[PATCH v2 0/3] clk: sunxi-ng: fix the A523/T527 GPU clock model, enable GPU DVFS

Hi,

v2 of the A523/T527 GPU clock series.  v1 is here:
https://lore.kernel.org/linux-sunxi/[email protected]/

The GPU mod clock is not a linear M+1 divider: the M factor masks M pulses
out of every 16 parent cycles, so rate = parent * (16 - M) / 16 (T527 user
manual v0.92, section 2.7.6.58).  Modelling it with ccu_div programs a faster
clock than requested for every M > 0, which is what mainline does today.

Measured on an Orange Pi 4A with the Mali cycle counter, the OPPs labelled
150/200/300/400 MHz were really running at 487/648/560/750 MHz, and thermal
throttling to "400" actually raised the clock to 750.  With this series the
same measurement gives 149/199/300/399/597 MHz.

Changes since v1:

 - Dropped the pll-gpu reparenting notifier (patch 3/4 in v1).  I wrote it
   when the plan for the higher speed-bin points was to retune pll-gpu at
   runtime: it parked the GPU on the fixed pll-periph0-600M output while the
   PLL was being reprogrammed, so the GPU would never see it relocking.  That
   plan has been superseded.  The maskdiv in patch 1 can divide any parent
   down, and the speed-bin work on top of it (first follow-up below) pins
   pll-gpu once via assigned-clock-rates and reaches every operating point by
   moving only the mux and the divider.  The PLL therefore never changes rate
   at runtime, the notifier can never fire, and gpu_clk deliberately does not
   set CLK_SET_RATE_PARENT either.  That is how the 696 MHz point runs here
   today, with no notifier.  It would only be needed again if a future series
   reprograms the PLL instead of pinning it.  Chen-Yu, you asked for this
   notifier in the v1 discussion: tell me if you would rather have it now
   anyway and I will put it back.

 - maskdiv: honour CCU_FEATURE_UPDATE_BIT and CCU_FEATURE_KEY_FIELD in
   set_rate, clamp determine_rate() to the request bounds, and document that
   CLK_SET_RATE_PARENT is not supported.  These were folded into patch 1 so
   the new type is correct as introduced, rather than introduced and then
   fixed.  They also address the two issues the CI bot reported on v1.

 - The GPU OPP table moved from the board .dts to sun55i-a523.dtsi, and the
   operating-points-v2 reference now lives in the SoC's GPU node (Chen-Yu).

 - opp-microvolt now uses the <target min max> form, <900000 900000 920000>:
   900 mV is what the BSP universal table specifies, and the 920 mV ceiling
   covers boards whose GPU rail is a fixed 920 mV supply (Chen-Yu).

 - Rebased from v7.2-rc4 onto sunxi/for-next.

Tested on an Orange Pi 4A (T527, 2 GB): rates verified with the Mali cycle
counter under load, thermal-emulation throttling exercised, no job faults.

Two follow-ups are already working on the board and I can send them next.
Tell me which one is more useful to you first, or if you would rather they
waited:

 - GPU operating points above 600 MHz, gated on the SoC speed bin read from
   the SID.  This chip is bin 1, where the vendor table sanctions 696 MHz at
   the same 900 mV; it has been running games here without job faults.

 - The A523/T527 CPU clock unit (ccu-sun55i-a523-cpu.c) and the generic
   sunxi-ng fix it depends on, which is what cpufreq needs on this SoC.  The
   DSU/L3 clock lives in the same unit.

Juan Manuel López Carrillo (3):
  clk: sunxi-ng: add cycle-masking divider (maskdiv) clock type
  clk: sunxi-ng: sun55i-a523: GPU clock divider is fractional, not
    linear
  arm64: dts: allwinner: a523: add GPU OPP table

 .../arm64/boot/dts/allwinner/sun55i-a523.dtsi |  30 +++
 drivers/clk/sunxi-ng/Makefile                 |   1 +
 drivers/clk/sunxi-ng/ccu-sun55i-a523.c        |  32 ++-
 drivers/clk/sunxi-ng/ccu_common.h             |   3 +
 drivers/clk/sunxi-ng/ccu_maskdiv.c            | 213 ++++++++++++++++++
 drivers/clk/sunxi-ng/ccu_maskdiv.h            |  76 +++++++
 drivers/clk/sunxi-ng/ccu_mux.c                |   2 -
 7 files changed, 349 insertions(+), 8 deletions(-)
 create mode 100644 drivers/clk/sunxi-ng/ccu_maskdiv.c
 create mode 100644 drivers/clk/sunxi-ng/ccu_maskdiv.h


base-commit: 859c0e1925332d413ca8f9159c8ca5d04eea32a2
-- 
2.47.3