linux-kernel - Re: [RFC PATCH 2/2] ACPI/IORT: use swiotlb_dma

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Date:   Wed, 4 Apr 2018 17:01:38 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Wang Dongsheng <dongsheng.wang@...-semitech.com>
Cc:     rjw@...ysocki.net, gregkh@...uxfoundation.org,
        hanjun.guo@...aro.org, sudeep.holla@....com,
        yu.zheng@...-semitech.com, linux-acpi@...r.kernel.org,
        linux-kernel@...r.kernel.org, robin.murphy@....com
Subject: Re: [RFC PATCH 2/2] ACPI/IORT: use swiotlb_dma_ops when smmu probe
 failed

[+cc Robin]

On Thu, Mar 29, 2018 at 03:01:00AM -0700, Wang Dongsheng wrote:
> If SMMU probe failed, master should use swiotlb as dma ops.
> SMMU may probe failed with specified environment, so there
> are not any iommu resources in iommu_device_list.
> 
> The master will always get EPROBE_DEFER from really_probe
> (dma_configure) but in fact SMMU has probe failed. The issue
> causes all of masters failed to be driven.

I added Robin to pick his brain. An alternative would consist
in using a bus notifier to prevent deferred probing once the SMMU
driver probing failed but that seems backwards given that a major
reason to move to deferred probing was to remove the bus notifiers
dependency in the first place.

It seems to me this is both an OF/ACPI issue - it is not an IORT
only problem.

Lorenzo

> Signed-off-by: Wang Dongsheng <dongsheng.wang@...-semitech.com>
> ---
>  drivers/acpi/arm64/iort.c | 39 +++++++++++++++++++++++++++++++++------
>  1 file changed, 33 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> index e2f7bdd..a6f4c27 100644
> --- a/drivers/acpi/arm64/iort.c
> +++ b/drivers/acpi/arm64/iort.c
> @@ -774,17 +774,45 @@ static int arm_smmu_iort_xlate(struct device *dev, u32 streamid,
>  	return ret;
>  }
>  
> -static inline bool iort_iommu_driver_enabled(u8 type)
> +static int iort_check_dev_dl_status(struct device *dev, void *data)
>  {
> +	struct fwnode_handle *fwnode = data;
> +
> +	if (dev->fwnode != fwnode)
> +		return 0;
> +
> +	if (dev->links.status == DL_DEV_PROBE_FAILED)
> +		return -ENODEV;
> +
> +	return -EPROBE_DEFER;
> +}
> +
> +static int iort_iommu_driver_enabled(u8 type, struct fwnode_handle *fwnode)
> +{
> +	bool buildin;
> +	int ret;
> +
>  	switch (type) {
>  	case ACPI_IORT_NODE_SMMU_V3:
> -		return IS_BUILTIN(CONFIG_ARM_SMMU_V3);
> +		buildin = IS_BUILTIN(CONFIG_ARM_SMMU_V3);
> +		break;
>  	case ACPI_IORT_NODE_SMMU:
> -		return IS_BUILTIN(CONFIG_ARM_SMMU);
> +		buildin = IS_BUILTIN(CONFIG_ARM_SMMU);
> +		break;
>  	default:
>  		pr_warn("IORT node type %u does not describe an SMMU\n", type);
> -		return false;
> +		buildin = false;
>  	}
> +
> +	if (!buildin)
> +		return -ENODEV;
> +
> +	ret = bus_for_each_dev(&platform_bus_type, NULL, fwnode,
> +			       iort_check_dev_dl_status);
> +	if (!ret)
> +		return -EPROBE_DEFER;
> +
> +	return ret;
>  }
>  
>  #ifdef CONFIG_IOMMU_API
> @@ -919,8 +947,7 @@ static int iort_iommu_xlate(struct device *dev, struct acpi_iort_node *node,
>  	 */
>  	ops = iommu_ops_from_fwnode(iort_fwnode);
>  	if (!ops)
> -		return iort_iommu_driver_enabled(node->type) ?
> -		       -EPROBE_DEFER : -ENODEV;
> +		return iort_iommu_driver_enabled(node->type, iort_fwnode);
>  
>  	return arm_smmu_iort_xlate(dev, streamid, iort_fwnode, ops);
>  }
> -- 
> 2.7.4
>