linux-kernel - Re: [RFC PATCH] xen/gntdev: Stop abusing DT of_dma

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Message-ID: <e898c025-32a7-1d2c-3501-c99556f7cdd4@arm.com>
Date:   Thu, 26 Sep 2019 10:49:59 +0100
From:   Julien Grall <julien.grall@....com>
To:     Rob Herring <robh@...nel.org>,
        Oleksandr Andrushchenko <oleksandr_andrushchenko@...m.com>,
        Boris Ostrovsky <boris.ostrovsky@...cle.com>
Cc:     linux-kernel@...r.kernel.org, Robin Murphy <robin.murphy@....com>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Juergen Gross <jgross@...e.com>,
        Stefano Stabellini <sstabellini@...nel.org>,
        xen-devel@...ts.xenproject.org
Subject: Re: [RFC PATCH] xen/gntdev: Stop abusing DT of_dma_configure API

Hi Rob,

On 9/25/19 10:50 PM, Rob Herring wrote:
> As the comment says, this isn't a DT based device. of_dma_configure()
> is going to stop allowing a NULL DT node, so this needs to be fixed.

And this can't work on arch not selecting CONFIG_OF and can select 
CONFIG_XEN_GRANT_DMA_ALLOC.

We are lucky enough on x86 because, AFAICT, arch_setup_dma_ops is just a 
nop.

> 
> Not sure exactly what setup besides arch_setup_dma_ops is needed...

We probably want to update dma_mask, coherent_dma_mask and dma_pfn_offset.

Also, while look at of_configure_dma, I noticed that we consider the DMA 
will not be coherent for the grant-table. Oleksandr, do you know why 
they can't be coherent?

Cheers,

-- 
Julien Grall