Subject: Re: [PATCH rc v4 5/5] iommu/arm-smmu-v3: Detect ARM_SMMU_OPT_KDUMP_ADOPT in probe()

From: Nicolin Chen <[email-masked]>
Date: Sat, 9 May 2026 00:53:18 -0700

On Fri, May 08, 2026 at 07:47:22AM +0000, Tian, Kevin wrote:
> > From: Nicolin Chen <[email-masked]>
> > +	/*
> > +	 * If SMMU is already active in kdump case, there could be in-flight
> > DMA
> > +	 * from devices initiated by the crashed kernel.
> > +	 */
> > +	if (!(readl_relaxed(smmu->base + ARM_SMMU_CR0) &
> > CR0_SMMUEN))
> > +		return;
> 
> Above comment is for the entire function. for the check here the comment
> should be that no in-fly DMA to require adoption due to SMMU disabled.

Changed it to:
	/* No adoption if SMMU is disabled (i.e., there is no in-flight DMA) */

> > +
> > +	/* For now, only support a coherent SMMU that works with
> > MEMREMAP_WB */
> > +	if (!(smmu->features & ARM_SMMU_FEAT_COHERENCY)) {
> > +		dev_warn(smmu->dev,
> > +			 "kdump: non-coherent SMMU can't adopt stream
> > table\n");
> 
> "can't adopt stream table so SMMU will be reset to block all DMAs"

That'd be a bit too long. So, I changed it to:
	"kdump: non-coherent SMMU unsupported; reset to block all DMAs\n");

Thanks
Nicolin