linux-kernel - Re: [PATCH] iio: adc: Specify IOMEM dependency for adi-axi-adc driver

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Message-ID: <CABVgOSnOo4iauOBGpJUZ4NRihCUU-1vue8hajZTCKAcH98_Lrw@mail.gmail.com>
Date:   Wed, 1 Jul 2020 11:04:42 +0800
From:   David Gow <davidgow@...gle.com>
To:     Jonathan Cameron <Jonathan.Cameron@...wei.com>
Cc:     Jonathan Cameron <jic23@...nel.org>,
        Michael Hennerich <michael.hennerich@...log.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Alexandru Ardelean <alexandru.ardelean@...log.com>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        linux-iio@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] iio: adc: Specify IOMEM dependency for adi-axi-adc driver

On Tue, Jun 30, 2020 at 6:07 PM Jonathan Cameron
<Jonathan.Cameron@...wei.com> wrote:
>
> On Tue, 30 Jun 2020 00:05:52 -0700
> David Gow <davidgow@...gle.com> wrote:
>
> > The Analog Devices AXI ADC driver uses the devm_ioremap_resource
> > function, but does not specify a dependency on IOMEM in Kconfig. This
> > causes a build failure on architectures without IOMEM, for example, UML
> > (notably with make allyesconfig).
> >
> > Fix this by making CONFIG_ADI_AXI_ADC depend on CONFIG_IOMEM.
> >
> > Signed-off-by: David Gow <davidgow@...gle.com>
> Hi David,
>
> Could you confirm what the build error is?  I thought the stubs added in
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1bcbfbfdeb
> were meant to allow us to avoid having lots of depends on IOMEM lines for the
> few architectures who don't support it.

No worries:
/usr/bin/ld: drivers/iio/adc/adi-axi-adc.o: in function `adi_axi_adc_probe':
torvalds-linux/drivers/iio/adc/adi-axi-adc.c:415: undefined reference
to `devm_platform_ioremap_resource'

Alas, the devm_platform_ioremap_resource function isn't handled by the
UML stubs: it all seems to be in drivers/base/platform.c and
lib/devres.c, behind #ifdef HAS_IOMEM.

In any case, improving IOMEM support for UML (at least for the KUnit
test case, which is my use case) is something I'd like to do. There
are only three drivers[1,2] upstream at the moment which fail to build
as-is, though, so it seemed worth trying to fix them in the meantime.
That being said, I tried just getting rid of the few #ifdef HAS_IOMEMs
around the various devm_*_ioremap functions, and everything seems to
be working... So maybe that's a false dependency given the various
stubs (at least on UML). I used this (hideously hacky) patch:

diff --git a/drivers/base/platform.c b/drivers/base/platform.c
index c0d0a5490ac6..b6f08c88e2b6 100644
--- a/drivers/base/platform.c
+++ b/drivers/base/platform.c
@@ -61,7 +61,7 @@ struct resource *platform_get_resource(struct
platform_device *dev,
}
EXPORT_SYMBOL_GPL(platform_get_resource);

-#ifdef CONFIG_HAS_IOMEM
+#if 1//def CONFIG_HAS_IOMEM
/**
 * devm_platform_get_and_ioremap_resource - call devm_ioremap_resource() for a
 *                                         platform device and get resource
diff --git a/lib/Makefile b/lib/Makefile
index b1c42c10073b..35c21af33b93 100644
--- a/lib/Makefile
+++ b/lib/Makefile
@@ -115,7 +115,7 @@ obj-y += math/ crypto/

obj-$(CONFIG_GENERIC_IOMAP) += iomap.o
obj-$(CONFIG_GENERIC_PCI_IOMAP) += pci_iomap.o
-obj-$(CONFIG_HAS_IOMEM) += iomap_copy.o devres.o
+obj-y += iomap_copy.o devres.o
obj-$(CONFIG_CHECK_SIGNATURE) += check_signature.o
obj-$(CONFIG_DEBUG_LOCKING_API_SELFTESTS) += locking-selftest.o

---

If this seems to work more broadly, I may try to clean it up and post
it for broader review.

Cheers,
-- David