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charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org > -----Original Message----- > From: Will Deacon > Sent: Monday, August 9, 2021 8:51 AM > To: Frank Li > Cc: Catalin Marinas ; Zhi Li ; > Shenwei Wang ; Han Xu ; Nitin Garg > ; Jason Liu ; linux-arm- > kernel@lists.infradead.org > Subject: Re: [EXT] Re: The problem about arm64: io: Relax implicit barriers > in default I/O accessors > > Caution: EXT Email > > On Thu, Jul 22, 2021 at 07:14:19PM +0000, Frank Li wrote: > > > > On Wed, Jun 23, 2021 at 03:48:10PM +0000, Frank Li wrote: > > > > > > I think you had a support case open with Arm [1] which I'm not > able > > > to > > > > > > access -- please can you ask them about the two examples above? > > > > > > > > > > Still not get feedback from ARM. > > > > > > > > Just wondering if you were able to solve this without the need to > change > > > > Linux? > > > > > > Sorry for late reply > > > > > > For CCI-500 and 550, ARM removed support for barrier transactions but > CCI- > > > 400 supports barrier transactions. With CCI-400 it is a valid > configuration > > > to have SYSBARDISABLE LOW in Cortex-A processors. This change in Linux > > > kernel is assuming that the SYSBARDISABLE is set to HIGH hence its not > > > correct change for all products having various versions of ARM CCI IP. > > > > > > Frank Li > > > > Deacon: > > > > Did you plan fix this problem by changing dma_wmb()? > > No. As far as I understand this problem, you're driving SYSBARDISABLE > 'low' yet you have your own bus fabric downstream of the CCI which doesn't > respect barrier transactions. Even if we bodge dma_wmb(), store-release to > non-cacheable memory cannot be made to work on your system as you're > effectively putting some of your non-coherent DMA devices into a separate > outer-shareable domain from the CPUs. Does it means the Linux expect all DMA devices in outer-shareable domain instead of system shared domain? Frank > > So you have two options: > > 1. Drive SYSBARDISABLE 'high' so that the CPU handles ordering for you > > - or - > > 2. Quirk Linux so that we patch dma_wmb() when we detect your system at > runtime (so we can extend this in future if we need to emit a > different > sequence for store release) > > (1) is definitely the easiest option if it's possible. > > Will _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel