From: Christoph Hellwig <hch@lst.de>
To: Oliver O'Halloran <oohall@gmail.com>
Cc: Alexey Kardashevskiy <aik@ozlabs.ru>,
linuxppc-dev <linuxppc-dev@lists.ozlabs.org>,
Shawn Anastasio <shawn@anastas.io>,
Christoph Hellwig <hch@lst.de>,
Sam Bobroff <sbobroff@linux.ibm.com>
Subject: Re: [PATCH] powerpc/dma: Fix invalid DMA mmap behavior
Date: Thu, 18 Jul 2019 10:49:34 +0200 [thread overview]
Message-ID: <20190718084934.GF24562@lst.de> (raw)
In-Reply-To: <CAOSf1CGA_fDH7aAqRkc4maJUByaX7adGcjyt3cj4KFsMJNnocA@mail.gmail.com>
On Thu, Jul 18, 2019 at 01:45:16PM +1000, Oliver O'Halloran wrote:
> > Other than m68k, mips, and arm64, everybody else that doesn't have
> > ARCH_NO_COHERENT_DMA_MMAP set uses this default implementation, so
> > I assume this behavior is acceptable on those architectures.
>
> It might be acceptable, but there's no reason to use pgport_noncached
> if the platform supports cache-coherent DMA.
>
> Christoph (+cc) made the change so maybe he saw something we're missing.
I always found the forcing of noncached access even for coherent
devices a little odd, but this was inherited from the previous
implementation, which surprised me a bit as the different attributes
are usually problematic even on x86. Let me dig into the history a
bit more, but I suspect the righ fix is to default to cached mappings
for coherent devices.
next prev parent reply other threads:[~2019-07-18 8:56 UTC|newest]
Thread overview: 14+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-07-17 23:54 [PATCH] powerpc/dma: Fix invalid DMA mmap behavior Shawn Anastasio
2019-07-18 2:59 ` Alexey Kardashevskiy
2019-07-18 3:14 ` Shawn Anastasio
2019-07-18 3:45 ` Oliver O'Halloran
2019-07-18 8:49 ` Christoph Hellwig [this message]
2019-07-18 9:52 ` Christoph Hellwig
2019-07-18 19:46 ` Shawn Anastasio
2019-07-19 7:06 ` Christoph Hellwig
2019-07-19 7:36 ` Shawn Anastasio
2019-07-19 11:18 ` Arnd Bergmann
2019-07-22 12:16 ` Michael Ellerman
2019-07-22 19:23 ` Shawn Anastasio
2019-07-22 23:09 ` Michael Ellerman
2019-07-22 2:48 ` Michael Ellerman
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