[PATCH v4 00/11] clk: sunxi-ng: Consider alternative parent rates when determining NKM clock rate

[Frank Oltmanns <frank@oltmanns.dev>]

This patchset enables NKM clocks to consider alternative parent rates
and utilize this new feature to adjust the pll-video0 clock on Allwinner
A64 (PATCH 2 and 3).

Furthermore, with this patchset pll-video0 considers rates that are
higher than the requested rate when finding the closest rate. In
consequence, higher rates are also considered by pll-video0's
descandents (PATCH 4 et. seq.). In total, after applying this patchset,
finding the closest rate is supported by:
  - ccu_nm
  - ccu_nkm
  - ccu_mux
  - ccu_div

This allows us to achieve an optimal rate for driving the board's panel.

To provide some context, the clock structure involved in this process is
as follows:
    clock                       clock type
    --------------------------------------
    pll-video0                  ccu_nm
       pll-mipi                 ccu_nkm
          tcon0                 ccu_mux
             tcon-data-clock    sun4i_dclk

The divider between tcon0 and tcon-data-clock is fixed at 4. Therefore,
in order to achieve a rate that closely matches the desired rate of the
panel, pll-mipi needs to operate at a specific rate.

Tests
=====
So far, this has been successfully tested on the A64-based Pinephone
using three different panel rates:

 1. A panel rate that can be matched exactly by pll-video0.
 2. A panel rate that requires pll-video0 to undershoot to get the
    closest rate.
 3. A panel rate that requires pll-video0 to overshoot to get the
    closest rate.

Test records:

Re 1:
-----
Panel requests tcon-data-clock of 103500000 Hz, i.e., pll-mipi needs to
run at 414000000 Hz. This results in the following clock rates:
   clock                            rate
   -------------------------------------
    pll-video0                 207000000
       hdmi-phy-clk             51750000
       hdmi                    207000000
       tcon1                   207000000
       pll-mipi                414000000
          tcon0                414000000
             tcon-data-clock   103500000

The results of the find_best calls:
ccu_nkm_find_best_with_parent_adj: rate=414000000, best_rate=414000000, best_parent_rate=207000000, n=1, k=2, m=1
ccu_nkm_find_best_with_parent_adj: rate=414000000, best_rate=414000000, best_parent_rate=207000000, n=1, k=2, m=1
ccu_nkm_find_best_with_parent_adj: rate=414000000, best_rate=414000000, best_parent_rate=207000000, n=1, k=2, m=1
ccu_nkm_find_best_with_parent_adj: rate=414000000, best_rate=414000000, best_parent_rate=207000000, n=1, k=2, m=1
ccu_nkm_find_best: rate=414000000, best_rate=414000000, parent_rate=207000000, n=1, k=2, m=1

Re 2:
-----
Panel requests tcon-data-clock of 103650000 Hz, i.e., pll-mipi needs to
run at 414600000 Hz. This results in the following clock rates:
   clock                            rate
   -------------------------------------
    pll-video0                 282666666
       hdmi-phy-clk             70666666
       hdmi                    282666666
       tcon1                   282666666
       pll-mipi                414577776
          tcon0                414577776
             tcon-data-clock   103644444

The results of the find_best calls:
ccu_nkm_find_best_with_parent_adj: rate=414600000, best_rate=414577776, best_parent_rate=282666666, n=11, k=2, m=15
ccu_nkm_find_best_with_parent_adj: rate=414600000, best_rate=414577776, best_parent_rate=282666666, n=11, k=2, m=15
ccu_nkm_find_best_with_parent_adj: rate=414577776, best_rate=414577776, best_parent_rate=282666666, n=11, k=2, m=15
ccu_nkm_find_best_with_parent_adj: rate=414577776, best_rate=414577776, best_parent_rate=282666666, n=11, k=2, m=15
ccu_nkm_find_best: rate=414577776, best_rate=414577776, parent_rate=282666666, n=11, k=2, m=15

Here, we first ask pll-video0 for a rate that it can't provide exactly:
 - rate=414600000: We ask the parent for rate * m / (n * k) = 282681818,
   it returns 282666666. Here the parent undershoots.
Later we ask pll-video0 for exactly that rate again:
 - rate=414577776: We ask the parent for DIV_ROUND_UP(rate * m, n * k) =
   282666666, which it then returns.

Re 3:
-----
Panel requests tcon-data-clock of 112266000 Hz, i.e., pll-mipi needs to
run at 449064000 Hz. This results in the following clock rates:
   clock                            rate
   -------------------------------------
    pll-video0                 207272727
       hdmi-phy-clk             51818181
       hdmi                    207272727
       tcon1                   207272727
       pll-mipi                449090908
          tcon0                449090908
             tcon-data-clock   112272727

