linux-kernel - Re: [PATCH 1/9] iio: adc: exynos_adc: use regmap to retrieve struct device

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Date:	Sun, 10 Apr 2016 14:45:02 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Marek Szyprowski <m.szyprowski@...sung.com>,
	Alison Schofield <amsfield22@...il.com>
Cc:	knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
	kgene@...nel.org, k.kozlowski@...sung.com,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-samsung-soc@...r.kernel.org
Subject: Re: [PATCH 1/9] iio: adc: exynos_adc: use regmap to retrieve struct
 device

On 07/04/16 06:33, Marek Szyprowski wrote:
> Hello,
> 
> On 2016-04-06 22:33, Alison Schofield wrote:
>> On Wed, Apr 06, 2016 at 09:03:00AM +0200, Marek Szyprowski wrote:
>>> Hello,
>>>
>>> On 2016-04-06 07:15, Alison Schofield wrote:
>>>> Driver includes struct regmap and struct device in its global data.
>>>> Remove the struct device and use regmap API to retrieve device info.
>>>>
>>>> Patch created using Coccinelle plus manual edits.
>>>>
>>>> Signed-off-by: Alison Schofield <amsfield22@...il.com>
>>> This patch changes the struct device which is used by the driver to report
>>> errors. The driver used correctly the struct device associated with its
>>> device tree node, while after the patch it will use device which is
>>> associated with PMU regmap, which is a different device. PMU regmap is there
>>> only to enable/disable the ADC block and it is not the regmap used to access
>>> registers of the ADC device.
>>>
>>> I would prefer to drop this patch.
>> Thanks Marek!  Please check my understanding.  Driver is not carrying
>> a duplicate struct device. The regmap in exynos_adc is *not* this
>> devices regmap. It belongs to the PMU, (power mgmt unit?)
> 
> Exactly.
> 
>> It seemed excessive to carry around a struct device just for the
>> dev_err messages, but, we need that struct to extract the correct
>> iio_dev struct. Without a regmap belonging to this actual device,
>> no efficiencies can be gained in exynos, and the patch will be
>> dropped from set v2.
> 
> Thanks.
> 
>> Now I need to be able to recognize such cases elsewhere. I'm going
>> back though other patches in this set looking for that, but I'm not
>> so sure I would recognize it.
>>
>> Jonathan & all, Any hints on the rule of regmap?
> 
> You may check how the regmap is initialized. When it is retrieved by
> phandle from device tree, then you might be almost sure that it refers
> to the different device.
True enough.  Most simple devices that stand alone should be fine for
this sort of cleanup as the regmap is typically initiated directly for them.

Jonathan
> 
> Best regards