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SubjectRe: [PATCH 09/23] clocksource: add block notifier

* Daniel Walker <dwalker@mvista.com> wrote:

> Adds a call back interface for register/rating change events. This is
> also used later in this series to signal other interesting events.

This patch adds:

> +#define CLOCKSOURCE_NOTIFY_REGISTER 1
> +#define CLOCKSOURCE_NOTIFY_RATING 2
> +#define CLOCKSOURCE_NOTIFY_FREQ 4

and a later patch adds:

> +#define CLOCKSOURCE_NOTIFY_UNSTABLE 8

while i tentatively agree with the introduction of clocksource driver
notifications in general (given any actual real users of that
infrastructure), i can see three problems with your notifier changes:

firstly, with the full changes applied, CLOCKSOURCE_NOTIFY_RATING is
totally unused (and not even driven by the core clocksource code).

secondly, CLOCKSOURCE_NOTIFY_REGISTER is only used by the core
clocksource code and no register-notifier interface is exposed: this
makes the whole thing an expensive NOP.

thirdly, CLOCKSOURCE_NOTIFY_FREQ is totally unused as well.

(there are tons of examples in the kernel of how to do driver
notification APIs properly.)

Ingo
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