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From:   Dan Williams <dan.j.williams@intel.com>
Date:   Wed, 1 Apr 2020 13:26:55 -0700
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Subject: Re: [PATCH v4 11/25] powerpc: Enable the OpenCAPI Persistent Memory
 driver for powernv_defconfig
To:     "Alastair D'Silva" <alastair@d-silva.org>
Cc:     "Aneesh Kumar K . V" <aneesh.kumar@linux.ibm.com>,
        "Oliver O'Halloran" <oohall@gmail.com>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
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        Michael Ellerman <mpe@ellerman.id.au>,
        Frederic Barrat <fbarrat@linux.ibm.com>,
        Andrew Donnellan <ajd@linux.ibm.com>,
        Arnd Bergmann <arnd@arndb.de>,
        Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Vishal Verma <vishal.l.verma@intel.com>,
        Dave Jiang <dave.jiang@intel.com>,
        Ira Weiny <ira.weiny@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>,
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        "David S. Miller" <davem@davemloft.net>,
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On Sun, Mar 29, 2020 at 10:23 PM Alastair D'Silva <alastair@d-silva.org> wrote:
>
> This patch enables the OpenCAPI Persistent Memory driver, as well
> as DAX support, for the 'powernv' defconfig.
>
> DAX is not a strict requirement for the functioning of the driver, but it
> is likely that a user will want to create a DAX device on top of their
> persistent memory device.
>
> Signed-off-by: Alastair D'Silva <alastair@d-silva.org>
> Reviewed-by: Andrew Donnellan <ajd@linux.ibm.com>
> ---
>  arch/powerpc/configs/powernv_defconfig | 5 +++++
>  1 file changed, 5 insertions(+)
>
> diff --git a/arch/powerpc/configs/powernv_defconfig b/arch/powerpc/configs/powernv_defconfig
> index 71749377d164..921d77bbd3d2 100644
> --- a/arch/powerpc/configs/powernv_defconfig
> +++ b/arch/powerpc/configs/powernv_defconfig
> @@ -348,3 +348,8 @@ CONFIG_KVM_BOOK3S_64=m
>  CONFIG_KVM_BOOK3S_64_HV=m
>  CONFIG_VHOST_NET=m
>  CONFIG_PRINTK_TIME=y
> +CONFIG_ZONE_DEVICE=y
> +CONFIG_OCXL_PMEM=m
> +CONFIG_DEV_DAX=m
> +CONFIG_DEV_DAX_PMEM=m
> +CONFIG_FS_DAX=y

These options have dependencies. I think it would better to implement
a top-level configuration question called something like
PERSISTENT_MEMORY_ALL that goes and selects all the bus providers and
infrastructure and lets other defaults follow along. For example,
CONFIG_DEV_DAX could grow a "default LIBNVDIMM" and then
CONFIG_DEV_DAX_PMEM would default on as well. If
CONFIG_PERSISTENT_MEMORY_ALL selected all the bus providers and
ZONE_DEVICE then the Kconfig system could prompt you to where the
dependencies are not satisfied.