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

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Date:   Thu, 16 Nov 2017 11:08:30 -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 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.

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.

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);

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.

Andrew

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