Re: [RFC PATCH 1/4] bus: fsl-mc: add custom .dma_configure implementation

[Laurentiu Tudor]

Hi Lorenzo,

On 3/25/2020 2:51 PM, Lorenzo Pieralisi wrote:
> On Thu, Feb 27, 2020 at 12:05:39PM +0200, laurentiu.tudor@xxxxxxx wrote:
>> From: Laurentiu Tudor <laurentiu.tudor@xxxxxxx>
>>
>> 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@xxxxxxx>
>> ---
>>  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

Right. I'd also add that the implementation tries to follow the existing
standard .dma_configure implementations, e.g. of_dma_configure +
of_iommu_configure. I'd also note that similarly to the ACPI case, this
MC FW device is probed as a platform device in the DT scenario, binding
here [1].
A similar approach is used for the retrieval of the msi irq domain, see
following patch.

> - the streamid are injected directly here bypassing OF/IORT bindings translations altogether. 

Actually I've submitted a v2 [2] that calls into .of_xlate() to allow
the smmu driver to do some processing on the raw streamid coming from
the firmware. I have not yet tested this with ACPI but expect it to
work, however, it's debatable how valid is this approach in the context
of ACPI.

> Am I reading this code correctly ?

Yes. Thanks for taking the time.

[1]
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/misc/fsl,qoriq-mc.txt
[2] https://www.spinics.net/lists/arm-kernel/msg794757.html

---
Best Regards, Laurentiu

> 
>> +	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
>>