Message-ID: <4F693DD8.7070305@codeaurora.org>
Date:	Tue, 20 Mar 2012 19:32:56 -0700
From:	Saravana Kannan <skannan@...eaurora.org>
To:	"Turquette, Mike" <mturquette@...com>
CC:	Sascha Hauer <s.hauer@...gutronix.de>,
	Andrew Lunn <andrew@...n.ch>,
	Grant Likely <grant.likely@...retlab.ca>,
	Jamie Iles <jamie@...ieiles.com>,
	Jeremy Kerr <jeremy.kerr@...onical.com>,
	Magnus Damm <magnus.damm@...il.com>,
	Deepak Saxena <dsaxena@...aro.org>,
	linux-arm-kernel@...ts.infradead.org,
	Arnd Bergman <arnd.bergmann@...aro.org>,
	linux-arm-msm@...r.kernel.org,
	Rob Herring <rob.herring@...xeda.com>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Richard Zhao <richard.zhao@...aro.org>,
	Shawn Guo <shawn.guo@...escale.com>,
	Paul Walmsley <paul@...an.com>,
	Linus Walleij <linus.walleij@...ricsson.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Stephen Boyd <sboyd@...eaurora.org>,
	linux-kernel@...r.kernel.org,
	Amit Kucheria <amit.kucheria@...aro.org>
Subject: Re: [PATCH 1/2] clk: Fix error handling in fixed clock hardware type
 register fn

On 03/20/2012 05:13 PM, Turquette, Mike wrote:
> On Tue, Mar 20, 2012 at 12:46 AM, Saravana Kannan
> <skannan@...eaurora.org>  wrote:
>> On Tue, March 20, 2012 12:19 am, Sascha Hauer wrote:
>>> On Mon, Mar 19, 2012 at 08:38:25PM -0700, Saravana Kannan wrote:
>>>> If memory allocation for the parents array or the parent string fails,
>>>> then
>>>> fail the registration immediately instead of calling clk_register and
>>>> hoping it fails there.
>>>>
>>>> Return -ENOMEM on failure.
>>>>
>>>> Signed-off-by: Saravana Kannan<skannan@...eaurora.org>
>>>> Cc: Mike Turquette<mturquette@...aro.org>
>>>> Cc: Andrew Lunn<andrew@...n.ch>
>>>> Cc: Rob Herring<rob.herring@...xeda.com>
>>>> Cc: Russell King<linux@....linux.org.uk>
>>>> Cc: Jeremy Kerr<jeremy.kerr@...onical.com>
>>>> Cc: Thomas Gleixner<tglx@...utronix.de>
>>>> Cc: Arnd Bergman<arnd.bergmann@...aro.org>
>>>> Cc: Paul Walmsley<paul@...an.com>
>>>> Cc: Shawn Guo<shawn.guo@...escale.com>
>>>> Cc: Sascha Hauer<s.hauer@...gutronix.de>
>>>> Cc: Jamie Iles<jamie@...ieiles.com>
>>>> Cc: Richard Zhao<richard.zhao@...aro.org>
>>>> Cc: Saravana Kannan<skannan@...eaurora.org>
>>>> Cc: Magnus Damm<magnus.damm@...il.com>
>>>> Cc: Mark Brown<broonie@...nsource.wolfsonmicro.com>
>>>> Cc: Linus Walleij<linus.walleij@...ricsson.com>
>>>> Cc: Stephen Boyd<sboyd@...eaurora.org>
>>>> Cc: Amit Kucheria<amit.kucheria@...aro.org>
>>>> Cc: Deepak Saxena<dsaxena@...aro.org>
>>>> Cc: Grant Likely<grant.likely@...retlab.ca>
>>>> ---
>>>> There are still some memory free issues when clk_register() fails, but I
>>>> will
>>>> fix it when I fixed the other register() fns to return ENOMEM of alloc
>>>> failure instead of a NULL.
>>>>
>>>>   drivers/clk/clk-fixed-rate.c |   10 +++++++---
>>>>   1 files changed, 7 insertions(+), 3 deletions(-)
>>>>
>>>> diff --git a/drivers/clk/clk-fixed-rate.c b/drivers/clk/clk-fixed-rate.c
>>>> index 90c79fb..6423ae9 100644
>>>> --- a/drivers/clk/clk-fixed-rate.c
>>>> +++ b/drivers/clk/clk-fixed-rate.c
>>>> @@ -61,22 +61,26 @@ struct clk *clk_register_fixed_rate(struct device
>>>> *dev, const char *name,
>>>>               parent_names = kmalloc(sizeof(char *), GFP_KERNEL);
>>>>
>>>>               if (! parent_names)
>>>> -                    goto out;
>>>> +                    goto fail_ptr;
>>>>
>>>>               len = sizeof(char) * strlen(parent_name);
>>>>
>>>>               parent_names[0] = kmalloc(len, GFP_KERNEL);
>>>>
>>>>               if (!parent_names[0])
>>>> -                    goto out;
>>>> +                    goto fail_str;
>>>>
>>>>               strncpy(parent_names[0], parent_name, len);
>>>>       }
>>>
>>> It's easier to add a char *parent to struct clk_fixed and pass it to
>>> clk_register with&fixed->parent. This saves you a kmalloc call and
>>> makes the error path simpler. It's the same way already done in the
>>> divider.
>
> I thought I had done this for v7... hmm looks like one got left out.
> I'll line up a patch to get it in sync with the others as part of my
> fixes.
>
>> I thought about that since I saw the same was done for gated and divider
>> (I think). Here is my guess at Mike's reasoning for this:
>>
>> Gated and divider clocks have to have a parent. There's nothing to gate
>> otherwise. But fixed rate clocks might not have a parent. It could be XO's
>> or PLLs running off of always on XOs not controlled by the SoC. So, it's
>> arguable to not have a parent. I don't have a strong opinion on this --
>> since Mike took the time to write it, it left it to his subjective
>> preference.
>
> I appreciate the thoughtfulness.  Re-using the same type of mechanism
> as the divider and gate clocks will still allow the fixed-rate clock
> to be parentless, and it makes for cleaner code, one less allocation
> and lines up with how the other single-parent basic clocks are done,
> so I'll take that method in instead of your patch.

No problem, go for it.

>
>> I sent this patch first since it was around the place I was cleaning up. I
>> didn't want to actually just shuffle around a bug. As I mentioned, this
>> patch still leaves a bug open -- what if clk_register() fails. I plan to
>> fix that once my two patches are picked up (hopefully).
>
> Do you still find it useful to return -ENOMEM from the registration
> function instead of a NULL clock?  I'm always worried that people
> don't check for error codes on pointers in their platform code and
> only check for NULL...

The last discussion I remember, NULL was considered a valid clock. So, I 
think on error, we shouldn't ever return NULL when the return type is 
struct clk *.

Thanks,
Saravana

-- 
Sent by an employee of the Qualcomm Innovation Center, Inc.
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum.
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