On 9/2/24 18:58, Daniel Vetter wrote: > On Thu, Feb 08, 2024 at 09:16:50AM +0800, Daniel van Vugt wrote: >> On 8/2/24 04:21, Mario Limonciello wrote: >>> On 2/7/2024 03:51, Daniel Vetter wrote: >>>> On Wed, Feb 07, 2024 at 10:03:10AM +0800, Daniel van Vugt wrote: >>>>> On 6/2/24 23:41, Mario Limonciello wrote: >>>>>> On 2/6/2024 08:21, Daniel Vetter wrote: >>>>>>> On Tue, Feb 06, 2024 at 06:10:51PM +0800, Daniel van Vugt wrote: >>>>>>>> Until now, deferred console takeover only meant defer until there is >>>>>>>> output. But that risks stepping on the toes of userspace splash screens, >>>>>>>> as console messages may appear before the splash screen. So check the >>>>>>>> command line for the expectation of userspace splash and if present then >>>>>>>> extend the deferral until after the first switch. >>>>>>>> >>>>>>>> V2: Added Kconfig option instead of hard coding "splash". >>>>>>>> >>>>>>>> Closes: https://bugs.launchpad.net/bugs/1970069 >>>>>>>> Cc: Mario Limonciello <mario.limonciello@xxxxxxx> >>>>>>>> Signed-off-by: Daniel van Vugt <daniel.van.vugt@xxxxxxxxxxxxx> >>>>>>>> --- >>>>>>>> drivers/video/console/Kconfig | 13 +++++++++++ >>>>>>>> drivers/video/fbdev/core/fbcon.c | 38 ++++++++++++++++++++++++++++++-- >>>>>>>> 2 files changed, 49 insertions(+), 2 deletions(-) >>>>>>>> >>>>>>>> diff --git a/drivers/video/console/Kconfig b/drivers/video/console/Kconfig >>>>>>>> index bc31db6ef7..a6e371bfb4 100644 >>>>>>>> --- a/drivers/video/console/Kconfig >>>>>>>> +++ b/drivers/video/console/Kconfig >>>>>>>> @@ -138,6 +138,19 @@ config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>>>> by the firmware in place, rather then replacing the contents with a >>>>>>>> black screen as soon as fbcon loads. >>>>>>>> +config FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>>>> + string "Framebuffer Console Deferred Takeover Condition" >>>>>>>> + depends on FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>>>> + default "splash" >>>>>>>> + help >>>>>>>> + If enabled this defers further the framebuffer console taking over >>>>>>>> + until the first console switch has occurred. And even then only if >>>>>>>> + text has been output, and only if the specified parameter is found >>>>>>>> + on the command line. This ensures fbcon does not interrupt userspace >>>>>>>> + splash screens such as Plymouth which may be yet to start rendering >>>>>>>> + at the time of the first console output. "splash" is the simplest >>>>>>>> + distro-agnostic condition for this that Plymouth checks for. >>>>>>> >>>>>>> Hm this seems a bit strange since a lot of complexity that no one needs, >>>>>>> also my impression is that it's rather distro specific how you want this >>>>>>> to work. So why not just a Kconfig option that lets you choose how much >>>>>>> you want to delay fbcon setup, with the following options: >>>>>>> >>>>>>> - no delay at all >>>>>>> - dely until first output from the console (which then works for distros >>>>>>> which set a log-level to suppress unwanted stuff) >>>>>>> - delay until first vt-switch. In that case I don't think we also need to >>>>>>> delay for first output, since vt switch usually means you'll get first >>>>>>> output right away (if it's a vt terminal) or you switch to a different >>>>>>> graphical console (which will keep fbcon fully suppressed on the drm >>>>>>> side). >>>>>>> >>>>> >>>>> I had similar thoughts, and had prototyped some of this already. But in the end >>>>> it felt like extra complexity there was no demand for. >>>> >>>> For me this one is a bit too complex, since if you enable the vt switch >>>> delay you also get the output delay on top. That seems one too much and I >>>> can't come up with a use-case where you actually want that. So just a >>>> choice of one