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

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Message-ID: <214ed3e0-5959-8fa7-8d66-196e33112cb0@sholland.org>
Date:   Fri, 4 Nov 2022 21:21:23 -0500
From:   Samuel Holland <samuel@...lland.org>
To:     Ivaylo Dimitrov <ivo.g.dimitrov.75@...il.com>, wens@...e.org
Cc:     mripard@...nel.org, linux-sunxi@...ts.linux.dev,
        linux-kernel@...r.kernel.org, Merlijn Wajer <merlijn@...zup.org>
Subject: Re: [BISECTED] Allwinner A33 tablet does not fully power off

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

Regards,
Samuel