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

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Message-ID: <20200414143211.GA14905@red-moon.cambridge.arm.com>
Date:   Tue, 14 Apr 2020 15:32:11 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Laurentiu Tudor <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 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@....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
> 
> 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 ?

Thanks,
Lorenzo