linux-kernel - Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping attributes

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Date:   Mon, 21 Jan 2019 00:30:46 -0800
From:   Christoph Hellwig <hch@...radead.org>
To:     Laura Abbott <labbott@...hat.com>
Cc:     Christoph Hellwig <hch@...radead.org>,
        Liam Mark <lmark@...eaurora.org>, sumit.semwal@...aro.org,
        arve@...roid.com, tkjos@...roid.com, maco@...roid.com,
        joel@...lfernandes.org, christian@...uner.io,
        devel@...verdev.osuosl.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org, linux-kernel@...r.kernel.org,
        afd@...com, john.stultz@...aro.org
Subject: Re: [PATCH 3/4] dma-buf: add support for mapping with dma mapping
 attributes

On Sat, Jan 19, 2019 at 08:50:41AM -0800, Laura Abbott wrote:
> > And who is going to decide which ones to pass?  And who documents
> > which ones are safe?
> > 
> > I'd much rather have explicit, well documented dma-buf flags that
> > might get translated to the DMA API flags, which are not error checked,
> > not very well documented and way to easy to get wrong.
> > 
> 
> I'm not sure having flags in dma-buf really solves anything
> given drivers can use the attributes directly with dma_map
> anyway, which is what we're looking to do. The intention
> is for the driver creating the dma_buf attachment to have
> the knowledge of which flags to use.

Well, there are very few flags that you can simply use for all calls of
dma_map*.  And given how badly these flags are defined I just don't want
people to add more places where they indirectly use these flags, as
it will be more than enough work to clean up the current mess.

What flag(s) do you want to pass this way, btw?  Maybe that is where
the problem is.