[RFC] Barebox shutdown hooks

[Sascha Hauer]

Hi Herve,

On Fri, Jun 12, 2015 at 11:41:25AM +0200, Herve Codina wrote:
> I try to find a way to perform some tasks on barebox leaving (ie last step of go command or boot/bootm command)
> and i look at shutdown_barebox (common/startup.c)
> This function is :
> ---- 8< -----
> void shutdown_barebox(void)
> {
> 	devices_shutdown();
> #ifdef ARCH_SHUTDOWN
> 	arch_shutdown();
> #endif
> 	if (board_shutdown)
> 		board_shutdown();
> }
> ---- 8< -----
> 
> I have several questions :
> 
> 1) Why board_shutdown is called after arch_shutdown.
> arch shutdown is supposed to do stuf like disabling mmu, flushing cache, ...
> Don't you think that board_shutdown should be between devices_shutdown and arch_shutdown ?

You are probably right. Only one single board implements board_shutdown
anyway, so I guess it's just where it suited the original author.

> 
> 2) What about the ability to have hooks for shutdown with all resources available
> For my tasks, i need devices available. What do you thing about a new "early_shutdown" called before devices_shutdown.
> barebox_shutdown will become :
> void shutdown_barebox(void)
> {
> 	early_shutdown();
> 	devices_shutdown();
> #ifdef ARCH_SHUTDOWN
> 	arch_shutdown();
> #endif
> 	if (board_shutdown)
> 		board_shutdown();
> }
> 
> for early_shutdown itself, i would give flexibility. I thing about 2 way :
> 
> 2.1) register shutdown hooks
> Use same mechanism as fixing up device tree :
> early_shutdown_register function to register hook
> and iterator calling all registered hooks in early_shutdown
> 
> 2.2) exitcall
> Use same mechanism as initcall functions :
> Use a specific section to store exit hooks table. A macro early_exitcall (same mechanism as xxxx_initcall macro) will be used to do this.
> Iterate on each hook in this section in early_shutdown (same mechanism as initcall in start_barebox).

I vote for 2.2). It has the smaller runtime overhead and we can hook
the existing devices_shutdown, arch_shutdown and board_shutdown into
that mechanism aswell.

Sascha

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