linux-kernel - Re: [PATCH v15 12/12] of: Add plumbing for restricted DMA pool

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Date:   Fri, 2 Jul 2021 14:18:29 +0100
From:   Will Deacon <will@...nel.org>
To:     Robin Murphy <robin.murphy@....com>
Cc:     Guenter Roeck <linux@...ck-us.net>,
        Claire Chang <tientzu@...omium.org>,
        Rob Herring <robh+dt@...nel.org>, mpe@...erman.id.au,
        Joerg Roedel <joro@...tes.org>,
        Frank Rowand <frowand.list@...il.com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        boris.ostrovsky@...cle.com, jgross@...e.com,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        heikki.krogerus@...ux.intel.com, thomas.hellstrom@...ux.intel.com,
        peterz@...radead.org, dri-devel@...ts.freedesktop.org,
        chris@...is-wilson.co.uk, grant.likely@....com, paulus@...ba.org,
        mingo@...nel.org, jxgao@...gle.com, sstabellini@...nel.org,
        Saravana Kannan <saravanak@...gle.com>, xypron.glpk@....de,
        "Rafael J . Wysocki" <rafael.j.wysocki@...el.com>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        bskeggs@...hat.com, linux-pci@...r.kernel.org,
        xen-devel@...ts.xenproject.org,
        Thierry Reding <treding@...dia.com>,
        intel-gfx@...ts.freedesktop.org, matthew.auld@...el.com,
        linux-devicetree <devicetree@...r.kernel.org>, airlied@...ux.ie,
        Nicolas Boichat <drinkcat@...omium.org>,
        rodrigo.vivi@...el.com, bhelgaas@...gle.com,
        Dan Williams <dan.j.williams@...el.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Greg KH <gregkh@...uxfoundation.org>,
        Randy Dunlap <rdunlap@...radead.org>, quic_qiancai@...cinc.com,
        lkml <linux-kernel@...r.kernel.org>, tfiga@...omium.org,
        "list@....net:IOMMU DRIVERS" <iommu@...ts.linux-foundation.org>,
        Jim Quinlan <james.quinlan@...adcom.com>,
        thomas.lendacky@....com, linuxppc-dev@...ts.ozlabs.org,
        bauerman@...ux.ibm.com
Subject: Re: [PATCH v15 12/12] of: Add plumbing for restricted DMA pool

On Fri, Jul 02, 2021 at 12:39:41PM +0100, Robin Murphy wrote:
> On 2021-07-02 04:08, Guenter Roeck wrote:
> > On Thu, Jun 24, 2021 at 11:55:26PM +0800, Claire Chang wrote:
> > > If a device is not behind an IOMMU, we look up the device node and set
> > > up the restricted DMA when the restricted-dma-pool is presented.
> > > 
> > > Signed-off-by: Claire Chang <tientzu@...omium.org>
> > > Tested-by: Stefano Stabellini <sstabellini@...nel.org>
> > > Tested-by: Will Deacon <will@...nel.org>
> > 
> > With this patch in place, all sparc and sparc64 qemu emulations
> > fail to boot. Symptom is that the root file system is not found.
> > Reverting this patch fixes the problem. Bisect log is attached.
> 
> Ah, OF_ADDRESS depends on !SPARC, so of_dma_configure_id() is presumably
> returning an unexpected -ENODEV from the of_dma_set_restricted_buffer()
> stub. That should probably be returning 0 instead, since either way it's not
> an error condition for it to simply do nothing.

Something like below?

Will

--->8

>From 4d9dcb9210c1f37435b6088284e04b6b36ee8c4d Mon Sep 17 00:00:00 2001
From: Will Deacon <will@...nel.org>
Date: Fri, 2 Jul 2021 14:13:28 +0100
Subject: [PATCH] of: Return success from of_dma_set_restricted_buffer() when
 !OF_ADDRESS

When CONFIG_OF_ADDRESS=n, of_dma_set_restricted_buffer() returns -ENODEV
and breaks the boot for sparc[64] machines. Return 0 instead, since the
function is essentially a glorified NOP in this configuration.

Cc: Claire Chang <tientzu@...omium.org>
Cc: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
Reported-by: Guenter Roeck <linux@...ck-us.net>
Suggested-by: Robin Murphy <robin.murphy@....com>
Link: https://lore.kernel.org/r/20210702030807.GA2685166@roeck-us.net
Signed-off-by: Will Deacon <will@...nel.org>
---
 drivers/of/of_private.h | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/of/of_private.h b/drivers/of/of_private.h
index 8fde97565d11..34dd548c5eac 100644
--- a/drivers/of/of_private.h
+++ b/drivers/of/of_private.h
@@ -173,7 +173,8 @@ static inline int of_dma_get_range(struct device_node *np,
 static inline int of_dma_set_restricted_buffer(struct device *dev,
 					       struct device_node *np)
 {
-	return -ENODEV;
+	/* Do nothing, successfully. */
+	return 0;
 }
 #endif
 
-- 
2.32.0.93.g670b81a890-goog