On Tue, Mar 30, 2021 at 10:34:12AM +0200, Hans de Goede wrote: > Hi, > > On 3/30/21 9:09 AM, Thomas Zimmermann wrote: > > Hi > > > > Am 29.03.21 um 16:50 schrieb Hans de Goede: > >> 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. > > > > I do as well. And when I boot with simpledrm + native driver it's > > flicker-free from what I can tell. But drm_mode_config_reset() is supposed > > to reset HW and software state. There could be some corner case where we'd > > have to clear the screen. For now, it should be fine. > > Sounds good, thanks.
To clarify: Atomic assumes that the sw state always matches hw state, even at boot-up. Most drivers use drm_mode_config_reset to achieve that, which forces everything to off. But that breaks flicker-free boot. To avoid that i915 (and it's the only driver doing so) has fairly elaborate state-readout code, to make sure we do faithfully preserve the full boot-up display state. This is anything but trivial to implement. For simpledrm it's a bit simple, since state recover boils down to reading out the fb and putting it into the new one, since there's not even provisions (afaiui) for simpledrm to enable/disable the output physically. So i915 is the exception here allowing flicker-free boot, not the rule. -Daniel > > BTW if you have the time I'd appreciate your review of the patchset. > > Sorry, but I'm burried under a whole pile of other work. So although I would > like to help it is better to say no. > > 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-o...@mail.gmail.com/ > >>>>> [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 > >>>>> > >>>> > >>> > >> > >> _______________________________________________ > >> dri-devel mailing list > >> dri-devel@lists.freedesktop.org > >> https://lists.freedesktop.org/mailman/listinfo/dri-devel > >> > > > -- Daniel Vetter Software Engineer, Intel Corporation http://blog.ffwll.ch _______________________________________________ dri-devel mailing list dri-devel@lists.freedesktop.org https://lists.freedesktop.org/mailman/listinfo/dri-devel
