Support VT switching for fbdev backend #89
Conversation
|
Specify which environments and hardware models have been validated with the proposed updates. |
These updates have been validated on Ubuntu 24.04 in a virtual machine. However, they cause a error on the Raspberry Pi 3B. I am currently investigating the issue. |
|
I will help reviewing the pull request this week. |
When I switch back and forth between tty2 and tty3, the Pi 3B would shut down. Pi.mp4 |
Raspberry Pi 4B requires power supply that can sustain at least 1.2A, and the recommended value is 3A, could you check for that? |
For my Raspberry Pi 3B, the recommended power supply is a 2.5A micro USB adapter. However, I am currently using a 1.5A micro USB adapter. |
|
This is the experimental result obtained on a Raspberry Pi 3B. Pi_3B.mp4 |
backend/linux_vt.h
Outdated
|
|
||
| static int *vt_fd; | ||
|
|
||
| static bool *is_vt_active; |
There was a problem hiding this comment.
What is is_vt_active used for?
There was a problem hiding this comment.
After setting is_vt_active, it can help twin_fbdev_work determine whether to proceed with screen rendering.
There was a problem hiding this comment.
After setting
is_vt_active, it can helptwin_fbdev_workdetermine whether to proceed with screen rendering.
Check the necessity.
There was a problem hiding this comment.
Without the is_vt_active flag, proper VT switching cannot be ensured. The primary reason for utilizing is_vt_active is the need to pass tx->vt_fd and tx->vt_active as parameters to the signal handler for configuration. However, achieving this directly is challenging. This discussion on passing multiple parameters to a signal handler using sigaction() suggests using global variables as a solution.
A similar scenario is discussed in Updating global variable in signal handlers, which provides valuable insights. It highlights that variables of type sig_atomic_t are guaranteed to be updated safely in signal handlers. Furthermore, it cautions against using locks in signal handlers, as they might be invoked while a lock is already held.
The code can be updated as follows:
static volatile sig_atomic_t *vt_fd;
static volatile sig_atomic_t *is_vt_actived;
The fbdev backend supports framebuffer rendering on a specifiend VT. To enhancce its compatibility in environments with multiple TTYs, the following improvements ensure that each framebuffer device operates independently on its own VT without affecting others. - Implement signal handlers to manage virtual terminal switching. - Pause screen rendering when switching to another VT. - Resume screen rendering when switching back to the original VT. The improvement has been validated on Ubuntu 24.04 running in a virtual machine and on a Raspberry Pi 3B.
|
Thank @huaxinliao for contributing! |
The fbdev backend supports framebuffer rendering on a specifiend VT. To enhancce its compatibility in environments with multiple TTYs, the following improvements ensure that each framebuffer device operates independently on its own VT without affecting others.