[PATCH v2 0/3] ath79: flush every write buffer of a shared CPU interrupt

[Rosen Penev <rosenp@gmail.com>]

On AR934x and QCA953x, the WMAC and the PCIe root complex share CPU
interrupt 2, but each writes to DDR through its own write buffer in the
DDR controller. The ath79 CPU interrupt controller flushes one write
buffer per interrupt before running its handlers, so only the buffer
listed last in the device tree gets flushed, and the other device can
read stale descriptors.

Patch 1 documents in the binding that a CPU interrupt may be listed
once per write buffer. Patch 2 keeps a mask of write buffers per CPU
interrupt and flushes all of them, and documents how the interrupt
lines, the write buffers and the flush fit together. Patch 3, suggested
by Thomas, starts the flushes of all the buffers of an interrupt before
waiting for any of them, so they drain in parallel, and replaces the
"It must be run twice" comment with what the AR7100 datasheet says
about it.

Patch 3 changes the signature of ath79_ddr_wb_flush() and its call site
in the irqchip driver, so patches 2 and 3 should go through the same
tree.

Changes since v1:
- Add dt-binding change.
- Add a comment describing the interrupt wiring and the write buffers
  (Thomas)
- New patch 3: flush the write buffers of an interrupt in parallel, and
  document the double flush from the AR7100 datasheet (Thomas)

Build tested with ath79_defconfig (LLVM, W=1).

Claude Code (Claude Opus 5.5) helped write the comments, patch 3 and
the commit messages, and searched the Atheros datasheets for the
double-flush requirement. I reviewed all the changes.

Rosen Penev (3):
  dt-bindings: interrupt-controller: qca,ar7100-cpu-intc: allow shared
    write buffer interrupts
  irqchip/ath79-cpu: flush every write buffer of a shared interrupt
  MIPS: ath79: flush the DDR write buffers of an interrupt in parallel

 .../qca,ar7100-cpu-intc.yaml                  |  5 +-
 arch/mips/ath79/common.c                      | 51 ++++++++++++++-----
 arch/mips/include/asm/mach-ath79/ath79.h      |  2 +-
 drivers/irqchip/irq-ath79-cpu.c               | 44 ++++++++++------
 4 files changed, 73 insertions(+), 29 deletions(-)

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2.56.0