Re: [PATCH v3 15/18] dmaengine: ste_dma40: Use power domain for LCLA SRAM

[Vinod Koul <vkoul@kernel.org>]

On 24-09-26, 15:26, Ulf Hansson wrote:
> On Mon, Sep 21, 2026 at 12:49 AM Linus Walleij <linusw@kernel.org> wrote:
> >
> > Replace the LCLA ESRAM regulator with runtime PM.
> >
> > Use the SRAM device that owns the ESRAM34 power domain.
> >
> > Hold that domain while DMA transfers are active. The DMA controller is
> > runtime PM IRQ-safe, so keep taking explicit LCLA runtime PM references
> > from the descriptor preparation path instead of relying on a runtime PM
> > device link from the atomic transfer path.
> 
> A bit of an orthogonal problem, but related to the above. The irqsafe
> thing have been discussed in the past for DMA controller drivers.
> 
> Would it possible to get rid of the irqsafe configuration for the dma
> controller device, altogether?
> 
> I don't recall exactly, but not the entire consumer DMA API is allowed
> to be called in atomic context, but perhaps that is not sufficient to
> allow us to drop the irqsafe configuration for the DMA controller
> device?
> 
> If not, I wonder if the consumer of the DMA (like an mmc controller)
> should be assigned as a consumer device (using device links and
> DL_FLAG_PM_RUNTIME) of the DMA controller device. In this way, the
> consumer (mmc) would be able to control the supplier (DMA) through the
> device link directly using runtime PM. This could potentially avoid
> the requirement of having to use irqsafe for the DMA controller
> device. Maybe someone already tried this?
> 
> If the irqsafe configuration can be dropped, in some way or the other,
> this patch could become less intrusive, as all that would be needed is
> to create a device link to sram device using DL_FLAG_PM_RUNTIME.

That is a consequence of dmaengine work running in tasklet and thus
softirq mode. The dmaengine tasks need to run with a higher priority to
enable higher dmaengine throughput. We have plans to move to WQ_BH [1], but
I think that runs in softirq mode as well...

[1]: cover.1786384168.git.allen.lkml@gmail.com
-- 
~Vinod