On Wed, 2022-03-09 at 11:11 +0200, Tony Lindgren wrote: > Hi, > > * Matthias Schiffer <matthias.schiffer@xxxxxxxxxxxxxxx> [220228 > 10:29]: > > AFAICT, disabling non-operatational devices in the board DTS > > instead of > > the SoC DTSI is worse than the alternatives in every way: > > > > - Verbose board DTS: You have to think about all the devices that > > exist > > in the SoC, not just the ones you want to use > > - Adding new nodes without `status = "disabled" to SoC DTSI can > > potentially cause issues on dependent boards > > - It doesn't solve the issues that not having `status = "disabled"` > > in > > the DTSI is supposed to solve > > My preference is the least amount of tinkering in the dts files > naturally :) It really does not matter if the extra dts churn is to > enable or disable devices, it should not be needed at all. > > To summarize, my main point really is the following: > > There should not be any need to tag the SoC internal devices with > anything > in the dts files. The device drivers should be able to just deal with > the > situation. IMO devices should be tagged with disabled or reserved > when > they are not accessible for example because of being used by secure > mode > for example. If the the status needs to be set to anything, it really > is > a symptom of incomplete handling somewhere. > > Regards, > > Tony Hi Tony, while I agree that it would be great if drivers could just detect when hardware is not available, this is simply not how most drivers work - when you instantiate the driver via a non-disabled(/reserved/...) DT node, the driver expects a usable device. Especially for busses like I2C, there is no way for a driver to reliably detect whether the bus is usable or not. (There are several states that can't really be distinguished: Is pinmuxing missing, or does the device not need any muxing? Is a line low because it is not actually connected to anything, or is there another master currently using the bus, or is the bus stuck due to a faulty device?) Which is why it is the convention for SoC DTSI files disable nodes for devices that may be unusable. Taking UARTs as an example, a quick grep for "serial@" nodes in arch/arm/boot/dts/*.dtsi and arch/arm64/boot/dts/*/*.dtsi shows that the vast majority of these nodes is disabled by default. Regards, Matthias
