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Date:   Wed, 15 Apr 2020 17:04:25 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To:     Laurentiu Tudor <laurentiu.tudor@nxp.com>
Cc:     linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
        linux-arm-kernel@lists.infradead.org, linux-acpi@vger.kernel.org,
        robin.murphy@arm.com, ard.biesheuvel@linaro.org,
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        calvin.johnson@nxp.com, V.Sethi@nxp.com, cristian.sovaiala@nxp.com,
        Stuart.Yoder@arm.com, jeremy.linton@arm.com, joro@8bytes.org,
        tglx@linutronix.de, jason@lakedaemon.net
Subject: Re: [RFC PATCH 1/4] bus: fsl-mc: add custom .dma_configure
 implementation
Message-ID: <20200415160425.GA6436@e121166-lin.cambridge.arm.com>
References: <20200227100542.13819-1-laurentiu.tudor@nxp.com>
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 <499fbf9a-416f-d7c7-0655-881d92138a6c@nxp.com>
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On Wed, Apr 15, 2020 at 06:44:37PM +0300, Laurentiu Tudor wrote:
> 
> 
> 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?

Guys I have lost you honestly. I don't understand what you really need
to do with DT and ACPI here. Are they needed to describe what you need
or not ? If the MC dma configure function does not need any DT/ACPI
bindings that's fine by me, I don't understand though why you are still
asking how to represent MC in ACPI then, what for.

Can you talk between *yourselves* please and decide what you need ?

What's the problem ?

Thanks,
Lorenzo