Date:   Thu, 2 Feb 2017 06:47:12 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:     Javier Martinez Canillas <javier@....samsung.com>,
        Mark Rutland <mark.rutland@....com>,
        Michel Verlaan <michel.verl@...il.com>,
        Nick Dyer <nick@...anahar.org>,
        Tony Lindgren <tony@...mide.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Benjamin Tissoires <benjamin.tissoires@...hat.com>,
        linux-omap <linux-omap@...r.kernel.org>,
        Russell King <linux@...linux.org.uk>,
        Igor Grinberg <grinberg@...pulab.co.il>,
        Hans Verkuil <hans.verkuil@...co.com>,
        linux-input@...r.kernel.org,
        devicetree <devicetree@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Eric Engestrom <eric@...estrom.ch>,
        Hans de Goede <hdegoede@...hat.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mika Penttilä <mika.penttila@...tfour.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Petr Cvek <petr.cvek@....cz>,
        Siebren Vroegindeweij <siebren.vroegindeweij@...mail.com>,
        Sebastian Reichel <sre@...nel.org>, linux-iio@...r.kernel.org,
        "Andrew F. Davis" <afd@...com>, Mark Brown <broonie@...nel.org>,
        Benoît Cousson <bcousson@...libre.com>,
        kernel@...a-handheld.com, Michael Welling <mwelling@...e.org>,
        Jonathan Cameron <jic23@...nel.org>,
        Alexander Stein <alexander.stein@...tec-electronic.com>,
        Discussions about the Letux Kernel 
        <letux-kernel@...nphoenux.org>
Subject: Re: [PATCH v9 6/8] drivers:input:ads7846(+tsc2046): fix spi module table

Hi,

> Am 01.02.2017 um 23:28 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
> 
> On Wed, Feb 01, 2017 at 06:14:39PM -0300, Javier Martinez Canillas wrote:
>> Hello Nikolaus,
>> 
>> On 02/01/2017 05:20 PM, H. Nikolaus Schaller wrote:
>>> Hi Dmitry, Javier,
>>> 
>>>> Am 29.01.2017 um 19:25 schrieb H. Nikolaus Schaller <hns@...delico.com>:
>>>> 
>>>> Hi Dmitry,
>>>> 
>>>>> Am 29.01.2017 um 19:01 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
>>>>> 
>>>>> On Sun, Jan 29, 2017 at 09:39:39AM +0100, H. Nikolaus Schaller wrote:
>>>>>> Hi Dmitry,
>>>>>> 
>>>>>>> Am 28.01.2017 um 20:35 schrieb Dmitry Torokhov <dmitry.torokhov@...il.com>:
>>>>>>> 
>>>>>>> On Wed, Dec 28, 2016 at 03:53:21PM +0100, H. Nikolaus Schaller wrote:
>>>>>>>> Fix module table so that the driver is loaded if compiled
>>>>>>>> as module and requested by DT.
>>>>>>>> 
>>>>>>> 
>>>>>>> I believe I already replied to a similar patch: we alreadyhave necessary
>>>>>>> aliases in this driver, we need to fix module loading to use it.
>>>>>> 
>>>>>> Yes, you did comment on [PATCH v6 7/8] (19 Nov 2016):
>>>>>> 
>>>>>>>> We really need to fix it between spi/i23c core and module utils instead
>>>>>>>> of keeping adding duplicate IDs all over drivers. We already have OF
>>>>>>>> module device table containing the same data, we should be able to use
>>>>>>>> it.
>>>>>> 
>>>>>> And Javier Martinez Canillas replied (23 Nov 2016):
>>>>>> 
>>>>>>> Agreed, unfortunately until the I2C and SPI core are changed to properly
>>>>>>> report OF modaliases, we will have to keep adding these duplicated IDs.
>>>>>>> 
>>>>>>> And changing the I2C and SPI core isn't trivial since it could break a
>>>>>>> lot of drivers that rely on a platform modalias being reported (i.e: no
>>>>>>> OF device IDs present in the drivers even when are registered via DT).
>>>>>> 
>>>>>> Therefore I didn't see a need to change it.
>>>>> 
>>>>> I agree that changing I2C and SPI core is not trivial, however this is
>>>>> no reason for piling up workarounds in all drivers. Are you seriously
>>>>> advocating going though *every* driver and copying OF data into I2C/SPI
>>>>> instead of doing the right thing and fixing the root of the issue?
>>>> 
>>>> If you prefer to have this done (and I agree it would be a tiny improvement),
>>>> please do it for us all. But please after merging this workaround.
>>> 
>>> Have we been lucky to find someone who is able and willing to work on this?
>>> 
>> 
>> As said, changing the core is trivial. A RFC patch is [0].
>> 
>> The problem is how to make sure that this change won't cause regressions
>> in existing drivers.
> 
> If the concern with drivers having I2C or SPI device table, but not OF
> device table, then I think cocinnelle could be used to scan and find
> them.
> 
>> 
>> There was particularly tricky for the spi-nor driver, it doesn't help that
>> a lot of DT are using undocumented compatible strings (sometimes with no
>> vendor prefix). You can see the discussion here [1].
>> 
>> In the same thread Mark Brown said that it wasn't that bad to have the
>> information in the OF device ID table duplicated in a SPI device table.
>> 
>> Certainly isn't the best approach but IMHO is better than the module not
>> loading.
> 
> You can always build the module into kernel or load it by hand if it is
> that important.

Well, it is the only exception on the OpenPandora that does NOT yet load
automatically from the DT.

And sure we can always find a hack or workaround in user-space for everything
the kernel isn't doing well.

> Module autoloading does not work anyway if you have
> several compatible strings, like
> 
> 	compatible = "vendor,new-device", "vendor,generic-device";

We don't use that mechanism here since there is only one ads7846 installed
and it won't change.

BR,
Nikolaus

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