Re: [PATCH v2 08/22] lib: implement Devres ioremap_nopost() interface

[Bjorn Helgaas <helgaas@kernel.org>]

On Mon, Mar 27, 2017 at 10:49:36AM +0100, Lorenzo Pieralisi wrote:
> The introduction of the ioremap_nopost() interface allows
> kernel drivers to map memory through a dedicated kernel
> interface providing non-posted writes semantics.
> 
> Introduce two new functions in the Devres kernel layer and Devres
> documentation:
> 
> - devm_ioremap_nopost()
> - devm_ioremap_nopost_resource()
> 
> so that drivers can make use of devm_* interface to map memory
> regions requiring non-posted writes memory attributes.
> 
> Signed-off-by: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
> Cc: Jonathan Corbet <corbet@lwn.net>
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: Tejun Heo <tj@kernel.org>
> ---
>  Documentation/driver-model/devres.txt |  3 ++
>  include/linux/device.h                |  2 +
>  include/linux/io.h                    |  2 +
>  lib/devres.c                          | 78 +++++++++++++++++++++++++++++++++++
>  4 files changed, 85 insertions(+)
> 
> diff --git a/Documentation/driver-model/devres.txt b/Documentation/driver-model/devres.txt
> index bf34d5b..9991a66 100644
> --- a/Documentation/driver-model/devres.txt
> +++ b/Documentation/driver-model/devres.txt
> @@ -294,7 +294,10 @@ IOMAP
>    devm_ioremap()
>    devm_ioremap_nocache()
>    devm_ioremap_wc()
> +  devm_ioremap_nopost()
>    devm_ioremap_resource() : checks resource, requests memory region, ioremaps
> +  devm_ioremap_nopost_resource() : do devm_ioremap_resource() with nopost
> +				   memory attributes
>    devm_iounmap()
>    pcim_iomap()
>    pcim_iomap_regions()	: do request_region() and iomap() on multiple BARs
> diff --git a/include/linux/device.h b/include/linux/device.h
> index 9ef518a..1dce865 100644
> --- a/include/linux/device.h
> +++ b/include/linux/device.h
> @@ -689,6 +689,8 @@ extern unsigned long devm_get_free_pages(struct device *dev,
>  extern void devm_free_pages(struct device *dev, unsigned long addr);
>  
>  void __iomem *devm_ioremap_resource(struct device *dev, struct resource *res);
> +void __iomem *devm_ioremap_nopost_resource(struct device *dev,
> +					   struct resource *res);
>  
>  /* allows to add/remove a custom action to devres stack */
>  int devm_add_action(struct device *dev, void (*action)(void *), void *data);
> diff --git a/include/linux/io.h b/include/linux/io.h
> index 82ef36e..e34d799 100644
> --- a/include/linux/io.h
> +++ b/include/linux/io.h
> @@ -79,6 +79,8 @@ void __iomem *devm_ioremap_nocache(struct device *dev, resource_size_t offset,
>  				   resource_size_t size);
>  void __iomem *devm_ioremap_wc(struct device *dev, resource_size_t offset,
>  				   resource_size_t size);
> +void __iomem *devm_ioremap_nopost(struct device *dev, resource_size_t offset,
> +				   resource_size_t size);
>  void devm_iounmap(struct device *dev, void __iomem *addr);
>  int check_signature(const volatile void __iomem *io_addr,
>  			const unsigned char *signature, int length);
> diff --git a/lib/devres.c b/lib/devres.c
> index cb1464c..4e05660 100644
> --- a/lib/devres.c
> +++ b/lib/devres.c
> @@ -100,6 +100,34 @@ void __iomem *devm_ioremap_wc(struct device *dev, resource_size_t offset,
>  EXPORT_SYMBOL(devm_ioremap_wc);
>  
>  /**
> + * devm_ioremap_nopost - Managed ioremap_nopost()
> + * @dev: Generic device to remap IO address for
> + * @offset: BUS offset to map

I know this comment was just copied from other devm_ioremap*()
interfaces, but I think it's slightly misleading to call this the "BUS
offset".  That suggests this is a bus address, but it is not.  Maybe
it should be "resource address" or similar?

I propose a separate patch to update the existing comments, followed
by this patch to add this new one.

> + * @size: Size of map
> + *
> + * Managed ioremap_nopost().  Map is automatically unmapped on driver detach.
> + */
> +void __iomem *devm_ioremap_nopost(struct device *dev, resource_size_t offset,
> +			      resource_size_t size)
> +{
> +	void __iomem **ptr, *addr;
> +
> +	ptr = devres_alloc(devm_ioremap_release, sizeof(*ptr), GFP_KERNEL);
> +	if (!ptr)
> +		return NULL;
> +
> +	addr = ioremap_nopost(offset, size);
> +	if (addr) {
> +		*ptr = addr;
> +		devres_add(dev, ptr);
> +	} else
> +		devres_free(ptr);
> +
> +	return addr;
> +}
> +EXPORT_SYMBOL(devm_ioremap_nopost);
> +
> +/**
>   * devm_iounmap - Managed iounmap()
>   * @dev: Generic device to unmap for
>   * @addr: Address to unmap
> @@ -163,6 +191,56 @@ void __iomem *devm_ioremap_resource(struct device *dev, struct resource *res)
>  }
>  EXPORT_SYMBOL(devm_ioremap_resource);
>  
> +/**
> + * devm_ioremap_nopost_resource() - devm_ioremap_resource() nopost version
> + * @dev: generic device to handle the resource for
> + * @res: resource to be handled
> + *
> + * Checks that a resource is a valid memory region, requests the memory
> + * region and ioremaps it with ioremap_nopost() interface.
> + * All operations are managed and will be undone on driver detach.
> + *
> + * Returns a pointer to the remapped memory or an ERR_PTR() encoded error code
> + * on failure. Usage example:
> + *
> + *	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> + *	base = devm_ioremap_nopost_resource(&pdev->dev, res);
> + *	if (IS_ERR(base))
> + *		return PTR_ERR(base);
> + */
> +void __iomem *devm_ioremap_nopost_resource(struct device *dev,
> +					   struct resource *res)
> +{
> +	resource_size_t size;
> +	const char *name;
> +	void __iomem *dest_ptr;
> +
> +	BUG_ON(!dev);
> +
> +	if (!res || resource_type(res) != IORESOURCE_MEM) {
> +		dev_err(dev, "invalid resource\n");
> +		return IOMEM_ERR_PTR(-EINVAL);
> +	}
> +
> +	size = resource_size(res);
> +	name = res->name ?: dev_name(dev);
> +
> +	if (!devm_request_mem_region(dev, res->start, size, name)) {
> +		dev_err(dev, "can't request region for resource %pR\n", res);
> +		return IOMEM_ERR_PTR(-EBUSY);
> +	}
> +
> +	dest_ptr = devm_ioremap_nopost(dev, res->start, size);
> +	if (!dest_ptr) {
> +		dev_err(dev, "ioremap failed for resource %pR\n", res);
> +		devm_release_mem_region(dev, res->start, size);
> +		dest_ptr = IOMEM_ERR_PTR(-ENOMEM);
> +	}
> +
> +	return dest_ptr;
> +}
> +EXPORT_SYMBOL(devm_ioremap_nopost_resource);
> +
>  #ifdef CONFIG_HAS_IOPORT_MAP
>  /*
>   * Generic iomap devres
> -- 
> 2.10.0
>