linux-kernel - Re: [RFC PATCH 1/4] bus: fsl-mc: add custom .dma

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Message-ID: <20200325125109.GA5430@red-moon.cambridge.arm.com>
Date:   Wed, 25 Mar 2020 12:51:18 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     laurentiu.tudor@....com
Cc:     linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-arm-kernel@...ts.infradead.org, linux-acpi@...r.kernel.org,
        robin.murphy@....com, ard.biesheuvel@...aro.org,
        ioana.ciornei@....com, diana.craciun@....nxp.com, maz@...nel.org,
        jon@...id-run.com, pankaj.bansal@....com, makarand.pawagi@....com,
        calvin.johnson@....com, V.Sethi@....com, cristian.sovaiala@....com,
        Stuart.Yoder@....com, jeremy.linton@....com, joro@...tes.org,
        tglx@...utronix.de, jason@...edaemon.net
Subject: Re: [RFC PATCH 1/4] bus: fsl-mc: add custom .dma_configure
 implementation

On Thu, Feb 27, 2020 at 12:05:39PM +0200, laurentiu.tudor@....com wrote:
> From: Laurentiu Tudor <laurentiu.tudor@....com>
> 
> The devices on this bus are not discovered by way of device tree
> but by queries to the firmware. It makes little sense to trick the
> generic of layer into thinking that these devices are of related so
> that we can get our dma configuration. Instead of doing that, add
> our custom dma configuration implementation.
> 
> Signed-off-by: Laurentiu Tudor <laurentiu.tudor@....com>
> ---
>  drivers/bus/fsl-mc/fsl-mc-bus.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/bus/fsl-mc/fsl-mc-bus.c b/drivers/bus/fsl-mc/fsl-mc-bus.c
> index 36eb25f82c8e..eafaa0e0b906 100644
> --- a/drivers/bus/fsl-mc/fsl-mc-bus.c
> +++ b/drivers/bus/fsl-mc/fsl-mc-bus.c
> @@ -132,11 +132,40 @@ static int fsl_mc_bus_uevent(struct device *dev, struct kobj_uevent_env *env)
>  static int fsl_mc_dma_configure(struct device *dev)
>  {
>  	struct device *dma_dev = dev;
> +	struct iommu_fwspec *fwspec;
> +	const struct iommu_ops *iommu_ops;
> +	struct fsl_mc_device *mc_dev = to_fsl_mc_device(dev);
> +	int ret;
> +	u32 icid;
>  
>  	while (dev_is_fsl_mc(dma_dev))
>  		dma_dev = dma_dev->parent;
>  
> -	return of_dma_configure(dev, dma_dev->of_node, 0);
> +	fwspec = dev_iommu_fwspec_get(dma_dev);
> +	if (!fwspec)
> +		return -ENODEV;
> +	iommu_ops = iommu_ops_from_fwnode(fwspec->iommu_fwnode);
> +	if (!iommu_ops)
> +		return -ENODEV;
> +
> +	ret = iommu_fwspec_init(dev, fwspec->iommu_fwnode, iommu_ops);
> +	if (ret)
> +		return ret;
> +
> +	icid = mc_dev->icid;
> +	ret = iommu_fwspec_add_ids(dev, &icid, 1);

I see. So with this patch we would use the MC named component only to
retrieve the iommu_ops - the streamid are injected directly here
bypassing OF/IORT bindings translations altogether. Am I reading this
code correctly ?

Thanks,
Lorenzo

> +	if (ret)
> +		return ret;
> +
> +	if (!device_iommu_mapped(dev)) {
> +		ret = iommu_probe_device(dev);
> +		if (ret)
> +			return ret;
> +	}
> +
> +	arch_setup_dma_ops(dev, 0, *dma_dev->dma_mask + 1, iommu_ops, true);
> +
> +	return 0;
>  }
>  
>  static ssize_t modalias_show(struct device *dev, struct device_attribute *attr,
> -- 
> 2.17.1
>