For controllers with battery sensing capability (AST2600/AST2700), the last
channel uses a different circuit design optimized for battery voltage
measurement. This channel should not be enabled by default along with other
channels to avoid potential interference and power efficiency issues.

Changes made:
- Introduce aspeed_adc_get_active_channels() to return the number of
  channels that should be enabled by default
- For battery sensing capable controllers, exclude the last channel
  from the default channel enable mask
- Enable the battery sensing channel only when explicitly accessed
  via read_raw()
- Replace hardcoded channel numbers with ASPEED_ADC_BATTERY_CHANNEL macro
- Add helper functions for cleaner channel management

This ensures optimal power efficiency for normal ADC operations while
maintaining full functionality when battery sensing is needed.

Signed-off-by: Billy Tsai <billy_tsai@aspeedtech.com>
---
Changes in v2:
- Split the changes into a series of patches for better clarity and
review
- Link to v1: https://lore.kernel.org/r/20260313-adc-v1-1-7a2edb4e5664@aspeedtech.com

---
Billy Tsai (3):
      iio: adc: Add battery channel definition for ADC
      iio: adc: Enable multiple consecutive channels based on model data
      iio: adc: aspeed: Reserve battery sensing channel for on-demand use

 drivers/iio/adc/aspeed_adc.c | 75 ++++++++++++++++++++++++++++++++++++++------
 1 file changed, 65 insertions(+), 10 deletions(-)
---
base-commit: 6de23f81a5e08be8fbf5e8d7e9febc72a5b5f27f
change-id: 20260313-adc-479b0ab09bae

Best regards,
-- 
Billy Tsai <billy_tsai@aspeedtech.com>