Message-Id: <D565D101-4EAF-4B3C-907F-A826EF53B5AF@goldelico.com>
Date:   Thu, 16 Nov 2017 19:56:54 +0100
From:   "H. Nikolaus Schaller" <hns@...delico.com>
To:     "Andrew F. Davis" <afd@...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

Hi Andrew,

> Am 16.11.2017 um 19:32 schrieb Andrew F. Davis <afd@...com>:
> 
> 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.

That would be cool!

On a second thought, I think there is a quick experiment for this driver
not needing to monitor events.

1st attempt: remove ALIASES => if it still loads it would be fine
2nd attempt: add your id table => if it loads again, it is fine
if not, let's keep ALIASES.

Maybe I can try tomorrow.

BR and thanks,
Nikolaus

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