Re: [PATCH v3] tty: hvc: dcc: Detect JTAG connection only on CPU core 0

[sashiko-bot@kernel.org]

> From: Jiannan Du <shatyuka@qq.com>
> 
> On SMP, migration can occur inside hvc_dcc_check() during device_initcall,
> so the CPU writing the probe character and the CPU reading the TXfull
> status may not be the same, which can hang the system.
> 
> Commit 4419da5d5d4b1788568b ("tty: hvc: dcc: Bind driver to CPU core0
> for reads and writes") cached the DCC availability detected on core 0
> during console_initcall. However, this is not sufficient: if core 0
> does not detect DCC as available and another CPU later calls
> hvc_dcc_check(), the check is not actually performed on core 0.
> 
> Since JTAG is not expected to be plugged or unplugged during kernel
> boot, especially between console_initcall and device_initcall, checking
> DCC availability multiple times is unnecessary. Cache the return value
> from hvc_dcc_console_init and reuse it in hvc_dcc_init. This avoids
> complex SMP-related code and ensures the result is always from core 0.
> 
> Signed-off-by: Jiannan Du <shatyuka@qq.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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