linux-kernel - Re: [PATCH 1/1] Drivers: hv: vmbus: Rework use of DMA_BIT

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Date:   Mon, 7 Feb 2022 17:56:10 +0000
From:   Wei Liu <wei.liu@...nel.org>
To:     "Michael Kelley (LINUX)" <mikelley@...rosoft.com>
Cc:     Nathan Chancellor <nathan@...nel.org>,
        KY Srinivasan <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        "wei.liu@...nel.org" <wei.liu@...nel.org>,
        Tianyu Lan <Tianyu.Lan@...rosoft.com>,
        Long Li <longli@...rosoft.com>,
        "ndesaulniers@...gle.com" <ndesaulniers@...gle.com>,
        "vt@...linux.org" <vt@...linux.org>,
        "kuba@...nel.org" <kuba@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-hyperv@...r.kernel.org" <linux-hyperv@...r.kernel.org>,
        "llvm@...ts.linux.dev" <llvm@...ts.linux.dev>
Subject: Re: [PATCH 1/1] Drivers: hv: vmbus: Rework use of DMA_BIT_MASK(64)

On Mon, Feb 07, 2022 at 02:42:31AM +0000, Michael Kelley (LINUX) wrote:
> From: Nathan Chancellor <nathan@...nel.org> Sent: Sunday, February 6, 2022 5:38 PM
> > 
> > Hi Michael,
> > 
> > On Sun, Feb 06, 2022 at 11:36:56AM -0800, Michael Kelley wrote:
> > > Using DMA_BIT_MASK(64) as an initializer for a global variable
> > > causes problems with Clang 12.0.1. The compiler doesn't understand
> > > that value 64 is excluded from the shift at compile time, resulting
> > > in a build error.
> > >
> > > While this is a compiler problem, avoid the issue by setting up
> > > the dma_mask memory as part of struct hv_device, and initialize
> > > it using dma_set_mask().
> > >
> > > Reported-by: Nathan Chancellor <nathan@...nel.org>
> > > Reported-by: Vitaly Chikunov <vt@...linux.org>
> > > Reported-by: Jakub Kicinski <kuba@...nel.org>
> > > Fixes: 743b237c3a7b ("scsi: storvsc: Add Isolation VM support for storvsc driver")
> > > Signed-off-by: Michael Kelley <mikelley@...rosoft.com>
> > 
> > Thanks a lot for working around this. I am hoping that this will be
> > fixed in clang soon, as it is high priority on our list of issues to
> > fix. Once it has been fixed, we should be able to undo this workaround
> > in one way or another.
> 
> FWIW, the new code is as good a solution as the old code.  The new code
> also follows some existing patterns, such as with struct platform_device.
> As such, I don't think of this as a workaround that needs to be undone
> in the future.
> 

Yes indeed.

Patch applied to hyperv-fixes. Thanks.