Re: [PATCH 0/2] clk: fix the need of booking clk_ignore_unused=true on embedded devs

[Mauro Carvalho Chehab <mchehab+huawei@kernel.org>]

Stephen/Michael,

Gentile ping.

Regards,
Mauro

Em Thu,  7 Oct 2021 14:06:53 +0200
Mauro Carvalho Chehab <mchehab+huawei@kernel.org> escreveu:

> Currently, the only way to boot a Kernel with drivers built as modules on embedded 
> devices like HiKey 970 is to pass clk_ignore_unused=true as a modprobe parameter.
> 
> There are two separate issues:
> 
> 1. the clk's core calls clk_disable_unused() too early. By the time this
>    function is called, only the builtin drivers were already probed/initialized.
>    Drivers built as modules will only be probed afterwards.
> 
>    This cause a race condition and boot instability, as the clk core will try
>    to disable clocks while the drivers built as modules are still being
>    probed and initialized.
> 
>    I suspect that the same problem used to happen at the regulator's core,
>    as there's a code that waits for 30 seconds before disabling unused
>    regulators;
> 
> 2. there are some gate clocks defined at HiKey 970 that should always be on,
>    as otherwise the system will hang, or the filesystem I/O will stop.
> 
> Ps.: 
>   I submitted already 3 or 4 versions of patches for HiKey 970 clock, but
>   they're all unreliable, due to the race conditions at the clk core due to (1).
>    
> Patch 1 solves the issue with the clk core.
> Patch 2 solves the HiKey 970 specific issues.
> 
> Mauro Carvalho Chehab (2):
>   clk: wait for extra time before disabling unused clocks
>   clk: clk-hi3670: mark some clocks as CLK_IS_CRITICAL
> 
>  drivers/clk/clk.c                  | 51 +++++++++++++++++++-----------
>  drivers/clk/hisilicon/clk-hi3670.c | 24 +++++++-------
>  2 files changed, 44 insertions(+), 31 deletions(-)
>