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

[Hans de Goede]

Hi,

On 17-06-17 01:38, Darren Hart wrote:
> On Fri, Jun 16, 2017 at 03:22:45PM +0200, Hans de Goede wrote:
> > Hi,
> >
> > On 16-06-17 14:44, Andy Shevchenko wrote:
> > > On Thu, Jun 15, 2017 at 7:53 PM, Darren Hart <dvhart@xxxxxxxxxxxxx> 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.
>
> Do we have any indication that this BIOS Date isn't just the default value
> provided by AMI?

In my experience with devices with similar generic DMI strings,
the BIOS date is different for all of them, I believe the
tools use to build the BIOS set this to the actual build date.

> Does it offer any more information than the BIOS Version?

Yes it does a web search for "3BAIR1013" finds unrelated matches,
so that alone is not enough, where as the BIOS date tends to be
unique.

> I suppose we may be able to do some kind of a partial match on the Board Serial
> if even that is platform specific (I suspect it is with the T800 at the
> beginning.
>
> The sloppy handling of this firmware really irks me. That's obviously not Hans'
> fault, so we'll take the patch.

Thank you.

Regards,

Hans