Re: [PATCH v9 4/5] iommu/arm-smmu: Add the device_link between masters and smmu

[Robin Murphy <robin.murphy@arm.com>]

On 13/03/18 08:55, Vivek Gautam wrote:
> From: Sricharan R <sricharan@codeaurora.org>
> 
> Finally add the device link between the master device and
> smmu, so that the smmu gets runtime enabled/disabled only when the
> master needs it. This is done from add_device callback which gets
> called once when the master is added to the smmu.
> 
> Signed-off-by: Sricharan R <sricharan@codeaurora.org>
> Signed-off-by: Vivek Gautam <vivek.gautam@codeaurora.org>
> Reviewed-by: Tomasz Figa <tfiga@chromium.org>
> ---
>   drivers/iommu/arm-smmu.c | 29 +++++++++++++++++++++++++++++
>   1 file changed, 29 insertions(+)
> 
> diff --git a/drivers/iommu/arm-smmu.c b/drivers/iommu/arm-smmu.c
> index 56a04ae80bf3..64953ff2281f 100644
> --- a/drivers/iommu/arm-smmu.c
> +++ b/drivers/iommu/arm-smmu.c
> @@ -1460,10 +1460,31 @@ static int arm_smmu_add_device(struct device *dev)
>   
>   	iommu_device_link(&smmu->iommu, dev);
>   
> +	if (pm_runtime_enabled(smmu->dev)) {
> +		struct device_link *link;
> +
> +		/*
> +		 * Establish the link between smmu and master, so that the
> +		 * smmu gets runtime enabled/disabled as per the master's
> +		 * needs.
> +		 */
> +		link = device_link_add(dev, smmu->dev, DL_FLAG_PM_RUNTIME);
> +		if (!link) {

FWIW, given that we don't really care about link itself, I'd be quite 
happy to simplify that lot down to:

	if (pm_runtime_enabled(smmu_dev) &&
	    !device_link_add(dev, smmu->dev, DL_FLAG_PM_RUNTIME)) {

> +			dev_warn(smmu->dev,
> +				 "Unable to add link to the consumer %s\n",
> +				 dev_name(dev));

(side note: since device_link_add() already prints a message on success, 
maybe it could print its own failure message too?)

Robin.

> +			ret = -ENODEV;
> +			goto out_unlink;
> +		}
> +	}
> +
>   	arm_smmu_rpm_put(smmu);
>   
>   	return 0;
>   
> +out_unlink:
> +	iommu_device_unlink(&smmu->iommu, dev);
> +	arm_smmu_master_free_smes(fwspec);
>   out_rpm_put:
>   	arm_smmu_rpm_put(smmu);
>   out_cfg_free:
> @@ -1486,6 +1507,14 @@ static void arm_smmu_remove_device(struct device *dev)
>   	cfg  = fwspec->iommu_priv;
>   	smmu = cfg->smmu;
>   
> +	if (pm_runtime_enabled(smmu->dev)) {
> +		struct device_link *link;
> +
> +		link = device_link_find(dev, smmu->dev);
> +		if (link)
> +			device_link_del(link);
> +	}
> +
>   	ret = arm_smmu_rpm_get(smmu);
>   	if (ret < 0)
>   		return;
>