Re: [PATCH 13/18] iio: adc: mcp320x: Set struct spi_driver .of_match_table

From: Javier Martinez Canillas <javier@osg.samsung.com>
To: Rob Herring <robherring2@gmail.com>, Jonathan Cameron <jic23@kernel.org>
Cc: "Michael Welling" <mwelling@ieee.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
	"Andrea Galbusera" <gizero@gmail.com>,
	"linux-iio@vger.kernel.org" <linux-iio@vger.kernel.org>,
	"Peter Meerwald" <pmeerw@pmeerw.net>,
	"Lars-Peter Clausen" <lars@metafoo.de>,
	"Manfred Schlaegl" <manfred.schlaegl@gmx.at>,
	"Søren Andersen" <san@rosetechnology.dk>,
	"Hartmut Knaack" <knaack.h@gmx.de>,
	"devicetree@vger.kernel.org" <devicetree@vger.kernel.org>
Subject: Re: [PATCH 13/18] iio: adc: mcp320x: Set struct spi_driver .of_match_table
Date: Mon, 24 Aug 2015 09:19:24 +0200	[thread overview]
Message-ID: <55DAC57C.9020502@osg.samsung.com> (raw)
In-Reply-To: <CAL_Jsq+_ET8O=vQirFutY5sF7rkK-qF_1uTAroto2dZzC4ugWA@mail.gmail.com>

Hello Rob and Jonathan,

On 08/24/2015 12:10 AM, Rob Herring wrote:
> On Sat, Aug 22, 2015 at 12:48 PM, Jonathan Cameron <jic23@kernel.org> wrote:
>> On 20/08/15 23:48, 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.
>> Take the view the old version is wrong but needs to be supported and add also
>> the corrected strings + document them.
>>
>> cc'd The device tree list for any more comments on this.
> 
> Agreed. Document both and mark the old one deprecated.
>

Thanks a lot for your comments. I'll do that as a follow up then.

> Rob
> 

Best regards,
-- 
Javier Martinez Canillas
Open Source Group
Samsung Research America