From: Christoph Hellwig <hch@lst.de>
To: Linus Walleij <linus.walleij@linaro.org>
Cc: Jim Quinlan <james.quinlan@broadcom.com>,
Christoph Hellwig <hch@lst.de>,
bcm-kernel-feedback-list@broadcom.com, jim2101024@gmail.com,
Russell King <linux@armlinux.org.uk>,
Arnd Bergmann <arnd@arndb.de>,
Geert Uytterhoeven <geert+renesas@glider.be>,
"Russell King (Oracle)" <rmk+kernel@armlinux.org.uk>,
Andrew Morton <akpm@linux-foundation.org>,
Jonathan Corbet <corbet@lwn.net>,
Thomas Gleixner <tglx@linutronix.de>,
Sebastian Reichel <sebastian.reichel@collabora.com>,
"Mike Rapoport (IBM)" <rppt@kernel.org>,
Eric DeVolder <eric.devolder@oracle.com>,
Nathan Chancellor <nathan@kernel.org>,
"Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
Christophe Leroy <christophe.leroy@csgroup.eu>,
"moderated list:ARM PORT" <linux-arm-kernel@lists.infradead.org>,
open list <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v1 1/1] ARM: Select DMA_DIRECT_REMAP to fix restricted DMA
Date: Mon, 2 Oct 2023 08:16:28 +0200 [thread overview]
Message-ID: <20231002061628.GC911@lst.de> (raw)
In-Reply-To: <CACRpkdYGPpUUCqmJLT4t+6CNOOmRAh_vYPSPK1SWy+tNycnSqQ@mail.gmail.com>
On Thu, Sep 28, 2023 at 01:10:27AM +0200, Linus Walleij wrote:
> (...)
> > + select DMA_DIRECT_REMAP
>
> Christoph invented that symbol so he can certainly
> explain what is missing to use this on ARM.
>
> This looks weird to me, because:
> > git grep atomic_pool_init
> arch/arm/mm/dma-mapping.c:static int __init atomic_pool_init(void)
> kernel/dma/pool.c:static int __init dma_atomic_pool_init(void)
>
> Now you have two atomic DMA pools in the kernel,
> and a lot more than that is duplicated. I'm amazed that it
> compiles at all.
>
> Clearly if you want to do this, surely the ARM-specific
> arch/arm/mm/dma-mapping.c and arch/arm/mm/dma-mapping-nommu.c
> needs to be removed at the same time?
>
> However I don't think it's that simple, because Christoph would surely
> had done this a long time ago if it was that simple.
Yes, DMA_DIRECT_REMAP should only be used for platforms using the
generic generic remap that plus straight into dma-direct and
bypasses arch_dma_alloc.
ARM first needs support to directly set the uncached/wc bits on
the direct mapping for CMA, which should be fairly simple but require
wide spread testing.
I'd be happy to work with anyone who wants to look into this.
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next prev parent reply other threads:[~2023-10-02 6:17 UTC|newest]
Thread overview: 25+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-09-26 17:52 RFC: ARM && restricted DMA apparently not working Jim Quinlan
2023-09-26 17:52 ` [PATCH v1 1/1] ARM: Select DMA_DIRECT_REMAP to fix restricted DMA Jim Quinlan
2023-09-27 7:13 ` kernel test robot
2023-09-27 23:10 ` Linus Walleij
2023-09-28 12:07 ` Jim Quinlan
2023-09-28 13:09 ` Jim Quinlan
2023-09-28 13:32 ` Arnd Bergmann
2023-09-28 14:00 ` Jim Quinlan
2023-09-28 14:01 ` Jim Quinlan
2023-09-28 15:16 ` Arnd Bergmann
2023-09-28 15:33 ` Robin Murphy
2023-09-28 16:20 ` Arnd Bergmann
2023-09-29 19:24 ` Jim Quinlan
2023-09-29 19:52 ` Arnd Bergmann
2023-09-29 21:13 ` Jim Quinlan
2023-10-01 12:48 ` Jim Quinlan
2023-09-28 15:47 ` Robin Murphy
2023-10-02 12:33 ` Jim Quinlan
2023-10-02 15:08 ` Robin Murphy
2023-10-02 6:16 ` Christoph Hellwig [this message]
2023-10-05 17:53 ` Jim Quinlan
2023-10-06 7:40 ` Christoph Hellwig
2023-10-20 8:16 ` Marek Szyprowski
2023-10-23 6:16 ` Christoph Hellwig
2023-09-28 16:24 ` Christophe Leroy
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