linux-kernel - Re: [PATCH v2 00/41] drm: Analog TV Improvements

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Date:   Sat, 24 Sep 2022 17:33:05 +0200
From:   Noralf Trønnes <noralf@...nnes.org>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Stefan Wahren <stefan.wahren@...e.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        Lyude Paul <lyude@...hat.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Rodrigo Vivi <rodrigo.vivi@...el.com>,
        Tvrtko Ursulin <tvrtko.ursulin@...ux.intel.com>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Samuel Holland <samuel@...lland.org>,
        Karol Herbst <kherbst@...hat.com>,
        Emma Anholt <emma@...olt.net>, Daniel Vetter <daniel@...ll.ch>,
        Joonas Lahtinen <joonas.lahtinen@...ux.intel.com>,
        Dom Cobley <dom@...pberrypi.com>,
        Hans de Goede <hdegoede@...hat.com>,
        linux-arm-kernel@...ts.infradead.org,
        Phil Elwell <phil@...pberrypi.com>,
        intel-gfx@...ts.freedesktop.org,
        Dave Stevenson <dave.stevenson@...pberrypi.com>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        nouveau@...ts.freedesktop.org, linux-sunxi@...ts.linux.dev,
        Mateusz Kwiatkowski <kfyatek+publicgit@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Noralf Trønnes <noralf@...nnes.org>
Subject: Re: [PATCH v2 00/41] drm: Analog TV Improvements



Den 21.09.2022 16.03, skrev Maxime Ripard:
> On Wed, Sep 07, 2022 at 06:44:53PM +0200, Noralf Trønnes wrote:
>>
>>
>> Den 07.09.2022 12.36, skrev Stefan Wahren:
>>> Hi Maxime,
>>>
>>> Am 05.09.22 um 16:57 schrieb Maxime Ripard:
>>>> On Fri, Sep 02, 2022 at 01:28:16PM +0200, Noralf Trønnes wrote:
>>>>>
>>>>> Den 01.09.2022 21.35, skrev Noralf Trønnes:
>>>>>>
>>>>>> I have finally found a workaround for my kernel hangs.
>>>>>>
>>>>>> Dom had a look at my kernel and found that the VideoCore was fine, and
>>>>>> he said this:
>>>>>>
>>>>>>> That suggests cause of lockup was on arm side rather than VC side.
>>>>>>>
>>>>>>> But it's hard to diagnose further. Once you've had a peripheral not
>>>>>>> respond, the AXI bus locks up and no further operations are possible.
>>>>>>> Usual causes of this are required clocks being stopped or domains
>>>>>>> disabled and then trying to access the hardware.
>>>>>>>
>>>>>> So when I got this on my 64-bit build:
>>>>>>
>>>>>> [  166.702171] SError Interrupt on CPU1, code 0x00000000bf000002 --
>>>>>> SError
>>>>>> [  166.702187] CPU: 1 PID: 8 Comm: kworker/u8:0 Tainted: G        W
>>>>>>      5.19.0-rc6-00096-gba7973977976-dirty #1
>>>>>> [  166.702200] Hardware name: Raspberry Pi 4 Model B Rev 1.1 (DT)
>>>>>> [  166.702206] Workqueue: events_freezable_power_
>>>>>> thermal_zone_device_check
>>>>>> [  166.702231] pstate: 200000c5 (nzCv daIF -PAN -UAO -TCO -DIT -SSBS
>>>>>> BTYPE=--)
>>>>>> [  166.702242] pc : regmap_mmio_read32le+0x10/0x28
>>>>>> [  166.702261] lr : regmap_mmio_read+0x44/0x70
>>>>>> ...
>>>>>> [  166.702606]  bcm2711_get_temp+0x58/0xb0 [bcm2711_thermal]
>>>>>>
>>>>>> I wondered if that reg read was stalled due to a clock being stopped.
>>>>>>
>>>>>> Lo and behold, disabling runtime pm and keeping the vec clock running
>>>>>> all the time fixed it[1].
>>>>>>
>>>>>> I don't know what the problem is, but at least I can now test this
>>>>>> patchset.
>>>>>>
>>>>>> [1] https://gist.github.com/notro/23b984e7fa05cfbda2db50a421cac065
>>>>>>
>>>>> It turns out I didn't have to disable runtime pm:
>>>>> https://gist.github.com/notro/0adcfcb12460b54e54458afe11dc8ea2
>>>> If the bcm2711_thermal IP needs that clock to be enabled, it should grab
>>>> a reference itself, but it looks like even the device tree binding
>>>> doesn't ask for one.
>>> The missing clock in the device tree binding is expected, because
>>> despite of the code there is not much information about the BCM2711
>>> clock tree. But i'm skeptical that the AVS IP actually needs the VEC
>>> clock, i think it's more likely that the VEC clock parent is changed and
>>> that cause this issue. I could take care of the bcm2711 binding & driver
>>> if i know which clock is really necessary.
>>
>> Seems you're right, keeping the parent always enabled is enough:
>>
>> 	clk_prepare_enable(clk_get_parent(vec->clock)); // pllc_per
>>
>> I tried enabling just the grandparent clock as well, but that didn't help.
> 
> Yeah, adding tracing to the clock framework shows that it indeed
> disables PLLC_PER. So there's probably some other device that depends on
> it but doesn't take a reference to it.
> 
> I had a look, but it's not really obvious what that might be.
> 
> This patch makes sure that the PLL*_PER are never disabled, could you
> test it? It seems to work for me.
> 
> 
> diff --git a/drivers/clk/bcm/clk-bcm2835.c b/drivers/clk/bcm/clk-bcm2835.c
> index 48a1eb9f2d55..3839261ee419 100644
> --- a/drivers/clk/bcm/clk-bcm2835.c
> +++ b/drivers/clk/bcm/clk-bcm2835.c
> @@ -1675,7 +1675,7 @@ static const struct bcm2835_clk_desc clk_desc_array[] = {
>  		.load_mask = CM_PLLA_LOADPER,
>  		.hold_mask = CM_PLLA_HOLDPER,
>  		.fixed_divider = 1,
> -		.flags = CLK_SET_RATE_PARENT),
> +		.flags = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT),
>  	[BCM2835_PLLA_DSI0]	= REGISTER_PLL_DIV(
>  		SOC_ALL,
>  		.name = "plla_dsi0",
> @@ -1784,7 +1784,7 @@ static const struct bcm2835_clk_desc clk_desc_array[] = {
>  		.load_mask = CM_PLLC_LOADPER,
>  		.hold_mask = CM_PLLC_HOLDPER,
>  		.fixed_divider = 1,
> -		.flags = CLK_SET_RATE_PARENT),
> +		.flags = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT),
> 

Yes, this worked, but it's enough to mark pllc_per as critical.

Noralf.

>  	/*
>  	 * PLLD is the display PLL, used to drive DSI display panels.
> @@ -1891,7 +1891,7 @@ static const struct bcm2835_clk_desc clk_desc_array[] = {
>  		.load_mask = CM_PLLH_LOADAUX,
>  		.hold_mask = 0,
>  		.fixed_divider = 1,
> -		.flags = CLK_SET_RATE_PARENT),
> +		.flags = CLK_IS_CRITICAL | CLK_SET_RATE_PARENT),
>  	[BCM2835_PLLH_PIX]	= REGISTER_PLL_DIV(
>  		SOC_BCM2835,
>  		.name = "pllh_pix",
> 
> 
> Maxime