Hi, On 3/29/21 2:31 PM, Thomas Zimmermann wrote: > Hi > > Am 25.03.21 um 12:29 schrieb Hans de Goede: >> Hi, >> >> On 3/18/21 11:29 AM, 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 3 and 4 add a hand-over mechanism. Simpledrm acquires it's >>> framebuffer's I/O-memory range and provides a callback function to be >>> removed by a native driver. The native driver will remove simpledrm before >>> taking over the hardware. The removal is integrated into existing helpers, >>> so drivers use it automatically. >>> >>> Patches 5 to 10 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 8 and 9 handles clocks and >>> regulators. It's based on the simplefb drivers, but has been modified for >>> DRM. >> >> Thank you for your work on this, this is very interesting. >> >>> 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. >>> >>> TODO/IDEAS: >>> >>> * provide deferred takeover >> >> I'm not sure what you mean with this ? Currently deferred-takeover is >> handled in the fbcon code. Current flickerfree boot works like this >> (assuming a single LCD panel in a laptop): >> >> 1. EFI/GOP sets up the framebuffer, draws a vendor logo >> 2. The bootloader runs in silent mode and does not touch anything gfx related >> 3. kernel boots, with a loglevel of 3 so only CRIT/EMERG messages are shown >> 2. efifb loads; and tells fbcon that a framebuffer is now available for it to "bind" >> to. Since CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER=y fbcon defers taking over >> the console and leaves the dummy-console driver in place (unless there have already >> been kernel messages logged, which there shouldn't because loglevel=3) >> 3. i915 loads, reads out the hw state compares this to the preferred-mode for the >> panel which it would set, they match, nothing happens. i915 takes ownership >> of the scanout-buffer set up by the GOP, but leaves it in place. >> i915 also removes the efifb /dev/fb0 and installs its own /dev/fb0 fbdev compat >> device, fbcon is notified of this, but is still deferred and leaves the dummy >> console driver in place as console driver. >> 4. Plymouth loads, allocates a new scan-out buffer at the panel's preferred resolution, >> plymouth reads the vendor-logo through the BGRT ACPI interface and fills the >> scanout-buffer with the vendor-logo + a spinner. Then plymouth installs the new >> scanout-buffer on the crtc, this is done atomically during vsync, so the user >> sees no changes, other then the spinner appearing >> (note the active VT is now in graphical mode) >> 5. From here on not flickering is a userspace problem >> >> AFAICT this should work fine with simplekms too, unless it clears the screen >> to black when it binds. > > I forgot to add the code that clears the screen, but that's the case here. > > Instead of a plane-disable operation, simpledrm can at best clear the screen. This would happen during the initial mode-config reset IIRC. Hmm, clearing the screen without any (atomic) modesets being initiated by either an in kernel drm-client or userspace seems wrong, this is certainly different from what the i915 driver does. The way I see it either a drm client provides a new framebuffer in which case you copy that over the old contents, effectively clearing it. Or a drm-client gets a handle and draws to the current fb directly, in which case it is the clients responsibility to clear it itself first. IOW I believe that simpledrm should not clear the screen itself at all. Regards, Hans > But we need to keep the display content stored in a framebuffer, so read-out helpers are required. There are more users of these read-out helpers. Adding them at some point probably makes sense. > > Other drivers might also want to read the initial config from