On Fri, Apr 16, 2021 at 11:00:39AM +0200, Thomas Zimmermann wrote: > This patchset adds support for simple-framebuffer platform devices and > a handover mechanism for native drivers to take-over control of the > hardware. > > The new driver, called simpledrm, binds to a simple-frambuffer platform > device. The kernel's boot code creates such devices for firmware-provided > framebuffers, such as EFI-GOP or VESA. Typically the BIOS, UEFI or boot > loader sets up the framebuffers. Description via device tree is also an > option. > > Simpledrm is small enough to be linked into the kernel. The driver's main > purpose is to provide graphical output during the early phases of the boot > process, before the native DRM drivers are available. Native drivers are > typically loaded from an initrd ram disk. Occationally simpledrm can also > serve as interim solution on graphics hardware without native DRM driver. > > So far distributions rely on fbdev drivers, such as efifb, vesafb or > simplefb, for early-boot graphical output. However fbdev is deprecated and > the drivers do not provide DRM interfaces for modern userspace. > > Patches 1 and 2 prepare the DRM format helpers for simpledrm. > > Patches 4 to 8 add the simpledrm driver. It's build on simple DRM helpers > and SHMEM. It supports 16-bit, 24-bit and 32-bit RGB framebuffers. During > pageflips, SHMEM buffers are copied into the framebuffer memory, similar > to cirrus or mgag200. The code in patches 7 and 8 handles clocks and > regulators. It's based on the simplefb drivers, but has been modified for > DRM. > > Patches 3 and 9 add a hand-over mechanism. Simpledrm acquires it's > framebuffer's I/O-memory range and can be hot-unplugged by a native driver. > The native driver will remove simpledrm before taking over the hardware. > The removal is integrated into existing helpers, so existing drivers use > it automatically. > > I've also been working on fastboot support (i.e., flicker-free booting). > This requires state-readout from simpledrm via generic interfaces, as > outlined in [1]. I do have some prototype code, but it will take a while > to get this ready. Simpledrm will then support it. > > I've tested simpledrm with x86 EFI and VESA framebuffers, which both work > reliably. The fbdev console and Weston work automatically. Xorg requires > manual configuration of the device. Xorgs current modesetting driver does > not work with both, platform and PCI device, for the same physical > hardware. Once configured, X11 works. I looked into X11, but couldn't see > an easy way of fixing the problem. With the push towards Wayland+Xwayland > I expect the problem to become a non-issue soon. Additional testing has > been reported at [2]. > > One cosmetical issue is that simpledrm's device file is card0 and the > native driver's device file is card1. After simpledrm has been kicked out, > only card1 is left. This does not seem to be a practical problem however. Provided that patches 4 to 8 are squashed when merged: Acked-by: Maxime Ripard <maxime@xxxxxxxxxx> Maxime
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