[PATCH] serial: imx: Add missing .thaw_noirq hook

[Martin Kaiser]

Thus wrote Shawn Guo (shawn.guo at linaro.org):

> The following warning is seen with non-console UART instance when
> system hibernates.

> [   37.371969] ------------[ cut here ]------------
> [   37.376599] uart3_root_clk already disabled
> [   37.380810] WARNING: CPU: 0 PID: 296 at drivers/clk/clk.c:952 clk_core_disable+0xa4/0xb0
> ...
> [   37.506986] Call trace:
> [   37.509432]  clk_core_disable+0xa4/0xb0
> [   37.513270]  clk_disable+0x34/0x50
> [   37.516672]  imx_uart_thaw+0x38/0x5c
> [   37.520250]  platform_pm_thaw+0x30/0x6c
> [   37.524089]  dpm_run_callback.constprop.0+0x3c/0xd4
> [   37.528972]  device_resume+0x7c/0x160
> [   37.532633]  dpm_resume+0xe8/0x230
> [   37.536036]  hibernation_snapshot+0x288/0x430
> [   37.540397]  hibernate+0x10c/0x2e0
> [   37.543798]  state_store+0xc4/0xd0
> [   37.547203]  kobj_attr_store+0x1c/0x30
> [   37.550953]  sysfs_kf_write+0x48/0x60
> [   37.554619]  kernfs_fop_write_iter+0x118/0x1ac
> [   37.559063]  new_sync_write+0xe8/0x184
> [   37.562812]  vfs_write+0x230/0x290
> [   37.566214]  ksys_write+0x68/0xf4
> [   37.569529]  __arm64_sys_write+0x20/0x2c
> [   37.573452]  invoke_syscall.constprop.0+0x50/0xf0
> [   37.578156]  do_el0_svc+0x11c/0x150
> [   37.581648]  el0_svc+0x30/0x140
> [   37.584792]  el0t_64_sync_handler+0xe8/0xf0
> [   37.588976]  el0t_64_sync+0x1a0/0x1a4
> [   37.592639] ---[ end trace 56e22eec54676d75 ]---

> On hibernating, pm core calls into related hooks in sequence like:

>     .freeze
>     .freeze_noirq
>     .thaw_noirq
>     .thaw

> With .thaw_noirq hook being absent, the clock will be disabled in a
> unbalanced call which results the warning above.

>     imx_uart_freeze()
>         clk_prepare_enable()
>     imx_uart_suspend_noirq()
>         clk_disable()
>     imx_uart_thaw
>         clk_disable_unprepare()

> Adding the missing .thaw_noirq hook as imx_uart_resume_noirq() will have
> the call sequence corrected as below and thus fix the warning.

>     imx_uart_freeze()
>         clk_prepare_enable()
>     imx_uart_suspend_noirq()
>         clk_disable()
>     imx_uart_resume_noirq()
>         clk_enable()
>     imx_uart_thaw
>         clk_disable_unprepare()

> Signed-off-by: Shawn Guo <shawn.guo at linaro.org>
> ---
>  drivers/tty/serial/imx.c | 1 +
>  1 file changed, 1 insertion(+)

> diff --git a/drivers/tty/serial/imx.c b/drivers/tty/serial/imx.c
> index 590a25369531..e5163c2c4169 100644
> --- a/drivers/tty/serial/imx.c
> +++ b/drivers/tty/serial/imx.c
> @@ -2603,6 +2603,7 @@ static const struct dev_pm_ops imx_uart_pm_ops = {
>  	.suspend_noirq = imx_uart_suspend_noirq,
>  	.resume_noirq = imx_uart_resume_noirq,
>  	.freeze_noirq = imx_uart_suspend_noirq,
> +	.thaw_noirq = imx_uart_resume_noirq,
>  	.restore_noirq = imx_uart_resume_noirq,
>  	.suspend = imx_uart_suspend,
>  	.resume = imx_uart_resume,
> -- 
> 2.25.1

Reviewed-by: Martin Kaiser <martin at kaiser.cx>

Thanks,

   Martin