linux-kernel - Re: [PATCH 1/2] platform/x86: silead_dmi: Add touchscreen info for PoV mobii wintab p800w

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Date:   Fri, 16 Jun 2017 15:22:45 +0200
From:   Hans de Goede <hdegoede@...hat.com>
To:     Andy Shevchenko <andy.shevchenko@...il.com>,
        Darren Hart <dvhart@...radead.org>
Cc:     Andy Shevchenko <andy@...radead.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] platform/x86: silead_dmi: Add touchscreen info for
 PoV mobii wintab p800w

Hi,

On 16-06-17 14:44, Andy Shevchenko wrote:
> On Thu, Jun 15, 2017 at 7:53 PM, Darren Hart <dvhart@...radead.org> wrote:
>> On Thu, Jun 15, 2017 at 08:48:31AM +0200, Hans de Goede wrote:
> 
>>> +             /* Point of View mobii wintab p800w */
>>> +             .driver_data = (void *)&pov_mobii_wintab_p800w_data,
>>> +             .matches = {
>>> +                     DMI_MATCH(DMI_BOARD_VENDOR, "AMI Corporation"),
>>> +                     DMI_MATCH(DMI_BOARD_NAME, "Aptio CRB"),
>>> +                     DMI_MATCH(DMI_BIOS_VERSION, "3BAIR1013"),
>>> +                     /* Above matches are too generic, add bios-date match */
>>> +                     DMI_MATCH(DMI_BIOS_DATE, "08/22/2014"),
>>
>> This is the first time I've seen a BIOS date match used to determine hardware
>> features. DMI matching is a (necessary) hack to begin with (the vendors should
>> be providing this data via ACPI _DSD anyway) but a date match means we would
>> need a kernel patch every time one of these tablets gets a BIOS update...
>>
>> With words like "Aptio CRB" it's clear the vendor isn't doing their job and just
>> using unmodified reference code. The problem with this of course is that the
>> vendor is not providing a way to identify this hardware.
>>
>> Andy, I'd appreciate your thoughts on this... I'm leaning towards not accepting
>> bios date (or indeed, BIOS version) as a way to identify a platform.
> 
> The question is what is the anticipated amount of affected devices
> with BIOS date included and otherwise?

I expect there to be collisions (false positive matches) without the
BIOS_DATE check, a quick web-search finds other devices with a
3BAIR1013 bios version. Those don't necessarily also use a Silead
touchscreen (which is needed for a collision to happen), but given
the popularity of Silead touchscreens on cheap devices a collision
is not unlikely.

With the bios-date check added, I expect this match to be unique,
for it to not be unique we would need to be really unlucky.

> If Hans believes that there will be no update for some devices,

Yeah I'm pretty sure this specific device will not see any
BIOS updates ever.

> while there are devices with the same DMI strings, but different date and
> _fixed_ issue, I think we have no other choice for now.
> Also can we use some other strings to distinguish group of devices
> which are affected?

bios_date: 08/22/2014
bios_vendor: American Megatrends Inc.
bios_version: 3BAIR1013
board_asset_tag: To be filled by O.E.M.
board_name: Aptio CRB
board_serial: T80091A4C11B0848
board_vendor: AMI Corporation
board_version: To be filled by O.E.M.
chassis_asset_tag: To Be Filled By O.E.M.
chassis_serial: To Be Filled By O.E.M.
chassis_type: 3
chassis_vendor: To Be Filled By O.E.M.
chassis_version: To Be Filled By O.E.M.
product_name: To be filled by O.E.M.
product_serial: To be filled by O.E.M.
product_uuid: 03000200-0400-0500-0006-000700080009
product_version: To be filled by O.E.M.
sys_vendor: To be filled by O.E.M.

The product-uuid is a known example uuid, so is
no good. The board_serial might be useful, but
only if it is unique for the model and not per
tablet. Unfortunately I only have 1 of these
tablets, so I cannot tell.

Regards,

Hans