linux-kernel - Re: [PATCH 1/4] net: sgi: ioc3-eth: don't abuse dma_direct

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Message-ID: <20191031170127.GA8646@lst.de>
Date:   Thu, 31 Oct 2019 18:01:27 +0100
From:   Christoph Hellwig <hch@....de>
To:     Thomas Bogendoerfer <tbogendoerfer@...e.de>
Cc:     Christoph Hellwig <hch@....de>,
        "David S. Miller" <davem@...emloft.net>,
        linux-mips@...r.kernel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] net: sgi: ioc3-eth: don't abuse dma_direct_* calls

On Thu, Oct 31, 2019 at 04:18:17PM +0100, Thomas Bogendoerfer wrote:
> On Thu, 31 Oct 2019 14:15:01 +0100
> Christoph Hellwig <hch@....de> wrote:
> 
> > On Thu, Oct 31, 2019 at 09:54:30AM +0100, Thomas Bogendoerfer wrote:
> > > I didn't want to argue about that. What I'm interested in is a way how 
> > > to allocate dma memory, which is 16kB aligned, via the DMA API ?
> > 
> > You can't.
> 
> So then __get_free_pages() and dma_map_page() is the only way ?

Or dma_alloc_coherent + check alignment + allocate larger and align
yourself.  In practice you'll always get alignmened memory at the
moment, but there is no API gurantee.