On Mon, 10 Jun 2019, Ard Biesheuvel wrote: > On Mon, 10 Jun 2019 at 10:55, Lee Jones <lee.jones@xxxxxxxxxx> wrote: > > > > On Mon, 10 Jun 2019, Ard Biesheuvel wrote: > > > > > On Mon, 10 Jun 2019 at 10:42, Lee Jones <lee.jones@xxxxxxxxxx> wrote: > > > > > > > > This patch provides basic support for booting with ACPI instead > > > > of the currently supported Device Tree. When doing so there are a > > > > couple of differences which we need to taken into consideration. > > > > > > > > Firstly, the SDM850 ACPI tables omit information pertaining to the > > > > 4 reserved GPIOs on the platform. If Linux attempts to touch/ > > > > initialise any of these lines, the firmware will restart the > > > > platform. > > > > > > > > Secondly, when booting with ACPI, it is expected that the firmware > > > > will set-up things like; Regulators, Clocks, Pin Functions, etc in > > > > their ideal configuration. Thus, the possible Pin Functions > > > > available to this platform are not advertised when providing the > > > > higher GPIOD/Pinctrl APIs with pin information. > > > > > > > > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx> > > > > > > For the ACPI probing boilerplate: > > > Acked-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx> > > > > > > *However*, I really don't like hardcoding reserved GPIOs like this. > > > What guarantee do we have that each and every ACPI system > > > incorporating the QCOM0217 device has the exact same list of reserved > > > GPIOs? > > > > This is SDM845 specific, so the chances are reduced. > > You don't know that. All the evidence I have to hand tells me that this is the case. Even on very closely related variants Qualcomm uses different H/W blocks for GPIO. > > However, if another SDM845 variant does crop up, also lacking the > > "gpios" property, we will have to find another differentiating factor > > between them and conduct some matching. What else can you do with > > platforms supporting non-complete/non-forthcoming ACPI tables? > > > > Either we don't touch any pins at all if they are not referenced > explicitly anywhere I guess this would require an API change, which is out of scope of this patch-set. Happy to change this implementation later if the subsystem allows for it though. > or we parse the PEP tables, which seem to cover > some of this information (if Bjorn's analysis is correct) Maybe someone can conduct some further work on this when we start to enable or write a driver for the PEP (Windows-compatible System Power Management Controller). The tables for the PEP look pretty complex, so this task would be extremely difficult if not impossible without Qualcomm's help. I wouldn't even know how to extrapolate this information from the tables. > (if Bjorn's analysis is correct) Bjorn is about to provide his Reviewed-by for this implementation. -- Lee Jones [李琼斯] Linaro Services Technical Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog
