[PATCH v4 0/8] i.MX early debug UART clock fixes

[Lucas Stach]

This series fixes a long standing interaction issue between the
kernels early debug facilities and the i.MX clock drivers.

Both earlyprintk and earlycon rely on the bootloader setup clocks
for the UARTs to be retained during kernel init. As those clocks are
only enabled in hardware, but not referenced in software they (or even
their parent clocks) may get disabled as a result of other clocks being
en-/disabled during boot.

This results in missing messages from the early debug console until the
regular system console takes over, or even worse system hangs in response
to unclocked register accesses. This renders those debugging facilities a
lot less useful.

The fix implemented here is to check if any of this early debugging is
enabled and keep the UART clocks referenced and enabled in that case.
The clocks will then only be disabled at the end of kernel init, at which
point the real console should have taken over and the early outputs being
disabled.

I've runtime tested this on i.MX6Q and i.MX53, other platforms are only
compile tested. This is mostly a mechanical change, but still I would
appreciate some testing.

Changes since v1:
- reworked logic to require significantly less code in the individual
  clock drivers

Changes since v2:
- fix checkpatch warning about initdata annotation placement
- make code a bit more compact in the for(...) loops
  (since 2 people already commented about this I made up my mind)
- change code style in driver as requested by Shawn
- add more const correctness
  (note that this triggers a false positive checkpatch error in the first patch)

Changes since v3:
- make sure to only execute late_initcall code if init functions have been called
  (fixes OOPS on others SoCs in multiplatform config)

Regards,
Lucas

Lucas Stach (8):
  clk: imx: add common logic to detect early UART usage
  clk: imx25: retain early UART clocks during kernel init
  clk: imx27: retain early UART clocks during kernel init
  clk: imx31: retain early UART clocks during kernel init
  clk: imx35: retain early UART clocks during kernel init
  clk: imx5: retain early UART clocks during kernel init
  clk: imx6: retain early UART clocks during kernel init
  clk: imx7d: retain early UART clocks during kernel init

 drivers/clk/imx/clk-imx25.c       | 12 ++++++++++++
 drivers/clk/imx/clk-imx27.c       | 13 +++++++++++++
 drivers/clk/imx/clk-imx31.c       | 12 ++++++++++++
 drivers/clk/imx/clk-imx35.c       | 10 ++++++++++
 drivers/clk/imx/clk-imx51-imx53.c | 16 ++++++++++++++++
 drivers/clk/imx/clk-imx6q.c       |  8 ++++++++
 drivers/clk/imx/clk-imx6sl.c      |  8 ++++++++
 drivers/clk/imx/clk-imx6sx.c      |  8 ++++++++
 drivers/clk/imx/clk-imx7d.c       | 13 +++++++++++++
 drivers/clk/imx/clk.c             | 38 ++++++++++++++++++++++++++++++++++++++
 drivers/clk/imx/clk.h             |  1 +
 11 files changed, 139 insertions(+)

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2.5.1