linux-kernel - Re: [PATCH 18/22] mm: mark DEVICE

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Date:   Thu, 13 Jun 2019 19:44:34 +0000
From:   Jason Gunthorpe <jgg@...lanox.com>
To:     Christoph Hellwig <hch@....de>
CC:     Dan Williams <dan.j.williams@...el.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "nouveau@...ts.freedesktop.org" <nouveau@...ts.freedesktop.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "linux-nvdimm@...ts.01.org" <linux-nvdimm@...ts.01.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 18/22] mm: mark DEVICE_PUBLIC as broken

On Thu, Jun 13, 2019 at 11:43:21AM +0200, Christoph Hellwig wrote:
> The code hasn't been used since it was added to the tree, and doesn't
> appear to actually be usable.  Mark it as BROKEN until either a user
> comes along or we finally give up on it.
> 
> Signed-off-by: Christoph Hellwig <hch@....de>
>  mm/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 0d2ba7e1f43e..406fa45e9ecc 100644
> +++ b/mm/Kconfig
> @@ -721,6 +721,7 @@ config DEVICE_PRIVATE
>  config DEVICE_PUBLIC
>  	bool "Addressable device memory (like GPU memory)"
>  	depends on ARCH_HAS_HMM
> +	depends on BROKEN
>  	select HMM
>  	select DEV_PAGEMAP_OPS

This seems a bit harsh, we do have another kconfig that selects this
one today:

config DRM_NOUVEAU_SVM
        bool "(EXPERIMENTAL) Enable SVM (Shared Virtual Memory) support"
        depends on ARCH_HAS_HMM
        depends on DRM_NOUVEAU
        depends on STAGING
        select HMM_MIRROR
        select DEVICE_PRIVATE
        default n
        help
          Say Y here if you want to enable experimental support for
          Shared Virtual Memory (SVM).

Maybe it should be depends on STAGING not broken?

or maybe nouveau_svm doesn't actually need DEVICE_PRIVATE?

Jason