Re: Raspberry Pi 3 Model B+ hangs in vc4_hdmi_runtime_resume()

[Maxime Ripard <maxime@cerno.tech>]

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On Tue, Sep 27, 2022 at 03:15:17PM +0200, Maxime Ripard wrote:
> On Tue, Sep 27, 2022 at 02:25:12PM +0200, Maxime Ripard wrote:
> > On Tue, Sep 27, 2022 at 01:42:40PM +0200, Maxime Ripard wrote:
> > > On Tue, Sep 27, 2022 at 01:12:35PM +0200, Stefan Wahren wrote:
> > > > Am 27.09.22 um 11:42 schrieb Maxime Ripard:
> > > > > On Tue, Sep 27, 2022 at 09:25:54AM +0200, Maxime Ripard wrote:
> > > > > > Hi Stefan,
> > > > > > 
> > > > > > On Mon, Sep 26, 2022 at 08:50:12PM +0200, Stefan Wahren wrote:
> > > > > > > Am 26.09.22 um 14:47 schrieb Maxime Ripard:
> > > > > > > > On Mon, Sep 26, 2022 at 02:40:48PM +0200, Marc Kleine-Budde wrote:
> > > > > > > > > On 26.09.2022 14:08:04, Stefan Wahren wrote:
> > > > > > > > > > Hi Marc,
> > > > > > > > > > 
> > > > > > > > > > Am 26.09.22 um 12:21 schrieb Marc Kleine-Budde:
> > > > > > > > > > > On 22.09.2022 17:06:00, Maxime Ripard wrote:
> > > > > > > > > > > > > I'm on a Raspberry Pi 3 Model B+ running current Debian testing ARM64,
> > > > > > > > > > > > > using Debian's v5.19 kernel (Debian's v5.18 was working flawless).
> > > > > > > > > > > > > 
> > > > > > > > > > > > > | [    0.000000] Booting Linux on physical CPU 0x0000000000 [0x410fd034]
> > > > > > > > > > > > > | [    0.000000] Linux version 5.19.0-1-arm64 (debian-kernel@lists.debian.org) (gcc-11 (Debian 11.3.0-5) 11.3.0, GNU ld (GNU Binutils for Debian) 2.38.90.20220713) #1 SMP Debian 5.19.6-1 (2022-0
> > > > > > > > > > > > > 9-01)
> > > > > > > > > > > > > | [    0.000000] Machine model: Raspberry Pi 3 Model B+
> > > > > > > > > > > > > | [    3.747500] raspberrypi-firmware soc:firmware: Attached to firmware from 2022-03-24T13:21:11
> > > > > > > > > > > > > 
> > > > > > > > > > > > > As soon a the vc4 module is loaded the following warnings hits 4
> > > > > > > > > > > > > times, then the machine stops.
> > > > > > > > > > > [...]
> > > > > > > > > > > 
> > > > > > > > > > > > The warning itself is fixed, both upstream and in stable (5.19.7).
> > > > > > > > > > > Ok. Debian is using 5.19.6
> > > > > > > > > > > 
> > > > > > > > > > > > It shouldn't have any relation to the hang though. Can you share your
> > > > > > > > > > > > setup?
> > > > > > > > > > > - config.txt:
> > > > > > > > > > > 
> > > > > > > > > > > -------->8-------->8-------->8-------->8--------
> > > > > > > > > > > gpu_mem=16
> > > > > > > > > > > disable_splash=1
> > > > > > > > > > > 
> > > > > > > > > > > arm_64bit=1
> > > > > > > > > > > enable_uart=1
> > > > > > > > > > > uart_2ndstage=1
> > > > > > > > > > > 
> > > > > > > > > > > os_prefix=/u-boot/
> > > > > > > > > > > 
> > > > > > > > > > > [pi3]
> > > > > > > > > > > force_turbo=1
> > > > > > > > > > > -------->8-------->8-------->8-------->8--------
> > > > > > > > > > > 
> > > > > > > > > > > - Raspberry Pi 3 Model B+
> > > > > > > > > > > - no HDMI connected
> > > > > > > > > > Does it mean, the issue only occurs without HDMI connected?
> > > > > > > > > > If you didn't test with HDMI yet, could you please do?
> > > > > > > > > The error occurs with HDMI not connected, as vc4 is the gfx driver I
> > > > > > > > > thought this might be of interest. :)
> > > > > > > > > 
> > > > > > > > > I don't have a HDMI monitor here, but I'll come back to you as soon as I
> > > > > > > > > get access to one (might take some time).
> > > > > > > > It's not the first time an issue like this one would occur. I'm trying
