linux-kernel - Re: dma_zalloc_coherent broken with 57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7

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Message-Id: <alpine.LFD.2.21.1803271717580.26440@schleppi>
Date:   Tue, 27 Mar 2018 17:24:10 +0200 (CEST)
From:   Sebastian Ott <sebott@...ux.vnet.ibm.com>
To:     Christoph Hellwig <hch@....de>
cc:     Jesper Nilsson <jesper.nilsson@...s.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-kernel@...r.kernel.org
Subject: Re: dma_zalloc_coherent broken with
 57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7

On Tue, 27 Mar 2018, Christoph Hellwig wrote:

> On Tue, Mar 27, 2018 at 10:12:54AM +0200, Sebastian Ott wrote:
> > Hi,
> > 
> > commit 57bf5a8963f80fb3828c46c3e3a5b2dd790e09a7 broke usage of dma
> > allocations specifying __GFP_ZERO by silently removing that flag.
> > 
> > Why should "the memory returned [] always be zeroed."?
> 
> Because that is what the current implementations do - we always zero
> the memory returned from dma_map_ops.alloc().

What do you mean by current implementations? Arch specific code? At least
on s390 we don't do that. dma-mapping.h doesn't do it either.

Sebastian