On Wed, Sep 26, 2018 at 10:26 PM Rajat Jain <rajatja@xxxxxxxxxx> wrote: > On Wed, Sep 26, 2018 at 1:42 AM Andy Shevchenko > <andy.shevchenko@xxxxxxxxx> wrote: > > On Wed, Sep 26, 2018 at 10:49 AM Mika Westerberg > > <mika.westerberg@xxxxxxxxxxxxxxx> wrote: > > > Or you can use con_id=<actual string> everywhere and supply > > > acpi_dev_add_driver_gpios() where needed to cover cases where BIOS does > > > not provide _DSD. > > This sounds like a good idea and I'd like to do this. I have some > questions though: > > 1) If the BIOS does provide a _DSD entry for "cd-gpio", and > additionally driver also uses devm_acpi_dev_add_driver_gpios() to add > one more entry for the same string "cd-gpio", which one will (should?) > actually be returned by the gpiolib? The one in BIOS or the one that > was added by the driver? Of course the one that BIOS provides. This hardcoded mapping tables is a fallback for *old* BIOSes which do not have _DSD. > 2) Related, I'm trying to understand how can a driver use > devm_acpi_dev_add_driver_gpios(), for *only* the case where the BIOS > does not have a _DSD (Or should it really care)? Does the driver need > to check for _DSD using some other ACPI call? The magic happens internally in ACPI core. Whenever one calls gpiod_get() with a name on ACPI-enabled platform, _DSD would be checked first. > > See also Documentation/acpi/gpio-properties.txt for > > > more information. > > > In case of SDHCI I think the correct way is to stick using _CRS lookup > > > only because there typically is just one GpioInt() and I have not seen a > > > single BIOS yet where they implement _DSD for this besides yours. If > > > there is not way to change the BIOS implementation then I guess we just > > > need to amend the driver to call acpi_dev_add_driver_gpios(). > > Since we shouldn't discourage a BIOS that is trying to do the right > thing by exposing the details in _DST, I think it would be preferable > if we can solve this in the kernel. Patches are welcome, I think. Btw, is there any existing hardware on the market with such BIOS? -- With Best Regards, Andy Shevchenko