simpledrm via read-out helpers. I think only i915 currently supports something like that ATM. > > Best regards > Thomas > >> >> An addition to the above sequence, if at any time either the kernel or userspace >> prints a message to the console; and at that time a fbdev is registered then fbcon >> will takeover as the console driver from the dummy driver and it will start drawing >> to the registered fbdev (1), destroying the framebuffer contents. Also if any messages >> where printend while no fbdev was registered, then fbcon will takeover the console >> as soon as a fbdev gets registered. >> >> So since we already have deferred-takeover in the fbcon code, I wonder what you >> mean when you are talking about "provide deferred takeover" for simplekms? >> >> Regards, >> >> Hans >> >> >> 1) Except when the VT has been switched to GFX mode when this happens, then fbcon >> will delay using the fbdev until the VT is switched back to text mode. >> >> >> p.s. >> >> This has the interesting side effect then when logging into a desktop GUI session: >> kernel -> plymouth -> gdm -> GNOME user session >> >> There never is any output to the text-console and fbcon never takes-over, so on >> many Laptops running say Fedora workstation the fbcon code is actually unused >> until the user manually switches to another virtual-console to log in in >> text-mode: >> >> [hans@x1 ~]$ dmesg | grep -E 'fbcon|Console:|Truecolor' >> [ 0.258904] Console: colour dummy device 80x25 >> [ 1.274726] efifb: Truecolor: size=8:8:8:8, shift=24:16:8:0 >> [ 1.274768] fbcon: Deferring console take-over >> [ 2.540894] fbcon: i915drmfb (fb0) is primary device >> [ 2.540896] fbcon: Deferring console take-over >> [hans@x1 ~]$ uptime >> 12:29:39 up 4:19, 1 user, load average: 0.58, 0.75, 0.81 >> >> Look mom no fbcon >> >> >> >> >>> * provide bootsplash DRM client >>> * make simplekms usable with ARM-EFI fbs >>> >>> v2: >>> * rename to simpledrm, aperture helpers >>> * reorganized patches >>> * use hotplug helpers for removal (Daniel) >>> * added DT match tables (Rob) >>> * use shadow-plane helpers >>> * lots of minor cleanups >>> >>> [1] https://lore.kernel.org/dri-devel/CAKMK7uHtqHy_oz4W7F+hmp9iqp7W5Ra8CxPvJ=9BwmvfU-O0gg@xxxxxxxxxxxxxx/ >>> [2] https://lore.kernel.org/dri-devel/1761762.3HQLrFs1K7@nerdopolis/ >>> >>> Thomas Zimmermann (10): >>> drm/format-helper: Pass destination pitch to drm_fb_memcpy_dstclip() >>> drm/format-helper: Add blitter functions >>> drm/aperture: Move fbdev conflict helpers into drm_aperture.h >>> drm/aperture: Add infrastructure for aperture ownership >>> drm: Add simpledrm driver >>> drm/simpledrm: Add fbdev emulation >>> drm/simpledrm: Initialize framebuffer data from device-tree node >>> drm/simpledrm: Acquire clocks from DT device node >>> drm/simpledrm: Acquire regulators from DT device node >>> drm/simpledrm: Acquire memory aperture for framebuffer >>> >>> Documentation/gpu/drm-internals.rst | 12 + >>> MAINTAINERS | 7 + >>> drivers/gpu/drm/Kconfig | 7 + >>> drivers/gpu/drm/Makefile | 1 + >>> drivers/gpu/drm/drm_aperture.c | 287 ++++++++ >>> drivers/gpu/drm/drm_format_helper.c | 96 ++- >>> drivers/gpu/drm/mgag200/mgag200_mode.c | 2 +- >>> drivers/gpu/drm/tiny/Kconfig | 17 + >>> drivers/gpu/drm/tiny/Makefile | 1 + >>> drivers/gpu/drm/tiny/cirrus.c | 2 +- >>> drivers/gpu/drm/tiny/simpledrm.c | 932 +++++++++++++++++++++++++ >>> include/drm/drm_aperture.h | 96 +++ >>> include/drm/drm_fb_helper.h | 56 +- >>> include/drm/drm_format_helper.h | 10 +- >>> 14 files changed, 1466 insertions(+), 60 deletions(-) >>> create mode 100644 drivers/gpu/drm/drm_aperture.c >>> create mode 100644 drivers/gpu/drm/tiny/simpledrm.c >>> create mode 100644 include/drm/drm_aperture.h >>> >>> -- >>> 2.30.1 >>> >> >
