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

[Niklas Cassel <cassel@kernel.org>]

Hello Koichiro,

On Thu, Feb 19, 2026 at 01:19:02AM +0900, Koichiro Den wrote:
> On Mon, Feb 16, 2026 at 12:22:14AM +0900, Koichiro Den wrote:
> > 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@valinux.co.jp/
> > 
> > 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(-)
> 
> +CC: Niklas
> 
> Niklas provided valuable feedback in the previous iterations and also helped
> test the earlier (non-split) series mentioned above. During testing, he
> identified that on platforms where chip->nr_irqs > 1, the interrupt emulation
> IRQ could be randomly delivered to one of the shared channel IRQs [1]. That
> observation was the main motivation for the rework.
> 
> I missed Niklas in CC earlier, sorry about that. I had naively relied on
> get_maintainers.pl. I'll be more careful.

Thank you for CC:ing me.

I'm happy to help with testing.

For reviewing, I will limit myself to drivers/pci/endpoint.
(I don't really have spare cycles to also review drivers/dma/dw-edma patches.)


Kind regards,
Niklas