linux-kernel - Re: [PATCH 1/2] User access to internal clocks

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Date:	Mon, 9 Feb 2009 19:17:07 +0100
From:	Davide Rizzo <elpa.rizzo@...il.com>
To:	Russell King - ARM Linux <linux@....linux.org.uk>
Cc:	gregkh@...e.de, linux-kernel@...r.kernel.org, ben-linux@...ff.org,
	linux-api@...r.kernel.org
Subject: Re: [PATCH 1/2] User access to internal clocks

> You're not understanding the issue(s).
>
> 1. there is no 1:1 mapping between the identifiers (struct device +
>   connection ID) and the struct clk.  It's actually a many-to-one
>   mapping.
>
>   That means there is _no_ name associated with a struct clk.
>
>   Conceptually, clk_get() gives you a struct clk for the struct device
>   and a connection ID.  How that mapping is achieved isn't specified
>   in the API, all that's required is that such a mapping is performed.
>   It is _specifically_ intended that more than one set of {device,id}
>   pairs will map to the same clk.
>
>   So, now to insist that you can go from a struct clk to some kind of
>   string identifier for it is changing this - you're now requiring
>   that every struct clk has a unique name.  This is not the case.
>   PXA, for instance, struct clk's are now completely nameless.  They
>   have no identifier.
>
>   If you want to have a string identifier which works in every case,
>   this will:
>
>        sprintf(identifer, "%p", clk);
>
>   Or, I guess you could force every struct clk to have a 'sysfs_name'
>   field just to export them out via sysfs - and that'll be all that
>   it's used for.
>
> 2. there is no generic way to walk a set of struct clk's - indeed, there
>   may be no list of them (and there exists implmentations where that is
>   true) and the only list which does exist is a set ID to clk mapping
>   structures.
>
>> Otherwise, what do you suggest to enumerate and distinguish all system
>> clocks ?
>
> There exists no such concept in the API, what you're asking for is
> implementation specific.
>

Thank you for this explanation, now it's much more clear to me.

What about adding a dedicated function to clk api that registers a struct clk
 in a linked list and associates it with a name, with the only specific purpose
 to enumerate and list (and possibly change rate and parents) all
clocks in sysfs ?
Obviously only specifically registered clocks will be visible in sysfs...
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