On Thu, Aug 28, 2014 at 10:05 PM, Alexandre Courbot [off-list ref] wrote:

On Thu, Aug 28, 2014 at 7:00 PM, jonsmirl@gmail.com [off-list ref] wrote:

quoted

On Thu, Aug 28, 2014 at 9:54 PM, Alexandre Courbot [off-list ref] wrote:

quoted

On Thu, Aug 28, 2014 at 6:40 PM, jonsmirl@gmail.com [off-list ref] wrote:

quoted

On Thu, Aug 28, 2014 at 9:36 PM, Alexandre Courbot [off-list ref] wrote:

quoted

On Thu, Aug 28, 2014 at 12:19 PM, jonsmirl@gmail.com [off-list ref] wrote:

quoted

Is there some existing way to do early printk type output to a
framebuffer that has been set up by the bootloader?  early printk is
before any device drivers are loaded.

If not, what would it take to create a way to do this? Something along
the lines of build in the fbdev library and give it an address plus
x/y layout of the buffer. Assume that everything else is set up and
anything written to the buffer will appear on the display. Then hook
into where the kernel does early printk on uarts and add in support
for this buffer. The core fbdev library implements scrolling and
graphical characters.

simplefb does something like this (implement a console on top of a
framebuffer set up by the bootloader), but I don't think you can use
it for earlyprintk. It would be a very interesting option though (and

simplefb is a device driver so it doesn't process the early output.
This would need to be some custom code that gets the framebuffer
address  and x/y setup very early in the boot process. I'm fairly sure
nothing like it current exists.

You're right AFAICT. And although simplefb shares part of of idea it
also doesn't operate at the required level. Also contrary to what I
said it also does not implement a console, but just a framebuffer
device on top of which you need some more logic before you can think
about displaying strings.

turn on fbconsole support and it should work.

Yeah, but my point was, that I don't think you can use fbconsole that
early in the kernel?

You can't. But all of the needed code is sitting there in fbconsole.
There is just a small bit missing to make an early console work.
Mainly just the bit about address of buffer and x/y layout.


-- 
Jon Smirl
jonsmirl@gmail.com