linux-kernel - Re: [BISECTED] Allwinner A33 tablet does not fully power off

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Message-ID: <c1e8a25e-3fd0-ba28-67a5-6775c6ce2d6d@sholland.org>
Date:   Sat, 5 Nov 2022 14:18:48 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>
Cc:     mripard@...nel.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Merlijn Wajer <merlijn@...zup.org>,
        wens@...e.org
Subject: Re: [BISECTED] Allwinner A33 tablet does not fully power off

On 11/5/22 03:23, Ivaylo Dimitrov wrote:
> Hi Samuel,
> 
> On 5.11.22 г. 4:21 ч., Samuel Holland wrote:
>> Hi Ivo,
>>
>> On 10/29/22 10:23, Ivaylo Dimitrov wrote:
>>> After commit 843107498f91e57d1d4b22cd8787112726fdaeb4 (bus: sunxi-rsb:
>>> Implement suspend/resume/shutdown callbacks) Q8 A33 tablet I have here
>>> cannot be powered-on after power-off, it needs press-and-hold of the
>>> power button for 10 seconds (I guess some HW assisted power down
>>> happens) before it can be powered-on again.
>>>
>>> The following patch makes it behave correctly:
>>>
>>> diff --git a/drivers/bus/sunxi-rsb.c b/drivers/bus/sunxi-rsb.c
>>> index 60b082fe2ed0..30016d62044c 100644
>>> --- a/drivers/bus/sunxi-rsb.c
>>> +++ b/drivers/bus/sunxi-rsb.c
>>> @@ -818,10 +818,7 @@ static int sunxi_rsb_remove(struct platform_device
>>> *pdev)
>>>
>>>   static void sunxi_rsb_shutdown(struct platform_device *pdev)
>>>   {
>>> -       struct sunxi_rsb *rsb = platform_get_drvdata(pdev);
>>> -
>>>          pm_runtime_disable(&pdev->dev);
>>> -       sunxi_rsb_hw_exit(rsb);
>>>   }
>>>
>>>   static const struct dev_pm_ops sunxi_rsb_dev_pm_ops = {
>>>
>>>
>>> I guess the issue comes from the fact that by the time 'power off'
>>> command to the power management IC has to be send, the bus it lives on
>>> is already down, so the device is left in semi-powered down state. Ofc
>>> this is a wild guess, however, preventing the bus being turned off on
>>> shutdown fixes the issue.
>>
>> Your guess is correct. The controller gets shut down in
>>
>>    kernel_power_off()
>>      kernel_shutdown_prepare()
>>        device_shutdown()
>>
>> but the PMIC communication needs to happen later in
>>
>>    kernel_power_off()
>>      machine_power_off()
>>        pm_power_off()
>>
>>> Please LMK if the above is the correct approach so I will send a proper
>>> patch or something else shall be fixed.
>>
>> Yes, this is exactly the right approach. The whole sunxi_rsb_shutdown()
> 
> Don't we need pm_runtime_disable() on shutdown? As IIUC, the controller
> might be suspended and we have to resume it to put it in state to accept
> commands later on(in pm_power_off()).

sunxi_rsb_write() takes care of resuming the controller, so the
controller being suspended prior to pm_power_off() is fine.
pm_runtime_disable() would actually prevent resuming the controller
later in sunxi_rsb_write().

>> function should be removed. When you send a patch, please add a Fixes:
>> tag referencing the commit that you bisected to.

I found a couple of other issues as well, so I'll send out some fixes
with you CC'd.

Regards,
Samuel