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

From: Javier Martinez Canillas <javier@osg.samsung.com>
To: Michael Welling <mwelling@ieee.org>
Cc: linux-kernel@vger.kernel.org,
	"Andrea Galbusera" <gizero@gmail.com>,
	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>,
	"Jonathan Cameron" <jic23@kernel.org>,
	"Hartmut Knaack" <knaack.h@gmx.de>
Subject: Re: [PATCH 13/18] iio: adc: mcp320x: Set struct spi_driver .of_match_table
Date: Fri, 21 Aug 2015 00:02:40 +0200	[thread overview]
Message-ID: <55D64E80.4050502@osg.samsung.com> (raw)
In-Reply-To: <20150820200912.GA2866@deathstar>

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).

> 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.

[0]: https://lkml.org/lkml/2015/8/20/109

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