is highly appreciated.
> >
> > Thanks,
> > Karel
> >
> >
> > _______________________________________________
> > users mailing list
> > users at rtems.org
> > http://lists.rtems.org/mailman/listinfo/users