Re: Proposal on WSDISPLAYIO damage reporting IOCTL

Hello,

On Tue, 13 May 2025 08:04:31 -0400 (EDT)
Mouse <[email protected]> wrote:

> > While implementing X11 userspace support for viogpu, I identified a
> > need for a unified WSDISPLAYIO mechanism to report framebuffer damage
> > areas to drivers.  [...]  
> 
> This design bothers me a little.  It feels to me like a shadow
> framebuffer with a push mechanism - with the shadow moved into the
> kernel.  This then leads me to ask: why is the shadow in the kernel
> instead of being in userland?

No, the shadow is in userland, the update is done by the kernel.
This is useful for:
- hardware where we don't have direct access to the framebuffer, or
  where access is prohibitively slow so it needs to be bundled into
  fewer, larger updates. Like USB graphics devices.
- virtualized hardware, where the visible framebuffer may well be a
  window on the host, outside the VM's address space. If we tell the
  hypervisor what we changed it needs fewer, smaller updates.

have fun
Michael