netdev - Re: [PATCH 1/4] dma-mapping: add a new dma_need

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Message-ID: <20200706194227.vfhv5o4lporxjxmq@bsd-mbp.dhcp.thefacebook.com>
Date:   Mon, 6 Jul 2020 12:42:27 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Björn Töpel <bjorn.topel@...el.com>,
        Magnus Karlsson <magnus.karlsson@...el.com>,
        iommu@...ts.linux-foundation.org, netdev@...r.kernel.org,
        bpf@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/4] dma-mapping: add a new dma_need_sync API

On Mon, Jun 29, 2020 at 03:03:56PM +0200, Christoph Hellwig wrote:
> Add a new API to check if calls to dma_sync_single_for_{device,cpu} are
> required for a given DMA streaming mapping.
> 
> +::
> +
> +	bool
> +	dma_need_sync(struct device *dev, dma_addr_t dma_addr);
> +
> +Returns %true if dma_sync_single_for_{device,cpu} calls are required to
> +transfer memory ownership.  Returns %false if those calls can be skipped.

Hi Christoph -

Thie call above is for a specific dma_addr.  For correctness, would I
need to check every addr, or can I assume that for a specific memory
type (pages returned from malloc), that the answer would be identical?
-- 
Jonathan