Clock tree rework tracking issue

[bugadani]

This issue tracks the state of the clock tree rework.

• Proof of concept: Clock tree rework: ESP32 #4501
• Model clock trees of other chips
  • Redo ESP32-C2 clocktree, remove ESP_HAL_CONFIG_XTAL_FREQUENCY #4517
  • Describe ESP32-C3 clock tree in metadata #4527
  • ESP32-C5
  • Rework C6 clock tree #4553
  • ESP32-C61
  • Rework H2 clocktree #4595
  • ESP32-P4
  • Rework S2 clocktree #4610
  • S3: rework clocktree #4633
• Model all peripheral clock sources
• Expose new clock config options unstably #4660
• Model missing options in clock trees:
  • ESP32:
    • XTAL32K external oscillator option
    • Configurable CK8M (RC_FAST_CLK)
    • LOW_POWER_CLK
  • ...
• Detect XTL frequency on demand to support clocking CPU from RC_FAST_CLK
• Optimize away unnecessary reference counts
  • Mark which clock nodes may be manually requested. Peripheral clocks should be, but out of system clocks probably only CPU.
  • Optimize away refcounts where clock node has a single user #4512
  • ...?
• Add a bitmap that tracks active clocks (this can be postponed for upcoming low power rework)
• Ensure code generator orders the initial configuration properly - Sort config calls in topological order #4536
• Resolve Clock speed sometimes incorrect #4440
• Decide whether caching the configuration is necessary or we can restore from hardware
• Decide whether we should cache active frequencies, or calculating them from the configurations is good enough
  • We should likely cache, but we need to implement this in a way that does not require a critical section to read current frequencies. Since we expect a clock to not be running when configured, maybe that is enough to remain consistent?
• Implement equation-based PLL configuration (for ESP32 APLL)
• Remove ESP_HAL_CONFIG_XTAL_FREQUENCY - Redo ESP32-C2 clocktree, remove ESP_HAL_CONFIG_XTAL_FREQUENCY #4517
• Retain clock tree state between CPU-only resets
• Make configuration of always_on clocks and their dependencies mandatory
• Generate code directly into esp-hal, auto-update the list of handwritten functions
• Allow hand-written doc comments on clock nodes. Some types/config options need more explanation.
• Auto-generate on_changed callbacks
• Refactor TIMG source clocks #4665
• Refactor (LP_)UART clock sources #4667
• Improve clock node request/release API - Clean up MCPWM clock sources #4647 (comment)
• Add the ability to iterate over a mux's variants - 1e1388d#diff-f4823be2299dcbe2eea9219ec3ce12b28541a53c0f91e7c80428813abed2b309R183-R185

[Frostie314159]

I suppose, we can't make the RF clocks part of this due to the lack of info about them.

[bugadani]

What we can read out of esp-idf is definitely in scope, and there's plenty there still.