[PATCH 0/2] dmaengine: dw-edma: Interrupt-emulation doorbell support

[Koichiro Den]

Hi,

Some DesignWare eDMA instances support "interrupt emulation", where a
software write can assert the IRQ line without setting the normal
DONE/ABORT status bits.

In the current mainline, on implementations that support interrupt
emulation, writing once to DMA_{WRITE,READ}_INT_STATUS_OFF is sufficient
to leave the level-triggered IRQ line asserted. Since the shared dw-edma
IRQ handlers only look at DONE/ABORT bits and do not perform any
deassertion sequence for interrupt emulation, the IRQ remains asserted
and is eventually disabled by the generic IRQ layer:

  $ sudo devmem2 0xe65d50a0 w 0

  [   47.189557] irq 48: nobody cared (try booting with the "irqpoll" option)
  ...
  [   47.190383] handlers:
  [   47.199837] [<00000000a5ecb36e>] dw_edma_interrupt_common
  [   47.200214] Disabling IRQ #48

In other words, a single interrupt-emulation write can leave the IRQ
line stuck asserted and render the DMA engine unusable until reboot.

This series fixes the problem by:

  - adding a core hook to deassert an emulated interrupt
  - wiring a requestable Linux virtual IRQ whose .irq_ack performs the
    deassert sequence
  - raising that virtual IRQ from the dw-edma IRQ path to ensure the
    deassert sequence is always executed

This makes interrupt emulation safe and also enables platform users to
expose it as a doorbell via the exported db_irq and db_offset.

This is a spin-off from:
https://lore.kernel.org/linux-pci/20260209125316.2132589-1-den@xxxxxxxxxxxxx/

Based on dmaengine.git next branch latest:
Commit ab736ed52e34 ("dmaengine: add Frank Li as reviewer")

Thanks for reviewing,


Koichiro Den (2):
  dmaengine: dw-edma: Add interrupt-emulation hooks
  dmaengine: dw-edma: Add virtual IRQ for interrupt-emulation doorbells

 drivers/dma/dw-edma/dw-edma-core.c    | 127 +++++++++++++++++++++++++-
 drivers/dma/dw-edma/dw-edma-core.h    |  17 ++++
 drivers/dma/dw-edma/dw-edma-v0-core.c |  21 +++++
 drivers/dma/dw-edma/dw-hdma-v0-core.c |   7 ++
 include/linux/dma/edma.h              |   6 ++
 5 files changed, 173 insertions(+), 5 deletions(-)

-- 
2.51.0