Re: [RESEND PATCH v7 2/2] mmc: OCTEON: Add host driver for OCTEON MMC controller

[Arnd Bergmann <arnd@arndb.de>]

On Wednesday 20 April 2016 01:57:08 Arnd Bergmann wrote:
> If you do this
> 
>         wait_event(&host->wq, !host->current_req);
> 
> in the request function as well as 
> 
>         wake_up(&host->wq);
> 
> after setting host->current_req to NULL, I think you end up with
> the same level of readability as the semaphore, and slightly
> better object code, and you can drop the 'WARN_ON(host->current_req);'
> which would be known to be impossible.
> 

Correction: you would still need some form of serialization to
ensure that only one thread can set the host->current_req
at any time, so it's slightly more complex, either using
a mutex around the wait_event/assignment, or doing

	wait_event(&host->wq, !cmpxchg(host->current_req, NULL, mrq));

which probably wants to be encapsulated in an inline function
or annotated with a comment.

	Arnd