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Date:   Tue, 4 Apr 2017 12:24:50 +0100
From:   Robin Murphy <robin.murphy@....com>
To:     Sricharan R <sricharan@...eaurora.org>, will.deacon@....com,
        joro@...tes.org, lorenzo.pieralisi@....com,
        iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, m.szyprowski@...sung.com,
        bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-acpi@...r.kernel.org, tn@...ihalf.com, hanjun.guo@...aro.org,
        okaya@...eaurora.org, robh+dt@...nel.org, frowand.list@...il.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        sudeep.holla@....com, rjw@...ysocki.net, lenb@...nel.org,
        catalin.marinas@....com, arnd@...db.de, linux-arch@...r.kernel.org,
        gregkh@...uxfoundation.org
Subject: Re: [PATCH V10 08/12] iommu: of: Handle IOMMU lookup failure with
 deferred probing or error

On 04/04/17 11:18, Sricharan R wrote:
> From: Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
> 
> Failures to look up an IOMMU when parsing the DT iommus property need to
> be handled separately from the .of_xlate() failures to support deferred
> probing.
> 
> The lack of a registered IOMMU can be caused by the lack of a driver for
> the IOMMU, the IOMMU device probe not having been performed yet, having
> been deferred, or having failed.
> 
> The first case occurs when the device tree describes the bus master and
> IOMMU topology correctly but no device driver exists for the IOMMU yet
> or the device driver has not been compiled in. Return NULL, the caller
> will configure the device without an IOMMU.
> 
> The second and third cases are handled by deferring the probe of the bus
> master device which will eventually get reprobed after the IOMMU.
> 
> The last case is currently handled by deferring the probe of the bus
> master device as well. A mechanism to either configure the bus master
> device without an IOMMU or to fail the bus master device probe depending
> on whether the IOMMU is optional or mandatory would be a good
> enhancement.

Reviewed-by: Robin Murphy <robin.murphy@....com>

> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Signed-off-by: Laurent Pichart <laurent.pinchart+renesas@...asonboard.com>
> Signed-off-by: Sricharan R <sricharan@...eaurora.org>
> ---
>  drivers/base/dma-mapping.c | 5 +++--
>  drivers/iommu/of_iommu.c   | 4 ++--
>  drivers/of/device.c        | 7 ++++++-
>  include/linux/of_device.h  | 9 ++++++---
>  4 files changed, 17 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c
> index 449b948..82bd45c 100644
> --- a/drivers/base/dma-mapping.c
> +++ b/drivers/base/dma-mapping.c
> @@ -353,6 +353,7 @@ int dma_configure(struct device *dev)
>  {
>  	struct device *bridge = NULL, *dma_dev = dev;
>  	enum dev_dma_attr attr;
> +	int ret = 0;
>  
>  	if (dev_is_pci(dev)) {
>  		bridge = pci_get_host_bridge_device(to_pci_dev(dev));
> @@ -363,7 +364,7 @@ int dma_configure(struct device *dev)
>  	}
>  
>  	if (dma_dev->of_node) {
> -		of_dma_configure(dev, dma_dev->of_node);
> +		ret = of_dma_configure(dev, dma_dev->of_node);
>  	} else if (has_acpi_companion(dma_dev)) {
>  		attr = acpi_get_dma_attr(to_acpi_device_node(dma_dev->fwnode));
>  		if (attr != DEV_DMA_NOT_SUPPORTED)
> @@ -373,7 +374,7 @@ int dma_configure(struct device *dev)
>  	if (bridge)
>  		pci_put_host_bridge_device(bridge);
>  
> -	return 0;
> +	return ret;
>  }
>  
>  void dma_deconfigure(struct device *dev)
> diff --git a/drivers/iommu/of_iommu.c b/drivers/iommu/of_iommu.c
> index c8be889..9f44ee8 100644
> --- a/drivers/iommu/of_iommu.c
> +++ b/drivers/iommu/of_iommu.c
> @@ -236,7 +236,7 @@ const struct iommu_ops *of_iommu_configure(struct device *dev,
>  			ops = ERR_PTR(err);
>  	}
>  
> -	return IS_ERR(ops) ? NULL : ops;
> +	return ops;
>  }
>  
>  static int __init of_iommu_init(void)
> @@ -247,7 +247,7 @@ static int __init of_iommu_init(void)
>  	for_each_matching_node_and_match(np, matches, &match) {
>  		const of_iommu_init_fn init_fn = match->data;
>  
> -		if (init_fn(np))
> +		if (init_fn && init_fn(np))
>  			pr_err("Failed to initialise IOMMU %s\n",
>  				of_node_full_name(np));
>  	}
> diff --git a/drivers/of/device.c b/drivers/of/device.c
> index c2ae6bb..bea8aec 100644
> --- a/drivers/of/device.c
> +++ b/drivers/of/device.c
> @@ -82,7 +82,7 @@ int of_device_add(struct platform_device *ofdev)
>   * can use a platform bus notifier and handle BUS_NOTIFY_ADD_DEVICE events
>   * to fix up DMA configuration.
>   */
> -void of_dma_configure(struct device *dev, struct device_node *np)
> +int of_dma_configure(struct device *dev, struct device_node *np)
>  {
>  	u64 dma_addr, paddr, size;
>  	int ret;
> @@ -129,10 +129,15 @@ void of_dma_configure(struct device *dev, struct device_node *np)
>  		coherent ? " " : " not ");
>  
>  	iommu = of_iommu_configure(dev, np);
> +	if (IS_ERR(iommu))
> +		return PTR_ERR(iommu);
> +
>  	dev_dbg(dev, "device is%sbehind an iommu\n",
>  		iommu ? " " : " not ");
>  
>  	arch_setup_dma_ops(dev, dma_addr, size, iommu, coherent);
> +
> +	return 0;
>  }
>  EXPORT_SYMBOL_GPL(of_dma_configure);
>  
> diff --git a/include/linux/of_device.h b/include/linux/of_device.h
> index af98455..2cacdd8 100644
> --- a/include/linux/of_device.h
> +++ b/include/linux/of_device.h
> @@ -55,7 +55,7 @@ static inline struct device_node *of_cpu_device_node_get(int cpu)
>  	return of_node_get(cpu_dev->of_node);
>  }
>  
> -void of_dma_configure(struct device *dev, struct device_node *np);
> +int of_dma_configure(struct device *dev, struct device_node *np);
>  void of_dma_deconfigure(struct device *dev);
>  #else /* CONFIG_OF */
>  
> @@ -104,8 +104,11 @@ static inline struct device_node *of_cpu_device_node_get(int cpu)
>  {
>  	return NULL;
>  }
> -static inline void of_dma_configure(struct device *dev, struct device_node *np)
> -{}
> +
> +static inline int of_dma_configure(struct device *dev, struct device_node *np)
> +{
> +	return 0;
> +}
>  static inline void of_dma_deconfigure(struct device *dev)
>  {}
>  #endif /* CONFIG_OF */
> 

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