Message-ID: <2e67402b-4a32-9da9-3b06-e271c23d2422@ti.com>
Date:   Thu, 16 Nov 2017 12:32:33 -0600
From:   "Andrew F. Davis" <afd@...com>
To:     "H. Nikolaus Schaller" <hns@...delico.com>
CC:     Tomi Valkeinen <tomi.valkeinen@...com>,
        Thierry Reding <thierry.reding@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Benoît Cousson <bcousson@...libre.com>,
        Tony Lindgren <tony@...mide.com>,
        Russell King <linux@...linux.org.uk>,
        Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Julia Lawall <Julia.Lawall@...6.fr>,
        Sean Paul <seanpaul@...omium.org>,
        <dri-devel@...ts.freedesktop.org>, <devicetree@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <linux-omap@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-fbdev@...r.kernel.org>, <letux-kernel@...nphoenux.org>,
        <kernel@...a-handheld.com>
Subject: Re: [PATCH v2 1/4] omapdrm: fix compatible string for td028ttec1

On 11/16/2017 12:18 PM, H. Nikolaus Schaller wrote:
> 
>> Am 16.11.2017 um 18:08 schrieb Andrew F. Davis <afd@...com>:
>>
>> On 11/16/2017 10:10 AM, H. Nikolaus Schaller wrote:
>>> Hi Andrew,
>>>
>>>> Am 16.11.2017 um 16:53 schrieb Andrew F. Davis <afd@...com>:
>>>>
>>>> On 11/16/2017 07:43 AM, H. Nikolaus Schaller wrote:
>>>>>
>>>>>> Am 16.11.2017 um 13:32 schrieb Tomi Valkeinen <tomi.valkeinen@...com>:
>>>>>>
>>>>>> On 16/11/17 10:50, H. Nikolaus Schaller wrote:
>>>>>>> The vendor name was "toppoly" but other panels and the vendor list
>>>>>>> have defined it as "tpo". So let's fix it in driver and bindings.
>>>>>>>
>>>>>>> Signed-off-by: H. Nikolaus Schaller <hns@...delico.com>
>>>>>>> ---
>>>>>>
>>>>>>
>>>>>>> -MODULE_ALIAS("spi:toppoly,td028ttec1");
>>>>>>> +MODULE_ALIAS("spi:tpo,td028ttec1");
>>>>>>
>>>>>> Doesn't this mean that the module won't load if you have old bindings?
>>>>>
>>>>> Hm.
>>>>>
>>>>> Well, I think it can load but doesn't automatically from DT strings which might
>>>>> be unexpected.
>>>>>
>>>>>> Can't we have two module aliases?
>>>>>
>>>>> I think we can. Just a random example:
>>>>> https://elixir.free-electrons.com/linux/latest/source/drivers/w1/slaves/w1_therm.c#L754
>>>>>
>>>>> So we should keep both.
>>>>
>>>> Even better would be to drop both MODULE_ALIAS and let the
>>>> MODULE_DEVICE_TABLE macro define them for your from the SPI id table.
>>>
>>> Why would that be better?
>>>
>>
>> MODULE_ALIAS is ugly, you already have a table (usually) of device names
>> that are supported by the driver, the module aliases should be generated
>> from that table. This also keeps supported device list in one place.
>>
>>> As far as I see it will need more code and changes than adding one line of
>>> MODULE_ALIAS.
>>>
>>>> Although it doesn't look like this driver has an SPI id table, you
>>>> should probably add one, I be interested to see if this module is always
>>>> being matched through the "spi" or the "of" alias..
>>>
>>> Could you please propose how that code should look like, so that I can test?
>>>
>>
>> Sure,
>>
>> start with
>> $ udevadm monitor
>> and see what string the kernel is looking for when trying to find a
>> module for this device.
> 
> Well, the module is loaded automatically from DT at boot time well before
> I can start udevadm. So that is the most tricky part to setup the system
> to suppress this...
> 
>>
>> If it is only ever looking for "of:toppoly,td028ttec1", then you can
>> drop the MODULE_ALIAS and be done as it was never getting used anyway.
> 
> Since it is an SPI client, I am sure it looks for "spi:something.
> 
>>
>> What I expect though is "spi:toppoly,td028ttec1", in which case you
>> should add
>>
>> static const struct spi_device_id td028ttec1_ids[] = {
>> 	{ "toppoly,td028ttec1", 0 },
>> 	{ "tpo,td028ttec1", 0},
>> 	{ /* sentinel */ }
>> };
>> MODULE_DEVICE_TABLE(spi, td028ttec1_ids);
> 
> We already have a static const struct of_device_id td028ttec1_of_match[]
> table with the same information.
> 
> So we still have two places to keep in sync.
> 
> Or can we remove the td028ttec1_of_match[]? AFAIK not.
> 
>>
>> link to it in the td028ttec1_spi_driver struct:
>> .id_table = td028ttec1_ids,
>>
>> Then test again to see that the module still loads with the new and old
>> DT string.
> 
> In total I am not really convinced that adding 7 lines of code is better
> than one (the "tpo," alias) that is tested and works...
> 
> And it looks like a lot of unplanned code testing for me which takes more
> than 5 minutes :)
> 
> So I'd prefer to leave that exercise of fixing the MODULE_ALIAS/DEVICE_TABLE
> to someone else...
> 

That's fine, someday I'll probably get some script to do this for all
the drivers that still have MODULE_ALIAS and an existing table.

> BR and thanks,
> Nikolaus
> 
>>
>> Andrew
>>
>>> BR and thanks,
>>> Nikolaus Schaller
>>>
>>>>
>>>>>
>>>>> Should I submit a new version?
>>>>>
>>>>> BR,
>>>>> Nikolaus
>>>>>
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