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UPSTREAM: serial: 8250_mtk: Simplify clock sequencing and runtime PM

Vitor Sato Eschholz requested to merge vsatoes/uart-s3 into mtk-android12-5.10

When testing deep suspend/resume we could observe some issues when getting back the secondary CPUS online:

[   51.848362] PM: suspend entry (deep)                                            
[   51.977044] Filesystems sync: 0.128 seconds                                           
[   53.995078] Freezing user space processes ... (elapsed 0.005 seconds) done.     
[   54.001618] OOM killer disabled.                                                
[   54.002032] Freezing remaining freezable tasks ... (elapsed 0.002 seconds) done.
[   54.005610] printk: Suspending console(s) (use no_console_suspend to debug)     
)3dڷitializing                                                                     
I/TC: Secondary CPU 1 switching to normal world boot                               
I/TC: Secondary CPU 2 initializing                                                 
I/TC: Secondary CPU 2 switching to normal world boot                               
I/TC: Secondary CPU 3 initializing                                                 
I/TC: Secondary CPU 3 switching to normal world boot                               
[   54.009019] Bluetooth: hci0: status (0) return ownership to device              
[   54.182590] Disabling non-boot CPUs ...                                         
[   54.184062] psci: CPU1 killed (polled 4 ms)                                     
[   54.188114] psci: CPU2 killed (polled 4 ms)                                     
[   54.192112] psci: CPU3 killed (polled 4 ms)                                     
[   54.194418] PM: pm_system_irq_wakeup: 46 triggered volume_up                    
[   54.194524] Enabling non-boot CPUs ...                                          
[   59.370478] CPU1: failed to come online                                         
[   59.370487] CPU1: failed in unknown state : 0x0                                 
[   59.371150] Error taking CPU1 up: -5                                            
[   64.490566] CPU2: failed to come online                                         
[   64.490574] CPU2: failed in unknown state : 0x0                                 
[   64.491254] Error taking CPU2 up: -5                                            
[   69.610662] CPU3: failed to come online                                         
[   69.610669] CPU3: failed in unknown state : 0x0                                 
[   69.611291] Error taking CPU3 up: -5

By disabling the uart, or letting console enabled during suspend, issue was not observed.

Fix it by applying upstream patch.

The 8250_mtk driver's runtime PM support has some issues:

  • The bus clock is enabled (through runtime PM callback) later than a register write
  • runtime PM resume callback directly called in probe, but no pm_runtime_set_active() call is present
  • UART PM function calls the callbacks directly, and calls runtime PM API
  • runtime PM callbacks try to do reference counting, adding yet another count between runtime PM and clocks

This fragile setup worked in a way, but broke recently with runtime PM support added to the serial core. The system would hang when the UART console was probed and brought up.

Tony provided some potential fixes [1][2], though they were still a bit complicated. The 8250_dw driver, which the 8250_mtk driver might have been based on, has a similar structure but simpler runtime PM usage.

Simplify clock sequencing and runtime PM support in the 8250_mtk driver. Specifically, the clock is acquired enabled and assumed to be active, unless toggled through runtime PM suspend/resume. Reference counting is removed and left to the runtime PM core. The serial pm function now only calls the runtime PM API.

[1] https://lore.kernel.org/linux-serial/20230602092701.GP14287@atomide.com/ [2] https://lore.kernel.org/linux-serial/20230605061511.GW14287@atomide.com/

Fixes: 84a9582f ("serial: core: Start managing serial controllers to enable runtime PM") Suggested-by: Tony Lindgren tony@atomide.com Signed-off-by: Chen-Yu Tsai wenst@chromium.org Reviewed-by: AngeloGioacchino Del Regno angelogioacchino.delregno@collabora.com Reviewed-by: Tony Lindgren tony@atomide.com Message-ID: 20230606091747.2031168-1-wenst@chromium.org Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org (cherry picked from commit b6c7ff26) Signed-off-by: Vitor Sato Eschholz vsatoes@baylibre.com

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