On Wed, Dec 02, 2020 at 02:48:47PM +0200, Laurent Pinchart wrote: > On Tue, Dec 01, 2020 at 09:34:58PM +0100, Hans de Goede wrote: > > On 12/1/20 8:21 PM, Andy Shevchenko wrote: > > > On Tue, Dec 01, 2020 at 09:06:38PM +0200, Laurent Pinchart wrote: ... > > > I would rather ask Hans' opinion since he has quite an expertise with DMI for > > > good and bad. > > > > So generally there are 2 ways how things like this can go: > > > > 1) There is sufficient information in the ACPI table and we use data from the > > ACPI tables > > > > 2) There is unsufficient info in the ACPI tables (or we don't know how to > > get / interpret the data) and we use DMI quirks > > And this specific case I believe there is sufficient data in the ACPI > tables, as I don't believe the Windows driver uses DMI quirks, or comes > in the form of machine-specific binaries. We however don't know how to > interpret all the data, but that should hopefully get better over time > (especially as we'll get more data points, with ACPI dumps from machines > whose schematics have leaked). I think you are too optimistic about this part of Windows drivers. I would rather think about hardware stuck with the same frequencies which simply are hard coded in the Windows driver. I have description of ASL for this camera, but I don't see anything like this you are describing. > > Although we do often also use a combination, getting what we can from ACPI, > > combined with a set of defaults for what we cannot get from ACPI > > based on what reference designs use (IOW what most devices seem to have > > copy and pasted). Combined with DMI quirks for when the defaults do not > > work (which is quite often). > > > > Depending on if "not working because of wrong defaults" has bad side effects, > > another option is also to only allow the driver to load on devices which > > have the necessary info provided through a DMI match. > > Right now there shouldn't be bad side effects, but in the future we'll > need to setup a PMIC whose output voltages can be controlled, and > getting it wrong would be very bad. For that I'll definitely vote for > DMI match to start with, but I don't think that precludes using data > from ACPI. We could just prevent the driver from loading if the machine > isn't whitelisted in DMI matches, and still use ACPI data. I also think about DMI as a narrowing scope of supported platforms. -- With Best Regards, Andy Shevchenko
