linux-kernel - Re: [RFC PATCH] platform: ioremap: Build iomap functions even without HAS

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Message-ID: <20200723094134.0000432d@Huawei.com>
Date:   Thu, 23 Jul 2020 09:41:34 +0100
From:   Jonathan Cameron <Jonathan.Cameron@...wei.com>
To:     David Gow <davidgow@...gle.com>
CC:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jeff Dike <jdike@...toit.com>, <rafael@...nel.org>,
        Logan Gunthorpe <logang@...tatee.com>,
        Richard Weinberger <richard@....at>,
        Brendan Higgins <brendanhiggins@...gle.com>,
        <kunit-dev@...glegroups.com>,
        linux-um <linux-um@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH] platform: ioremap: Build iomap functions even
 without HAS_IOMEM

On Mon, 20 Jul 2020 22:45:28 -0700
David Gow <davidgow@...gle.com> wrote:

> A number of drivers use devm_platform_ioremap_resource(), but do not (or
> did not) explicitly depend on IOMEM[1,2]. Given that the only platform
> without HAS_IOMEM seems to be UML, and it has sufficient stubs for
> devm_platform_ioremap_resource() and its dependencies to build, we can
> remove the HAS_IOMEM requirement here, rather than playing whack-a-mole
> with different drivers which don't try to build against ARCH=um.
> 
> The reason this works at the moment is that stub ioremap and iounmap
> functions were added to UML to support this sort-of thing[3]. This
> particular change doesn't require adding any additional stubs, but there
> is possibly room in the future to stub out the remaining iomem functions
> (or to provide mock implementations for testing), and get rid of
> HAS_IOMEM entirely.
> 
> [1]: https://lkml.org/lkml/2020/6/30/176
> [2]:
> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=1e7468bd9d30a21e059af477106dc5588ae52dff
> [3]:
> https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1405627.html

Hi David,

I don't quite follow why we change when iomap_copy.c is built.
Was this just a case of there not seeming to be any reason to protect it
or is there a direct dependency on something in there that I'm missing?

Otherwise looks good to me.

Jonathan

> 
> Signed-off-by: David Gow <davidgow@...gle.com>
> ---
>  drivers/base/platform.c | 2 --
>  lib/Makefile            | 2 +-
>  2 files changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index c0d0a5490ac6..628dde6675cf 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -61,7 +61,6 @@ struct resource *platform_get_resource(struct platform_device *dev,
>  }
>  EXPORT_SYMBOL_GPL(platform_get_resource);
>  
> -#ifdef CONFIG_HAS_IOMEM
>  /**
>   * devm_platform_get_and_ioremap_resource - call devm_ioremap_resource() for a
>   *					    platform device and get resource
> @@ -135,7 +134,6 @@ devm_platform_ioremap_resource_byname(struct platform_device *pdev,
>  	return devm_ioremap_resource(&pdev->dev, res);
>  }
>  EXPORT_SYMBOL_GPL(devm_platform_ioremap_resource_byname);
> -#endif /* CONFIG_HAS_IOMEM */
>  
>  /**
>   * platform_get_irq_optional - get an optional IRQ for a device
> 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
>