> > > > > > > > to make my Pi3 boot again, and will try to bisect the issue.
> > > > > > > yes the issue is only triggered without HDMI connected. I was able to
> > > > > > > reproduce with an older vc4 firmware from 2020 (don't want to upgrade yet).
> > > > > > > Kernel was also an arm64 build with defconfig.
> > > > > > > 
> > > > > > > Here some rough starting point for bisection:
> > > > > > > 
> > > > > > > 5.18.0 good
> > > > > > > 5.19.0 bad
> > > > > > > 5.19.6 bad
> > > > > > Sorry it took a bit of time, it looks like I found another bug while
> > > > > > trying to test this yesterday.
> > > > > > 
> > > > > > Your datapoints are interesting though. I have a custom configuration
> > > > > > and it does boot 5.19 without an HDMI connected.
> > > > > > 
> > > > > > So I guess it leaves us with either the firmware version being different
> > > > > > (I'm using a newer version, from March 2022), or the configuration. I'll
> > > > > > test with defconfig.
> > > > > So it turns out compiling vc4 as a module is the culprit.
> > > > 
> > > > Do you mean regardless of the kernel version in your case?
> > > 
> > > No, I mean that, with vc4 as a module, 5.18 works but 5.19 doesn't, like
> > > Marc said. But if vc4 is built in, both work.
> > > 
> > > > In my test cases i build vc4 always as module.
> > > > 
> > > > > It's not clear to me why at this point, but the first register write in
> > > > > vc4_hdmi_reset stalls.
> > > >
> > > > Sounds like timing issue or a missing dependency (clock or power domain)
> > > 
> > > It felt like a clock or power domain issue to me indeed, but adding
> > > clk_ignore_unused and pd_ignore_unused isn't enough, so it's probably
> > > something a bit more complicated than just the clock / PD being
> > > disabled.
> > 
> > I found the offending patch:
> > https://lore.kernel.org/dri-devel/20220225143534.405820-13-maxime@cerno.tech/
> > 
> > That code was removed because it was made irrelevant by that earlier patch:
> > https://lore.kernel.org/dri-devel/20220225143534.405820-10-maxime@cerno.tech/
> > 
> > But it turns out that while it works when the driver is built-in, it
> > doesn't when it's a module. If we add a clk_hw_get_rate() call right
> > after that call to raspberrypi_fw_set_rate(), the rate returned is 0.
> > 
> > I'm not entirely sure why, but I wonder if it's related to:
> > https://github.com/raspberrypi/linux/issues/4962#issuecomment-1228593439
> 
> Turns out it's not, since the Pi3 is using the clk-bcm2835 driver.
> 
> However, even reverting that patch fails. clk_set_min_rate fails because
> the rate is protected, but it doesn't look like it is anywhere for that
> clock, so I'm a bit confused.
> 
> Even if we do remove the clock protection check in
> clk_core_set_rate_nolock(), clk_calc_new_rates() will then fail because
> the bcm2835 driver will round the clock rate below the minimum, which is
> rejected.
> 
> I'm not entirely sure what to do at this point. I guess the proper fix
> would be to:
>   - Figure out why it's considered protected when it's not (or shouldn't be)
>   - Make the driver compute an acceptable rate for that clock

This was due to 5.19.7 missing 88110a9f6209

>   - Reintroduce the clk_set_min_rate call to HDMI's runtime_resume, or
>     some other equivalent code

I just sent a series addressing this here:
https://lore.kernel.org/r/20220929-rpi-pi3-unplugged-fixes-v1-0-cd22e962296c@cerno.tech

Thanks for the report and the help :)
Maxime

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