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[2001:1c00:c1e:bf00:1054:9d19:e0f0:8214]) by smtp.gmail.com with ESMTPSA id n25sm9179634edq.55.2021.03.29.07.50.38 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Mon, 29 Mar 2021 07:50:38 -0700 (PDT) Subject: Re: [PATCH v2 00/10] drm: Support simple-framebuffer devices and firmware fbs To: Thomas Zimmermann , daniel@ffwll.ch, airlied@linux.ie, maarten.lankhorst@linux.intel.com, mripard@kernel.org, kraxel@redhat.com, corbet@lwn.net, lgirdwood@gmail.com, broonie@kernel.org, sam@ravnborg.org, robh@kernel.org, emil.l.velikov@gmail.com, geert+renesas@glider.be, bluescreen_avenger@verizon.net Cc: dri-devel@lists.freedesktop.org, linux-doc@vger.kernel.org, virtualization@lists.linux-foundation.org References: <20210318102921.21536-1-tzimmermann@suse.de> From: Hans de Goede Message-ID: Date: Mon, 29 Mar 2021 16:50:38 +0200 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.7.0 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8 Content-Language: en-US Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-doc@vger.kernel.org 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@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 >>> >> >