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

[Laurentiu Tudor <laurentiu.tudor@nxp.com>]

On 4/14/2020 5:32 PM, Lorenzo Pieralisi wrote:
> On Wed, Mar 25, 2020 at 06:48:55PM +0200, Laurentiu Tudor wrote:
>> Hi Lorenzo,
>>
>> On 3/25/2020 2:51 PM, Lorenzo Pieralisi wrote:
>>> On Thu, Feb 27, 2020 at 12:05:39PM +0200, laurentiu.tudor@nxp.com wrote:
>>>> From: Laurentiu Tudor <laurentiu.tudor@nxp.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@nxp.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
>>
>> 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.
> 
> Actually, what I think you need is of_map_rid() (and an IORT
> equivalent, that I am going to write - generalizing iort_msi_map_rid()).
> 
> Would that be enough to enable IORT "normal" mappings in the MC bus
> named components ?
> 

At a first glance, looks like this could very well fix the ACPI
scenario, but I have some unclarities on the approach:
 * are we going to rely in DT and ACPI generic layers even if these
devices are not published / enumerated through DT or ACPI tables?
 * the firmware manages and provides discrete streamids for the devices
it exposes so there's no translation involved. There's no
   requestor_id / input_id involved but it seems that we would still do
some kind of translation relying for this on the DT/ACPI functions.
 * MC firmware has its own stream_id (e.g. on some chips 0x4000, others
0xf00, so outside the range of stream_ids used for the mc devices)
   while for the devices on this bus, MC allocates stream_ids from a
range (e.g. 0x17 - 0x3f). Is it possible to describe this in the IORT table?
 * Regarding the of_map_rid() use you mentioned, I was planning to
decouple the mc bus from the DT layer by dropping the use of
of_map_rid(), see patch 4.
I briefly glanced over the iort code and spotted this static function:
iort_iommu_xlate(). Wouldn't it also help, of course after making it public?

---
Thanks & Best Regards, Laurentiu