[RFC PATCH 06/10] uthread: add cooperative multi-tasking interface

[Yao Zi]

On Fri, Feb 14, 2025 at 03:00:21PM +0100, Jerome Forissier wrote:
> Add an new internal API called uthread (Kconfig symbol: UTHREAD) which
> provides cooperative multi-tasking. The goal is to be able to improve
> the performance of some parts of U-Boot by overlapping lengthy
> operations. Each uthread has its own stack allocated on the heap. The
> default stack size is defined by the UTHREAD_STACK_SIZE symbol and is
> used when uthread_create() is passed zero for the stack_sz argument.
> 
> The implementation is based on context-switching via initjmp()/setjmp()/
> longjmp() and is inspired from barebox threads [1].
> 
> [1] https://github.com/barebox/barebox/blob/master/common/bthread.c
> 
> Signed-off-by: Jerome Forissier <jerome.forissier at linaro.org>
> ---
>  include/uthread.h |  31 ++++++++++++++
>  lib/Kconfig       |  19 ++++++++
>  lib/Makefile      |   2 +
>  lib/uthread.c     | 107 ++++++++++++++++++++++++++++++++++++++++++++++
>  4 files changed, 159 insertions(+)
>  create mode 100644 include/uthread.h
>  create mode 100644 lib/uthread.c
> 
> diff --git a/lib/Kconfig b/lib/Kconfig
> index 1a683dea670..c3416bbd0be 100644
> --- a/lib/Kconfig
> +++ b/lib/Kconfig
> @@ -1255,6 +1255,25 @@ config PHANDLE_CHECK_SEQ
>  	  enable this config option to distinguish them using
>  	  phandles in fdtdec_get_alias_seq() function.
>  
> +config UTHREAD
> +	bool "Enable thread support"
> +	depends on HAVE_INITJMP
> +	help
> +	  Implement a simple form of cooperative multi-tasking based on
> +	  context-switching via initjmp(), setjmp() and longjmp(). The
> +	  uthread_ interface enables the main thread of execution to create
> +	  one or more secondary threads and schedule them until they all have
> +	  returned. At any point a thread may suspend its execution and
> +	  schedule another thread, which allows for the efficient multiplexing
> +	  of leghthy operations.
> +
> +config UTHREAD_STACK_SIZE
> +	int "Default uthread stack size"
> +	depends on UTHREAD
> +	default 32168

Why choose 32168? It's even not a power of two. Typo for 32768?

> +	help
> +	  The default stask size for uthreads. Each uthread has its own stack.
> +
>  endmenu
>  
>  source "lib/fwu_updates/Kconfig"

Thanks,
Yao Zi