Subject: Re: [PATCH v3 03/24] wfx: add Makefile/Kconfig

From: Jérôme Pouiller <[email-masked]>
Date: Tue, 22 Dec 2020 22:19:52 +0100

On Tuesday 22 December 2020 16:02:38 CET Kalle Valo wrote:
> Jerome Pouiller <[email-masked]> writes:
> 
> > From: Jérôme Pouiller <[email-masked]>
> >
> > Signed-off-by: Jérôme Pouiller <[email-masked]>
> 
> [...]
> 
> > +wfx-$(CONFIG_SPI) += bus_spi.o
> > +wfx-$(subst m,y,$(CONFIG_MMC)) += bus_sdio.o
> 
> Why this subst? And why only for MMC?

CONFIG_SPI is a boolean (y or empty). The both values make senses.

CONFIG_MMC is a tristate (y, m or empty). The substitution above
ensure that bus_sdio.o will included in wfx.ko if CONFIG_MMC is 'm'
("wfx-$(CONFIG_MMC) += bus_sdio.o" wouldn't make the job).

You may want to know what it happens if CONFIG_MMC=m while CONFIG_WFX=y.
This line in Kconfig prevents to compile wfx statically if MMC is a
module:
       depends on MMC || !MMC # do not allow WFX=y if MMC=m

-- 
Jérôme Pouiller