Hello, On Tue, 13 May 2025 08:04:31 -0400 (EDT) Mouse <mo...@rodents-montreal.org> 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
