Chris: I might be missing something here, but given that os_dev already has a reference count and that handles multiple folks opening/closing the device, does the underlying adc driver need a reference count itself? If it just returned no error if opened again this would be fine.
I do note that os_dev_open() and os_dev_close() always call the open/close handlers regardless of reference count. I wonder if that should be changed (meaning only call open/close once)? > On Jun 6, 2018, at 10:13 AM, Christopher Collins <ch...@runtime.io> wrote: > > On Wed, Jun 06, 2018 at 08:50:34AM -0700, will sanfilippo wrote: >> Hello: >> >> I am not the most familiar with the ADC device so it is possible that it was >> being used incorrectly but in any event I ran across something I wanted to >> discuss. The call to os_dev_open() allows a device to be opened multiple >> times (there is a reference count there). However, the call to >> nrf52_adc_open() returns an error (OS_EBUSY) if the device has already been >> opened. >> >> This presented a problem in the following case: consider two independent >> packages both of which want to use ADC_0. Each package is going to attempt >> to open the ADC device (since it has no idea if it was already opened) but >> the second attempt to open the device will result in an error code returned. >> Depending on how the code is written in the package, this could be a >> problem. Given that an ADC is almost always a mutli-channel peripheral (one >> adc device has multple channels) I would suspect the above case to be >> common: multiple packages wanting an ADC channel from a single device. >> >> I am not sure if anything needs to be done here; just wanted to see if folks >> thought there should different behavior with regards to the function >> returning an error if the device was already opened. If not, folks are going >> to have to be careful when they write code using the adc device. Seems to me >> if nothing is going to change we have two options: >> >> 1) The device gets created and opened in some place and handed to the >> packages that need it. >> 2) The device gets created (say by the bsp) and each package can attempt to >> open the device. If os_dev_lookup() returns !NULL but os_dev_open() returns >> NULL it means that the device has already been opened. >> >> Something about #2 just sort of bothers me. I do not like ambiguous stuff >> like that; how do you know if there was an error for another reason? > > Why not: > > 3) Make the ADC driver consistent with other drivers by adding a > reference count. > > ? > > I know something less than nothing about the ADC code, so I could > certainly be missing something. > > Chris
