linux-kernel - Re: [PATCH v5 1/2] dax: introduce CONFIG_DAX

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Date:   Fri, 29 Sep 2017 16:11:51 +1000
From:   Michael Ellerman <mpe@...erman.id.au>
To:     Dan Williams <dan.j.williams@...el.com>, snitzer@...hat.com
Cc:     linux-nvdimm@...ts.01.org,
        Heiko Carstens <heiko.carstens@...ibm.com>,
        linux-kernel@...r.kernel.org,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        dm-devel@...hat.com, Paul Mackerras <paulus@...ba.org>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Bart Van Assche <Bart.VanAssche@....com>,
        Gerald Schaefer <gerald.schaefer@...ibm.com>
Subject: Re: [PATCH v5 1/2] dax: introduce CONFIG_DAX_DRIVER

Dan Williams <dan.j.williams@...el.com> writes:

> In support of allowing device-mapper to compile out idle/dead code when
> there are no dax providers in the system, introduce the DAX_DRIVER
> symbol. This is selected by all leaf drivers that device-mapper might be
> layered on top. This allows device-mapper to conditionally 'select DAX'
> only when a provider is present.
>
> Cc: Paul Mackerras <paulus@...ba.org>
> Cc: Michael Ellerman <mpe@...erman.id.au>
> Cc: Martin Schwidefsky <schwidefsky@...ibm.com>
> Cc: Heiko Carstens <heiko.carstens@...ibm.com>
> Cc: Gerald Schaefer <gerald.schaefer@...ibm.com>
> Cc: Benjamin Herrenschmidt <benh@...nel.crashing.org>
> Cc: Mike Snitzer <snitzer@...hat.com>
> Cc: Bart Van Assche <Bart.VanAssche@....com>
> Signed-off-by: Dan Williams <dan.j.williams@...el.com>
> ---
>  arch/powerpc/platforms/Kconfig |    1 +
>  drivers/block/Kconfig          |    1 +
>  drivers/dax/Kconfig            |    4 +++-
>  drivers/nvdimm/Kconfig         |    1 +
>  drivers/s390/block/Kconfig     |    1 +
>  5 files changed, 7 insertions(+), 1 deletion(-)
>
> diff --git a/arch/powerpc/platforms/Kconfig b/arch/powerpc/platforms/Kconfig
> index 4fd64d3f5c44..4561340c1f92 100644
> --- a/arch/powerpc/platforms/Kconfig
> +++ b/arch/powerpc/platforms/Kconfig
> @@ -296,6 +296,7 @@ config AXON_RAM
>  	tristate "Axon DDR2 memory device driver"
>  	depends on PPC_IBM_CELL_BLADE && BLOCK
>  	select DAX
> +	select DAX_DRIVER


I would have thought you'd want to replace the select of DAX with
a select of DAX_DRIVER?

With the driver selecting both there's no need for the core to select
DAX, because all the DAX drivers have done it already.

cheers