or the other or none feels cleaner. >> >> Remember the output "delay" goes to zero if any putc has occurred prior to >> registration (see dummycon.c). >> >> My current reason for using both is that in theory it prevents fbcon from >> taking over *earlier* than it did before, in case there was never any output. >> But I don't think there is "never any output" by the time you've tried to >> manually VT switch so maybe that's unnecessary. > > Yeah, but I'm not sure that's like a choice anyone needs, just these > three: > > - no delay > - wait until first output, and set debuglevel appropriately (what fedora > and other distros do) > - wait until first vt switch (what ubuntu wants) Come to think of it, an enum or Kconfig "choice" isn't necessary if I change the default for CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION to blank/disabled. Then the default behaviour is unchanged and you've still got the choice of all three modes: - No delay: fbcon=nodefer - Wait until first output: Already happens when CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION is absent from the command line. - Wait until first VT switch: Would only happen if compiled with CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION and its value is present on the command line. P.S. I suspect Fedora and other distros are not immune to the problem, just make it less likely by starting Plymouth super early on simpledrm. Certainly I am finding some models of laptop emit kernel messages that would still pass under a reduced loglevel. > > I don't ever expect fedora to just enable this, because they have > something that works. Plus many distros are moving away from CONFIG_VT and > all the in-kernel consoles anyway, so they want this even less. > > So if just the delay to first vt-switch is enough for you, I think it's > best we just implement that. The entire vt switch/ownership rules with drm > and fbdev and all that is already really complex and in many cases it's > impossible to tell what's accidental cargo-culted behaviour and what is > actually required. That's why I'd prefer we exactly implement what you > need in this area, nothing more, nothing less. > > And from the testing you discuss below it sounds like you don't need both > delays? > > Cheers, Sima > >>>>> If you would like to specify the preferred Kconfig design then I can implement >>>>> it. Though I don't think there is an enumeration type. It could also be a >>>>> runtime enumeration (deferred_takeover) controlled by fbcon=something. >>>> >>>> There's a choice in Kconfig, see e.g. kernel/Kconfig.hz for an example. >> >> Thanks! >> >>>> >>>>>> IIUC there is an "automatic" VT switch that happens with Ubuntu GRUB + Ubuntu >>>>>> kernels. >>>>>> >>>>>> Why? >>>>>> >>>>>> Couldn't this also be suppressed by just not doing that? >>>>> >>>>> I have not seen any automatic VT switches in debugging but now that you mention >>>>> it I was probably only debugging on drm-misc-next and not an Ubuntu kernel. >>>> >>>> Hm but I don't see how the output delay would paper over a race (if there >>>> is one) reliable for this case? If you do vt switch for boot splash or >>>> login screen and don't yet have drm opened for display or something like >>>> that, then fbcon can sneak in anyway ... >> >> There is no VT switch according to my logs, so there is no race with the >> patchset. The only race that occurs is without this patchset, which is what's >> being fixed here. >> >>> >>> Ubuntu has had in (at least some) kernels: >>> >>> https://git.launchpad.net/~ubuntu-kernel/ubuntu/+source/linux/+git/unstable/commit/?id=320cfac8ef31 >>> >>> I'm unsure if it's still there today, but maybe it would be best if the author >>> (Andy) could enlighten us? Any idea why that