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

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Message-Id: <20191031.121546.1075325111948179622.davem@davemloft.net>
Date:   Thu, 31 Oct 2019 12:15:46 -0700 (PDT)
From:   David Miller <davem@...emloft.net>
To:     tbogendoerfer@...e.de
Cc:     hch@....de, 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

From: Thomas Bogendoerfer <tbogendoerfer@...e.de>
Date: Thu, 31 Oct 2019 16:18:17 +0100

> 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 ?
> 
> BTW I've successful tested your patches on an 8 CPU Origin 2k.

Nope, it is not the only way.

Allocate a (SIZE*2)-1 sized piece of DMA memory and align the
resulting CPU pointer and DMA address as needed.