linux-kernel - Re: [PATCH 13/18] iio: adc: mcp320x: Set struct spi_driver .of_match

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Date:	Sat, 22 Aug 2015 19:09:25 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Michael Welling <mwelling@...e.org>,
	Javier Martinez Canillas <javier@....samsung.com>
Cc:	linux-kernel@...r.kernel.org, Andrea Galbusera <gizero@...il.com>,
	linux-iio@...r.kernel.org, Peter Meerwald <pmeerw@...erw.net>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Manfred Schlaegl <manfred.schlaegl@....at>,
	Søren Andersen <san@...etechnology.dk>,
	Hartmut Knaack <knaack.h@....de>
Subject: Re: [PATCH 13/18] iio: adc: mcp320x: Set struct spi_driver
 .of_match_table

On 21/08/15 00:53, Michael Welling wrote:
> On Fri, Aug 21, 2015 at 12:48:23AM +0200, Javier Martinez Canillas wrote:
>> Hello Michael,
>>
>> On 08/21/2015 12:29 AM, Michael Welling wrote:
>>> On Fri, Aug 21, 2015 at 12:02:40AM +0200, Javier Martinez Canillas wrote:
>>>> Hello Michael,
>>>>
>>>> On 08/20/2015 10:09 PM, Michael Welling wrote:
>>>>> On Thu, Aug 20, 2015 at 09:07:26AM +0200, Javier Martinez Canillas wrote:
>>>>>> The driver has an OF id table but the .of_match_table is not set so
>>>>>> the SPI core can't do an OF style match and the table was unused.
>>>>>>
>>>>>
>>>>> Is an OF style match necessary?
>>>>>
>>>>
>>>> Did you read the cover letter [0] on which I explain why is needed to
>>>> avoid breaking module autoloading in the future? Once the SPI core is
>>>> changed by RFC patch 18/18? (you were cc'ed in the cover letter BTW).
>>>
>>> Well I have read it now. :)
>>>
>>
>> Great :)
>>  
>>>>
>>>>> I have been using devicetree and it matches based on the .id_table.
>>>>>
>>>>
>>>> Yes it fallbacks to the .id_table or the driver name but the correct
>>>> thing to do for devices registered by OF, is to match using the
>>>> compatible string.
>>>>
>>>>> Couldn't we just remove the mcp320x_dt_ids table instead?
>>>>>
>>>>
>>>> No, that is the wrong thing to do IMHO since the compatible string
>>>> contains both vendor and device name whle the .id_table only contains
>>>> a device name.
>>>>
>>>> So it makes sense to match using the compatible string and also report
>>>> the OF modalias information to user-space.
>>>>
>>>> Otherwise what's the point of the vendor in the compatible string for
>>>> SPI devices? You can just use "bar" instead of "foo,bar" as a string.
>>>>
>>>
>>> Well then shouldn't the patch include adding the vendor to the compatible
>>> string?
>>>
>>
>> Well, I was talking in general. You are right that this specific driver does
>> not have a vendor prefix for the compatible strings. This is incorrect
>> according to the ePAPR document [0].
>>
>> However, these compatible strings are already documented as a DT binding doc
>> in Documentation/devicetree/bindings/iio/adc/mcp320x.txt so I don't know
>> what is the correct thing to do in this situation.
>>
>> Changing the compatible string will break old DTB with newer kernels and that
>> is a no go. But that doesn't invalidate what I said since once the SPI core
>> is changed and report OF modalias, you will need a MODULE_DEVICE_TABLE(of,...)
>> regardless if the compatible string has a vendor prefix or not.
>>
> 
> Okay.
> 
> Acked-by: Michael Welling <mwelling@...e.org>
Applied to the togreg branch of iio.git

Thanks,

Jonathan
>  
>> [0]: https://www.power.org/documentation/epapr-version-1-1/
>>
>> Best regards,
>> -- 
>> Javier Martinez Canillas
>> Open Source Group
>> Samsung Research America
> --
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