[PATCH v2 00/10] drm: Support simple-framebuffer devices and firmware fbs
Daniel Vetter
daniel at ffwll.ch
Thu Apr 8 10:14:06 UTC 2021
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 at 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 at 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@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
> >>>>>
> >>>>
> >>>
> >>
> >> _______________________________________________
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> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >>
> >
>
--
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch
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