didn't go upstream? >>> >>> I had thought that tied with a automatic VT switch that was trying to hide >>> fbcon as well. >> >> I checked the current Ubuntu 24.04 kernel yesterday and there is no VT switch >> (anymore). The vc_num stays at zero until you do a manual VT switch. This seems >> to be true for both drm-misc-next and Ubuntu kernels. >> >> There is still vt.handoff=7 on the command line for Ubuntu, but I'm not sure it >> has a function anymore. Maybe it was primarily for legacy BIOS? Andy can confirm. >> >>> >>>> >>>> Cheers, Sima >>>>> >>>>> - Daniel >>>>> >>>>>> >>>>>>> I think you could even reuse the existing >>>>>>> CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER for this, and then just >>>>>>> compile-time select which kind of notifier to register (well plus the >>>>>>> check for "splash" on the cmdline for the vt switch one I guess). >>>>>>> >>>>>>> Thoughts? >>>>>>> >>>>>>> Cheers, Sima >>>>>>> >>>>>>> >>>>>>>> + >>>>>>>> config STI_CONSOLE >>>>>>>> bool "STI text console" >>>>>>>> depends on PARISC && HAS_IOMEM >>>>>>>> diff --git a/drivers/video/fbdev/core/fbcon.c >>>>>>>> b/drivers/video/fbdev/core/fbcon.c >>>>>>>> index 63af6ab034..98155d2256 100644 >>>>>>>> --- a/drivers/video/fbdev/core/fbcon.c >>>>>>>> +++ b/drivers/video/fbdev/core/fbcon.c >>>>>>>> @@ -76,6 +76,7 @@ >>>>>>>> #include <linux/crc32.h> /* For counting font checksums */ >>>>>>>> #include <linux/uaccess.h> >>>>>>>> #include <asm/irq.h> >>>>>>>> +#include <asm/cmdline.h> >>>>>>>> #include "fbcon.h" >>>>>>>> #include "fb_internal.h" >>>>>>>> @@ -3358,6 +3359,26 @@ static int fbcon_output_notifier(struct >>>>>>>> notifier_block *nb, >>>>>>>> return NOTIFY_OK; >>>>>>>> } >>>>>>>> + >>>>>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>>>> +static int initial_console; >>>>>>>> +static struct notifier_block fbcon_switch_nb; >>>>>>>> + >>>>>>>> +static int fbcon_switch_notifier(struct notifier_block *nb, >>>>>>>> + unsigned long action, void *data) >>>>>>>> +{ >>>>>>>> + struct vc_data *vc = data; >>>>>>>> + >>>>>>>> + WARN_CONSOLE_UNLOCKED(); >>>>>>>> + >>>>>>>> + if (vc->vc_num != initial_console) { >>>>>>>> + dummycon_unregister_switch_notifier(&fbcon_switch_nb); >>>>>>>> + dummycon_register_output_notifier(&fbcon_output_nb); >>>>>>>> + } >>>>>>>> + >>>>>>>> + return NOTIFY_OK; >>>>>>>> +} >>>>>>>> +#endif >>>>>>>> #endif >>>>>>>> static void fbcon_start(void) >>>>>>>> @@ -3370,7 +3391,16 @@ static void fbcon_start(void) >>>>>>>> if (deferred_takeover) { >>>>>>>> fbcon_output_nb.notifier_call = fbcon_output_notifier; >>>>>>>> - dummycon_register_output_notifier(&fbcon_output_nb); >>>>>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>>>> + if (cmdline_find_option_bool(boot_command_line, >>>>>>>> + CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION)) { >>>>>>>> + initial_console = fg_console; >>>>>>>> + fbcon_switch_nb.notifier_call = fbcon_switch_notifier; >>>>>>>> + dummycon_register_switch_notifier(&fbcon_switch_nb); >>>>>>>> + } else >>>>>>>> +#endif >>>>>>>> + dummycon_register_output_notifier(&fbcon_output_nb); >>>>>>>> + >>>>>>>> return; >>>>>>>> } >>>>>>>> #endif >>>>>>>> @@ -3417,8 +3447,12 @@ void __exit fb_console_exit(void) >>>>>>>> { >>>>>>>> #ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER >>>>>>>> console_lock(); >>>>>>>> - if (deferred_takeover) >>>>>>>> + if (deferred_takeover) { >>>>>>>> dummycon_unregister_output_notifier(&fbcon_output_nb); >>>>>>>> +#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER_CONDITION >>>>>>>> + dummycon_unregister_switch_notifier(&fbcon_switch_nb); >>>>>>>> +#endif >>>>>>>> + } >>>>>>>> console_unlock(); >>>>>>>> cancel_work_sync(&fbcon_deferred_takeover_work); >>>>>>>> -- >>>>>>>> 2.43.0 >>>>>>>> >>>>>>> >>>>>> >>>> >>> >
