[U-Boot] What's purpose of DEV_FLAGS_SYSTEM and DEV_EXT_VIDEO?

[Anatolij Gustschin <agust@denx.de>]

Hi Bin,

On Mon, 17 Aug 2015 13:09:20 +0800
Bin Meng <bmeng.cn@gmail.com> wrote:
...
> I plan to send a patch to remove the DEV_FLAGS_SYSTEM and
> DEV_EXT_VIDEO. They look useless to me. For example,
> 
> $ grep -nr DEV_FLAGS_SYSTEM *
...
> drivers/video/cfb_console.c:2296:       console_dev.flags =
> DEV_FLAGS_OUTPUT | DEV_FLAGS_SYSTEM;
> drivers/net/netconsole.c:325:   dev.flags = DEV_FLAGS_OUTPUT |
> DEV_FLAGS_INPUT | DEV_FLAGS_SYSTEM;
> include/stdio_dev.h:19:#define DEV_FLAGS_SYSTEM 0x80000000      /*
> Device is a system device            */
> 
> Except for this one below which tests the flag and prints an 'S',
> common/cmd_console.c:33:                        (dev->flags &
> DEV_FLAGS_SYSTEM) ? 'S' : '.',
> 
> I don't see any actual meaning of this flag. I wonder if someone on
> the mailing list knows the history.

This is very old code, and I do not know the history. Both flags could
be dropped, I've no objection.

> Also I noticed that several blackfin boards' video driver only set
> this flag without setting DEV_FLAGS_OUTPUT.
> 
> board/bf527-ezkit/video.c:442:  videodev.flags = DEV_FLAGS_SYSTEM;
>  /* No Output */
> board/cm-bf548/video.c:336:     videodev.flags = DEV_FLAGS_SYSTEM;
>  /* No Output */
> board/bf548-ezkit/video.c:332:  videodev.flags = DEV_FLAGS_SYSTEM;
>  /* No Output */
> board/bf533-stamp/video.c:168:  videodev.flags = DEV_FLAGS_SYSTEM;
> 
> I wonder these video drivers are not used for system output purpose?

No, they don't. In the board configs I see that these use very small
Displays (320x240). These shows the logo, but it would be very difficult
to use such displays as a console.

Thanks,

Anatolij