Phone calls and text messages are way different than push notifications. The modem is a separate chip on the device that can almost definitely wake up the CPU, and there is, to my knowledge, no such chip for fetching push notifications over the internet. Even if there was, you can verify by hand that apps like tdesktop don’t support any kind of central push notification service from the operating system, so it would be impossible for the device to do anything special; it simply has to be awake for traditional apps to process push notifications.
Libnotify is for sending notifications to the OS for display. However “push notifications” usually refers to the system that handles the push portion. For example, APNS (Apple Push Notification Service) and FCM (Firebase Cloud Messaging.) Lacking a centralized service both on the OS side and in the cloud, it’s difficult to see how a battery-optimized push notification system could be devised. From my understanding, on today’s phones generally the CPU has to wake up periodically to poll, and if you have many individual push services that would be inefficient. (Maybe iPhone has a more clever system than just waking up the main CPU to poll, I do not know.)
You can possibly use the modem itself for monitoring for notifications, even if the main SoC sleeps. And wake the main SoC up from the modem. It would only work over mobile data though.
Modem firmware is, but the Linux running on the modem isn't. It's under GPL. Some people would even like to run mainline Linux there, eventually.
Even the userspace running on the modem can hardly be called completely proprietary. It's some busybox system + bunch of other tools that are also under GPL or other OSS licenses. I didn't measure it exactly, but it wouldn't surprise me if the amount of proprietary code in userspace of the modem is < 20%.
Sure I can. Modem's firmware is split into two parts. Linux OS running on ARM CPU and modem's modem FW running on hexagon cores. It's possible to modify ARM CPU code without affecting modem's operation much at all. ARM CPU just takes care of some audio/USB and such interfacing tasks. It's laregely free to run your own tasks. The manufacturer even allows customers to build their own userspace code for the ARM CPU inside the modem and extend it this way as part of quectel open linux SDK.
Anyway, the original issue was about notifications, and ability to implement them without consuming too much power. And one of ways to do it is to extend the modem this way.
Even if this is true, you still need to coordinate all of them to happen at once, so it doesn't obviate the need for an OS-level service to coordinate this at least.
Libnotify is for sending notifications to the OS for display. However “push notifications” usually refers to the system that handles the push portion. For example, APNS (Apple Push Notification Service) and FCM (Firebase Cloud Messaging.) Lacking a centralized service both on the OS side and in the cloud, it’s difficult to see how a battery-optimized push notification system could be devised. From my understanding, on today’s phones generally the CPU has to wake up periodically to poll, and if you have many individual push services that would be inefficient. (Maybe iPhone has a more clever system than just waking up the main CPU to poll, I do not know.)