linux-kernel - Re: [PATCH v2 1/4] omapdrm: fix compatible string for td028ttec1

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Message-Id: <689D4636-A169-4C4A-89C2-7039C78E853F@goldelico.com>
Date:   Thu, 16 Nov 2017 19:18:19 +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


> 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...

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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