linux-kernel - Re: [PATCH RFT 3/3] ARM: tegra: dts: seaboard: enable keyboard

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Date:	Mon, 14 Jan 2013 16:55:51 +0000
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Stephen Warren <swarren@...dotorg.org>
Cc:	Laxman Dewangan <ldewangan@...dia.com>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH RFT 3/3] ARM: tegra: dts: seaboard: enable keyboard

On Mon, Jan 14, 2013 at 09:45:52AM -0700, Stephen Warren wrote:
> On 01/12/2013 03:34 AM, Laxman Dewangan wrote:
> ...
> > Which is the tree on which Prashant changes are applied. I can debug
> > from that tree.
> 
> git://nv-tegra.nvidia.com/user/swarren/linux-2.6 test-ccf-rework-v4
> 
> But as I said in some other email in response to Prashant, I'll go and
> find out why the clk driver is returning NULL.

Exactly - the rule is, the rest of the clk API should accept as valid
anything which clk_get() produces _for that implementation_ which
IS_ERR() is not equal to 1.

What that means is:
- if a platform's clk_get() never returns NULL, then the rest of the clk
  API need not test for that value.

  (If a NULL pointer is passed to one of the clk API functions, crashing
  _is_ _okay_.  Consider what memset(NULL, 0, 4096) would do from the
  kernel - it doesn't test for a NULL pointer just because it can - it
  crashes so you can debug why it was passed a NULL pointer.)

- if a platform's clk_get() does return NULL, then the rest of the clk
  API is expected to deal with a NULL pointer in a way that does _not_
  result in the system crashing.

Or, to put it another way:

	clk = clk_get(...);
	if (IS_ERR(clk))
		return PTR_ERR(clk);

	clk_foo(clk);

for all possible return values of clk_get() that an implementation
_actually_ _intentionally_ returns[*] should never cause an oops.

[*] - bugs excluded.  No bugs were squashed in the creation of this email.
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