[EXT] Re: The problem about arm64: io: Relax implicit barriers in default I/O accessors

[Frank Li]

> -----Original Message-----
> From: Frank Li
> Sent: Thursday, July 15, 2021 10:54 AM
> To: Will Deacon <will at kernel.org>
> Cc: Catalin Marinas <catalin.marinas at arm.com>; Zhi Li <lznuaa at gmail.com>;
> Shenwei Wang <shenwei.wang at nxp.com>; Han Xu <han.xu at nxp.com>; Nitin Garg
> <nitin.garg at nxp.com>; Jason Liu <jason.hui.liu at nxp.com>; linux-arm-
> kernel at lists.infradead.org
> Subject: RE: [EXT] Re: The problem about arm64: io: Relax implicit barriers
> in default I/O accessors
> 
> 
> 
> > -----Original Message-----
> > From: Will Deacon <will at kernel.org>
> > Sent: Tuesday, July 6, 2021 12:11 PM
> > To: Frank Li <frank.li at nxp.com>
> > Cc: Catalin Marinas <catalin.marinas at arm.com>; Zhi Li <lznuaa at gmail.com>;
> > Shenwei Wang <shenwei.wang at nxp.com>; Han Xu <han.xu at nxp.com>; Nitin Garg
> > <nitin.garg at nxp.com>; Jason Liu <jason.hui.liu at nxp.com>; linux-arm-
> > kernel at lists.infradead.org
> > Subject: Re: [EXT] Re: The problem about arm64: io: Relax implicit
> barriers
> > in default I/O accessors
> >
> > Caution: EXT Email
> >
> > Hi Frank,
> >
> > 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()?

Frank Li
> 
> >
> > Cheers,
> >
> > Will