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

[Shawn Guo]

On Wed, Oct 12, 2022 at 06:20:35PM +0200, Greg Kroah-Hartman wrote:
> On Wed, Oct 12, 2022 at 08:13:53PM +0800, Shawn Guo wrote:
> > 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>
> 
> What commit id does this fix, and does it need to go to older/stable
> kernels?

The .thaw_noirq was missing from commit 94be6d74d040 ("serial: imx: add
hibernation support"), but it did not cause the warning until commit
09df0b3464e5 ("serial: imx: fix endless loop during suspend") changes
clock calls.  So I should have added:

Fixes: 09df0b3464e5 ("serial: imx: fix endless loop during suspend")

Shawn