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Message-ID: <aYTAUFT3LstnaHey@lizhi-Precision-Tower-5810>
Date: Thu, 5 Feb 2026 11:07:44 -0500
From: Frank Li <Frank.li@....com>
To: Koichiro Den <den@...inux.co.jp>
Cc: vkoul@...nel.org, mani@...nel.org, jingoohan1@...il.com,
lpieralisi@...nel.org, kwilczynski@...nel.org, robh@...nel.org,
bhelgaas@...gle.com, dmaengine@...r.kernel.org,
linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 04/11] dmaengine: Add selfirq callback registration API
On Thu, Feb 05, 2026 at 03:50:59PM +0900, Koichiro Den wrote:
> On Wed, Feb 04, 2026 at 12:46:36PM -0500, Frank Li wrote:
> > On Wed, Feb 04, 2026 at 11:54:32PM +0900, Koichiro Den wrote:
> > > Some DMA controllers can generate an interrupt by software writing to a
> > > register, without updating the normal interrupt status bits. This can be
> > > used as a doorbell mechanism when the DMA engine is remotely programmed,
> > > or for self-tests.
> > >
> > > Add an optional per-DMA-device API to register/unregister callbacks for
> > > such "selfirq" events. Providers may invoke these callbacks from their
> > > interrupt handler when they detect an emulated interrupt.
> > >
> > > Callbacks are invoked in hardirq context and must not sleep.
> >
> > Is it possible register shared irq handle with the same channel's irq
> > number?
>
> The proposed dmaengine_{register,unregister}_selfirq() APIs are device-wide
> (i.e. not per channel), so I'm not sure which "channel" you refer to here.
> Also, when chip->nr_irqs > 1 on EP, dw-edma distributes channels across
> multiple IRQ vectors, and it's unclear (at least to me) which IRQ vector
> the emulated interrupt ("fake irq") is expected to be delivered on.
>
> That said, technically, yes I agree adding another handler should be
> possible, as dw-edma currently requests its irq(s) with IRQF_SHARED.
> However, for a consumer driver to do request_irq() on its own, I think it
> would need a stable way to obtain the irq number. Today that mapping seems
> platform-specific and hidden behind dw_edma_plat_ops->irq_vector().
next patch, you add API to get resource, irq number should be one type of
resource.
Frank
>
> Would you prefer exposing a helper for obtaining the irq number (or
> exporting the mapping in some form) instead of adding the dmaengine selfirq
> API, or did you have another approach in mind?
>
> Thanks for the review,
> Koichiro
>
> >
> > Frank
> >
> > >
> > > Signed-off-by: Koichiro Den <den@...inux.co.jp>
> > > ---
> > > include/linux/dmaengine.h | 70 +++++++++++++++++++++++++++++++++++++++
> > > 1 file changed, 70 insertions(+)
> > >
> > > diff --git a/include/linux/dmaengine.h b/include/linux/dmaengine.h
> > > index 71bc2674567f..9c6194e8bfe1 100644
> > > --- a/include/linux/dmaengine.h
> > > +++ b/include/linux/dmaengine.h
> > > @@ -785,6 +785,17 @@ struct dma_filter {
> > > const struct dma_slave_map *map;
> > > };
> > >
> > > +/**
> > > + * dma_selfirq_fn - callback for emulated/self IRQ events
> > > + * @dev: DMA device invoking the callback
> > > + * @data: opaque pointer provided at registration time
> > > + *
> > > + * Providers may invoke this callback from their interrupt handler when an
> > > + * emulated interrupt ("selfirq") might have occurred. The callback runs in
> > > + * hardirq context and must not sleep.
> > > + */
> > > +typedef void (*dma_selfirq_fn)(struct dma_device *dev, void *data);
> > > +
> > > /**
> > > * struct dma_device - info on the entity supplying DMA services
> > > * @ref: reference is taken and put every time a channel is allocated or freed
> > > @@ -853,6 +864,10 @@ struct dma_filter {
> > > * or an error code
> > > * @device_synchronize: Synchronizes the termination of a transfers to the
> > > * current context.
> > > + * @device_register_selfirq: optional callback registration for
> > > + * emulated/self IRQ events
> > > + * @device_unregister_selfirq: unregister previously registered selfirq
> > > + * callback
> > > * @device_tx_status: poll for transaction completion, the optional
> > > * txstate parameter can be supplied with a pointer to get a
> > > * struct with auxiliary transfer status information, otherwise the call
> > > @@ -951,6 +966,11 @@ struct dma_device {
> > > int (*device_terminate_all)(struct dma_chan *chan);
> > > void (*device_synchronize)(struct dma_chan *chan);
> > >
> > > + int (*device_register_selfirq)(struct dma_device *dev,
> > > + dma_selfirq_fn fn, void *data);
> > > + void (*device_unregister_selfirq)(struct dma_device *dev,
> > > + dma_selfirq_fn fn, void *data);
> > > +
> > > enum dma_status (*device_tx_status)(struct dma_chan *chan,
> > > dma_cookie_t cookie,
> > > struct dma_tx_state *txstate);
> > > @@ -1197,6 +1217,56 @@ static inline void dmaengine_synchronize(struct dma_chan *chan)
> > > chan->device->device_synchronize(chan);
> > > }
> > >
> > > +/**
> > > + * dmaengine_register_selfirq() - Register a callback for emulated/self IRQ
> > > + * events
> > > + * @dev: DMA device
> > > + * @fn: callback invoked from the provider's IRQ handler
> > > + * @data: opaque callback data
> > > + *
> > > + * Some DMA controllers can raise an interrupt by software writing to a
> > > + * register without updating normal status bits. Providers may call
> > > + * registered callbacks from their interrupt handler when such events may
> > > + * have occurred.
> > > + * Callbacks are invoked in hardirq context and must not sleep.
> > > + *
> > > + * Return: 0 on success, -EOPNOTSUPP if unsupported, -EINVAL on bad args,
> > > + * or provider-specific -errno.
> > > + */
> > > +static inline int dmaengine_register_selfirq(struct dma_device *dev,
> > > + dma_selfirq_fn fn, void *data)
> > > +{
> > > + if (!dev || !fn)
> > > + return -EINVAL;
> > > + if (!dev->device_register_selfirq)
> > > + return -EOPNOTSUPP;
> > > +
> > > + return dev->device_register_selfirq(dev, fn, data);
> > > +}
> > > +
> > > +/**
> > > + * dmaengine_unregister_selfirq() - Unregister a previously registered
> > > + * selfirq callback
> > > + * @dev: DMA device
> > > + * @fn: callback pointer used at registration time
> > > + * @data: opaque pointer used at registration time
> > > + *
> > > + * Unregister a callback previously registered via
> > > + * dmaengine_register_selfirq(). Providers may synchronize against
> > > + * in-flight callbacks, therefore this function may sleep and must not be
> > > + * called from atomic context.
> > > + */
> > > +static inline void dmaengine_unregister_selfirq(struct dma_device *dev,
> > > + dma_selfirq_fn fn, void *data)
> > > +{
> > > + if (!dev || !fn)
> > > + return;
> > > + if (!dev->device_unregister_selfirq)
> > > + return;
> > > +
> > > + dev->device_unregister_selfirq(dev, fn, data);
> > > +}
> > > +
> > > /**
> > > * dmaengine_terminate_sync() - Terminate all active DMA transfers
> > > * @chan: The channel for which to terminate the transfers
> > > --
> > > 2.51.0
> > >
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