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

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Message-ID: <25bd5477-a388-405f-a976-6b1a59860ef8@arm.com>
Date: Tue, 18 Mar 2025 17:24:51 +0000
From: Robin Murphy <robin.murphy@....com>
To: Geert Uytterhoeven <geert@...ux-m68k.org>
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>,
 Linux-Renesas <linux-renesas-soc@...r.kernel.org>
Subject: Re: [PATCH v2 4/4] iommu: Get DT/ACPI parsing into the proper probe
 path

Hi Geert,

On 18/03/2025 4:37 pm, Geert Uytterhoeven wrote:
[...]
> Thanks for your patch, which is now commit bcb81ac6ae3c2ef9 ("iommu:
> Get DT/ACPI parsing into the proper probe path") in iommu/next.
> 
> This patch triggers two issues on R-Car Gen3 platforms:
> 
> 1. I am seeing a warning on Renesas Salvator-XS with R-Car M3N
> (but not on the similar board with R-Car H3), and only for SATA[1].
> Unfortunately commit 73d2f10957f517e5 ("iommu: Don't warn prematurely
> about dodgy probes") does not help:
[...]
>      Call trace:
>       __iommu_probe_device+0x208/0x38c (P)
>       iommu_probe_device+0x34/0x74
>       of_iommu_configure+0x128/0x200
>       of_dma_configure_id+0xdc/0x1d4
>       platform_dma_configure+0x48/0x6c
>       really_probe+0xf0/0x260
>       __driver_probe_device+0xec/0x104
>       driver_probe_device+0x3c/0xc0

Hurrah, this is the warning doing the correct job - something *is* off
if we're now getting here without the IOMMU configuration being done
already (for a normal device with no other funny business going on).

> 2. The IOMMU driver's iommu_ops.of_xlate() callback is called about
> three times as much as before:

That would suggest that the fwspec gets set up OK, then something later
in the __iommu_probe_device() path fails and tears it down again, so the
next attempt starts from scratch. Do you see the "Cannot attach to
IPMMU" message firing? And similarly to the Rockchip case, does the
below help?

Thanks,
Robin.

----->8-----
diff --git a/drivers/iommu/ipmmu-vmsa.c b/drivers/iommu/ipmmu-vmsa.c
index 074daf1aac4e..5d416262ae5f 100644
--- a/drivers/iommu/ipmmu-vmsa.c
+++ b/drivers/iommu/ipmmu-vmsa.c
@@ -1081,6 +1081,7 @@ static int ipmmu_probe(struct platform_device *pdev)
  		}
  	}

+	platform_set_drvdata(pdev, mmu);
  	/*
  	 * Register the IPMMU to the IOMMU subsystem in the following cases:
  	 * - R-Car Gen2 IPMMU (all devices registered)
@@ -1103,7 +1104,6 @@ static int ipmmu_probe(struct platform_device *pdev)
  	 * ipmmu_init() after the probe function returns.
  	 */

-	platform_set_drvdata(pdev, mmu);

  	return 0;
  }