linux-kernel - RFC: ARM && restricted DMA apparently not working

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Message-Id: <20230926175208.9298-1-james.quinlan@broadcom.com>
Date:   Tue, 26 Sep 2023 13:52:05 -0400
From:   Jim Quinlan <james.quinlan@...adcom.com>
To:     Christoph Hellwig <hch@....de>,
        bcm-kernel-feedback-list@...adcom.com, jim2101024@...il.com,
        james.quinlan@...adcom.com
Cc:     Andrew Morton <akpm@...ux-foundation.org>,
        Arnd Bergmann <arnd@...db.de>,
        Christophe Leroy <christophe.leroy@...roup.eu>,
        Eric DeVolder <eric.devolder@...cle.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Jonathan Corbet <corbet@....net>,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Linus Walleij <linus.walleij@...aro.org>,
        linux-arm-kernel@...ts.infradead.org (moderated list:ARM PORT),
        linux-kernel@...r.kernel.org (open list),
        "Mike Rapoport (IBM)" <rppt@...nel.org>,
        Nathan Chancellor <nathan@...nel.org>,
        "Russell King (Oracle)" <rmk+kernel@...linux.org.uk>,
        Sebastian Reichel <sebastian.reichel@...labora.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: RFC: ARM && restricted DMA apparently not working

We've just started using the resticted memory feature (DMA_RESTRICTED_POOL)
which isolates a region for DMA memory for a particular device,
SWIOTLB-style.  This feature works with ARCH=arm64 but does not work on
ARCH=arm unless I apply the commit to select DMA_DIRECT_REMAP.  This seems
to hold from 5.15 to the present.

I've noticed that arm64 selects DMA_DIRECT_REMAP and arm does not and I'm
guessing that there may be a reason for this?

Regards,
Jim Quinlan
Broadcom STB/CM

Jim Quinlan (1):
  ARM: Select DMA_DIRECT_REMAP to fix restricted memory

 arch/arm/Kconfig | 1 +
 1 file changed, 1 insertion(+)


base-commit: 6465e260f48790807eef06b583b38ca9789b6072
-- 
2.17.1


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