[PATCH v5 4/7] libweston: fbdev: set fb device info upon the first run.

[Pekka Paalanen]

On Fri, 29 Dec 2017 13:31:50 -0500
nerdopolis <bluescreen_avenger at verizon.net> wrote:

> This attempts to wake up secondary framebuffer devices
> (/dev/fb1 and up) as usually these devices start powered off, and
> the FBIOPUT_VSCREENINFO ioctl turns it on. This was tested on a
> qemu system with the options:
> 
> -vga none -device VGA,id=video0 -device secondary-vga,id=video1 \
> -device secondary-vga,id=video2
> ---
>  libweston/compositor-fbdev.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/libweston/compositor-fbdev.c b/libweston/compositor-fbdev.c
> index ef571339..39668aa8 100644
> --- a/libweston/compositor-fbdev.c
> +++ b/libweston/compositor-fbdev.c
> @@ -361,6 +361,13 @@ fbdev_frame_buffer_open(const char *fb_dev,
>  		return -1;
>  	}
>  
> +	/* Attempt to correct the framebuffer settings */
> +	if (fbdev_set_screen_info(fd, screen_info) < 0) {
> +		weston_log("Failed to set mode settings. "
> +		           "Attempting to open output anyway.\n");
> +	}
> +
> +
>  	return fd;
>  }
>  

Hi,

I think the existing code is a trap. fbdev_query_screen_info() asks the
fbdev what format it has, and then computes a Pixman format code from
it, which the renderer will then use. But, fbdev_set_screen_info() has
a hardcoded pixel format it tries to set.

If the original format on the fbdev is not the hardcoded format in
fbdev_set_screen_info(), and fbdev_set_screen_info() actually succeeds,
then the rendered format is wrong.

I believe that all DRM drivers providing fbdev via the shared fbdev
emulation always use the one format that matches the hardcoded one in
fbdev_set_screen_info(), and we get lucky. If someone tried this on a
"normal" fb driver, I think there is a chance to go wrong.

Do we care? I don't. Therefore:

Reviewed-by: Pekka Paalanen <pekka.paalanen at collabora.co.uk>


Thanks,
pq
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