The results of the find_best calls:
ccu_nkm_find_best_with_parent_adj: rate=449064000, best_rate=449090908, best_parent_rate=207272727, n=13, k=2, m=12
ccu_nkm_find_best_with_parent_adj: rate=449064000, best_rate=449090908, best_parent_rate=207272727, n=13, k=2, m=12
ccu_nkm_find_best_with_parent_adj: rate=449090908, best_rate=449090908, best_parent_rate=207272727, n=13, k=2, m=12
ccu_nkm_find_best_with_parent_adj: rate=449090908, best_rate=449090908, best_parent_rate=207272727, n=13, k=2, m=12
ccu_nkm_find_best: rate=449090908, best_rate=449090908, parent_rate=207272727, n=13, k=2, m=12

Here, we first ask the pll-video0 for a rate that it can't provide
exactly:
 - rate=449064000: We ask the parent for DIV_ROUND_UP(rate * m, n * k) =
   207260308, it returns 207272727. Here the parent overshoots.
Later we ask pll-video0 for exactly that rate again:
 - rate=449090908: We ask the parent for DIV_ROUND_UP(rate * m, n * k) =
   207272727, which it then returns.

Changelog:
----------
Changes in v4:
 - Re-introduce a dedicated function for calculating the optimal parent
   rate for nkm clocks that was introduced in v2 and removed in v3. It
   turned out that not having this functionality introduces a bug when
   the parent does not support finding the closest rate:
   https://lore.kernel.org/all/87pm4xg2ub.fsf@oltmanns.dev/
 - Incorporate review remarks:
    - Correcting the parameter name for ccu_nkm_round_rate()'s parent HW
      is now in a separate patch.
    - Use correct parameter order in ccu_nkm_find_best_with_parent_adj.
    - Add ccu_is_better_rate() and use it for determining the best rate
      for nm and nkm, as well as ccu_mux_helper_determine_rate.
    - Consistently introduce new macros for clock variants that support
      finding the closest rate instead of updating existing macros.
    - Use wrapper function for determining a ccu_mux's rate in order to
      support finding the closest rate.
 - Link to v3: https://lore.kernel.org/r/20230702-pll-mipi_set_rate_parent-v3-0-46dcb8aa9cbc@oltmanns.dev

Changes in v3:
 - Use dedicated function for finding the best rate in cases where an
   nkm clock supports setting its parent's rate, streamlining it with
   the structure that is used in other sunxi-ng ccus such as ccu_mp
   (PATCH 1).
 - Therefore, remove the now obsolete comments that were introduced in
   v2 (PATCH 1).
 - Remove the dedicated function for calculating the optimal parent rate
   for nkm clocks that was introduced in v2. Instead use a simple
   calculation and require the parent clock to select the closest rate to
   achieve optimal results (PATCH 1).
 - Therefore, add support to set the closest rate for nm clocks (because
   pll-mipi's parent pll-video0 is an nm clock) and all clock types that
   are descendants of a64's pll-video0, i.e., nkm, mux, and div (PATCH 3
   et. seq.).
 - Link to v2: https://lore.kernel.org/all/20230611090143.132257-1-frank@oltmanns.dev/

Changes in V2:
 - Move optimal parent rate calculation to dedicated function
 - Choose a parent rate that does not to overshoot requested rate
 - Add comments to ccu_nkm_find_best
 - Make sure that best_parent_rate stays at original parent rate in the unlikely
   case that all combinations overshoot.

Link to V1:
https://lore.kernel.org/lkml/20230605190745.366882-1-frank@oltmanns.dev/

---
Frank Oltmanns (11):
      clk: sunxi-ng: nkm: Use correct parameter name for parent HW
      clk: sunxi-ng: nkm: consider alternative parent rates when determining rate
      clk: sunxi-ng: nkm: Improve determine rate when setting parent
      clk: sunxi-ng: a64: allow pll-mipi to set parent's rate
      clk: sunxi-ng: Add feature to find closest rate
      clk: sunxi-ng: Add helper function to find closest rate
      clk: sunxi-ng: nm: Support finding closest rate
      clk: sunxi-ng: nkm: Support finding closest rate
      clk: sunxi-ng: mux: Support finding closest rate
      clk: sunxi-ng: div: Support finding closest rate
      clk: sunxi-ng: a64: select closest rate for pll-video0

 drivers/clk/sunxi-ng/ccu-sun50i-a64.c | 36 ++++++++---------
 drivers/clk/sunxi-ng/ccu_common.c     | 12 ++++++
 drivers/clk/sunxi-ng/ccu_common.h     |  6 +++
 drivers/clk/sunxi-ng/ccu_div.h        | 30 ++++++++++++++
 drivers/clk/sunxi-ng/ccu_mux.c        | 15 ++++++-
 drivers/clk/sunxi-ng/ccu_mux.h        | 38 +++++++++++++-----
 drivers/clk/sunxi-ng/ccu_nkm.c        | 76 +++++++++++++++++++++++++++++++----
 drivers/clk/sunxi-ng/ccu_nm.c         | 11 ++---
 drivers/clk/sunxi-ng/ccu_nm.h         | 48 ++++++++++++++++++++--
 9 files changed, 222 insertions(+), 50 deletions(-)
---
base-commit: 6995e2de6891c724bfeb2db33d7b87775f913ad1
change-id: 20230626-pll-mipi_set_rate_parent-3363fc0d6e6f

Best regards,
-- 
Frank Oltmanns <frank@oltmanns.dev>