linux-kernel - Re: [PATCH v7 08/24] mfd: max77686: Add Dynamic Voltage Scaling (DVS) support

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Message-ID: <53BFB957.7010307@collabora.co.uk>
Date:	Fri, 11 Jul 2014 12:15:51 +0200
From:	Javier Martinez Canillas <javier.martinez@...labora.co.uk>
To:	Tomasz Figa <t.figa@...sung.com>,
	amit daniel kachhap <amit.daniel@...sung.com>
CC:	Lee Jones <lee.jones@...aro.org>,
	Alessandro Zummo <a.zummo@...ertech.it>,
	Krzysztof Kozlowski <k.kozlowski@...sung.com>,
	Kukjin Kim <kgene.kim@...sung.com>,
	Mike Turquette <mturquette@...aro.org>,
	Tomeu Vizoso <tomeu.vizoso@...labora.com>,
	devicetree@...r.kernel.org,
	Yadwinder Singh Brar <yadi.brar01@...il.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Liam Girdwood <lgirdwood@...il.com>,
	Doug Anderson <dianders@...omium.org>,
	Tushar Behera <trblinux@...il.com>,
	Mark Brown <broonie@...nel.org>,
	"linux-samsung-soc@...r.kernel.org" 
	<linux-samsung-soc@...r.kernel.org>,
	Olof Johansson <olof@...om.net>,
	Andreas Farber <afaerber@...e.de>,
	LAK <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 08/24] mfd: max77686: Add Dynamic Voltage Scaling (DVS)
 support

Hello Tomasz,

On 07/11/2014 11:43 AM, Tomasz Figa wrote:
> Hi Javier,
> 
> On 11.07.2014 03:45, Javier Martinez Canillas wrote:
>> On 07/10/2014 11:59 AM, amit daniel kachhap wrote:
>>> On Sat, Jul 5, 2014 at 1:54 AM, Javier Martinez Canillas
>>> <javier.martinez@...labora.co.uk> wrote:
> 
> [snip]
> 
>>>> @@ -111,6 +223,13 @@ static struct max77686_platform_data *max77686_i2c_parse_dt_pdata(struct device
>>>>                 return NULL;
>>>>
>>>>         dev->platform_data = pd;
>>>> +
>>>> +       /* Read default index and ignore errors, since default is 0 */
>>>> +       of_property_read_u32(np, "max77686,pmic-buck-default-dvs-idx",
>>>> +                            &pd->buck_default_idx);
>>> Any error checking code here. Say if pmic-buck-default-dvs-idx exceed 8?
>> 
>> I'm not a DT expert but AFAIK the kernel should expect the data in a FDT to be
>> correct and should not validate it on runtime. There is work-in-progress to add
>> a proper schema checking for DTS to the dtc so on build time it can be validated
>> that a DTS is valid.
>> 
>> AFAIU the only thing that the kernel should check is if a required property does
>> not exist.
> 
> I'd disagree on this.
> 
> IMHO schema (if it progresses further, as unfortunately I can't find
> time to dedicate to it and looks like it's similar for other people that
> used to be involved) should be focused on structural checks, i.e. proper
> layout of nodes and properties, basic data types and so, to figure out
> common errors earlier than at boot-up time.
> 
> On kernel side this should be treated in the same way as platform data.
> I agree that some existing drivers do little to validate incoming data,
> but I believe it is a good practice to validate things that the driver
> has no control over, especially when it's about a PMIC, when invalid
> data can have quite serious effects and detecting even some of them
> (e.g. value to big, which would overflow in target bit field) might
> prevent a failure.
> 

Thanks a lot for the clarification and I completely agree with your explanation.
I'll add proper validation for the data obtained by DT then. It would be nice if
this was documented somewhere (or maybe I missed it).

> Best regards,
> Tomasz
> 

Best regards,
Javier
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