linux-kernel - Re: dma_declare_coherent

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Date:   Mon, 28 Jun 2021 14:47:15 -0500
From:   Rob Landley <rob@...dley.net>
To:     Christoph Hellwig <hch@....de>
Cc:     Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>, linux-sh@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: dma_declare_coherent_memory and SuperH

On 6/28/21 11:33 AM, Christoph Hellwig wrote:
> On Mon, Jun 28, 2021 at 09:29:59AM -0500, Rob Landley wrote:
> >> Your plan is to eliminate the ability for non-device-tree boards to do DMA?
>
>> > No.
>
>> Which part of this exchange have I misunderstood?
> 
> The part that there is no easy way out without the device tree
> conversion.

Interesting use of the word "No".

I didn't ask for easy, I asked what needed to be done. What is the patch you
want to apply to kernel/dma so I can see what infrastructure needs to be moved
into arch/sh so it's our problem and not yours.

If a wrapper function has to fake up a temporary device tree snippet to lie to
new DMA infrastructure that refuses to export non-systemd APIs to handle this,
fine. It's still less intrusive than converting EVERY device to a new API on
boards I can't easily regression test. (And hey, if you squint that would be a
little like a partial incremental device tree conversion.)

Rob