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

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

[Jonathan Cameron]

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.
> 
> 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.
> 
> [0]: https://www.power.org/documentation/epapr-version-1-1/
> 
> Best regards,
> 

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

[Rob Herring]

On Sat, Aug 22, 2015 at 12:48 PM, Jonathan Cameron <jic23-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.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.

Rob

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

[Javier Martinez Canillas]

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-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.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