linux-kernel - Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe path

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Message-ID: <20250305182858.GK5011@ziepe.ca>
Date: Wed, 5 Mar 2025 14:28:58 -0400
From: Jason Gunthorpe <jgg@...pe.ca>
To: Robin Murphy <robin.murphy@....com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>, Russell King <linux@...linux.org.uk>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Danilo Krummrich <dakr@...nel.org>,
	Stuart Yoder <stuyoder@...il.com>,
	Laurentiu Tudor <laurentiu.tudor@....com>,
	Nipun Gupta <nipun.gupta@....com>,
	Nikhil Agarwal <nikhil.agarwal@....com>,
	Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
	Rob Herring <robh@...nel.org>,
	Saravana Kannan <saravanak@...gle.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>, linux-acpi@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, devicetree@...r.kernel.org,
	linux-pci@...r.kernel.org,
	Charan Teja Kalla <quic_charante@...cinc.com>
Subject: Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe
 path

On Fri, Feb 28, 2025 at 03:46:33PM +0000, Robin Murphy wrote:
> +	if (!dev->driver && dev->bus->dma_configure) {
> +		mutex_unlock(&iommu_probe_device_lock);
> +		dev->bus->dma_configure(dev);
> +		mutex_lock(&iommu_probe_device_lock);
> +	}

I think it would be very nice to get rid of the lock/unlock.. It makes
me nervous that we continue on assuming dev->iommu was freshly
allocated..

 setup the dev->iommu partially, then drop the lock.

There is only one other caller in:

static int really_probe(struct device *dev, const struct device_driver *drv)
{
	if (dev->bus->dma_configure) {
		ret = dev->bus->dma_configure(dev);
		if (ret)
			goto pinctrl_bind_failed;
	}

Is it feasible to make it so the caller has to hold the
iommu_probe_device_lock prior to calling the op?

That would require moving the locking inside of_dma_configure to less
inside, and using a new iommu_probe_device() wrapper.

However, if you plan to turn this inside out soonish then it would not
be worth the bother.

Anyhow:

Reviewed-by: Jason Gunthorpe <jgg@...dia.com>

Jason