RE: [PATCH 1/3 v4] drivers/bus: Added Freescale Management Complex APIs

[Stuart Yoder]

> -----Original Message-----
> From: Alexander Graf [mailto:agraf@xxxxxxx]
> Sent: Thursday, November 27, 2014 10:14 AM
> To: Rivera Jose-B46482; gregkh@xxxxxxxxxxxxxxxxxxx; arnd@xxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Cc: Yoder Stuart-B08248; Phillips Kim-R1AAHA; Wood Scott-B07421; Hamciuc Bogdan-BHAMCIU1; Marginean
> Alexandru-R89243; Thorpe Geoff-R01361; Sharma Bhupesh-B45370; Erez Nir-RM30794; Schmitt Richard-B43082
> Subject: Re: [PATCH 1/3 v4] drivers/bus: Added Freescale Management Complex APIs
> 
> 
> 
> On 13.11.14 18:54, J. German Rivera wrote:
> > APIs to access the Management Complex (MC) hardware
> > module of Freescale LS2 SoCs. This patch includes
> > APIs to check the MC firmware version and to manipulate
> > DPRC objects in the MC.
> >
> > Signed-off-by: J. German Rivera <German.Rivera@xxxxxxxxxxxxx>
> > Signed-off-by: Stuart Yoder <stuart.yoder@xxxxxxxxxxxxx>
> 
> [...]
> 
> > +/**
> > + * Creates an MC I/O object
> > + *
> > + * @dev: device to be associated with the MC I/O object
> > + * @mc_portal_phys_addr: physical address of the MC portal to use
> > + * @mc_portal_size: size in bytes of the MC portal
> > + * @flags: flags for the new MC I/O object
> > + * @new_mc_io: Area to return pointer to newly created MC I/O object
> > + *
> > + * Returns '0' on Success; Error code otherwise.
> > + */
> > +int __must_check fsl_create_mc_io(struct device *dev,
> > +				  phys_addr_t mc_portal_phys_addr,
> > +				  uint32_t mc_portal_size,
> > +				  uint32_t flags, struct fsl_mc_io **new_mc_io)
> > +{
> > +	struct fsl_mc_io *mc_io;
> > +	void __iomem *mc_portal_virt_addr;
> > +	struct resource *res;
> > +
> > +	mc_io = devm_kzalloc(dev, sizeof(*mc_io), GFP_KERNEL);
> > +	if (mc_io == NULL)
> > +		return -ENOMEM;
> > +
> > +	mc_io->dev = dev;
> > +	mc_io->flags = flags;
> > +	mc_io->portal_phys_addr = mc_portal_phys_addr;
> > +	mc_io->portal_size = mc_portal_size;
> > +	res = devm_request_mem_region(dev,
> > +				      mc_portal_phys_addr,
> > +				      mc_portal_size,
> > +				      "mc_portal");
> > +	if (res == NULL) {
> > +		dev_err(dev,
> > +			"devm_request_mem_region failed for MC portal %#llx\n",
> > +			mc_portal_phys_addr);
> > +		return -EBUSY;
> > +	}
> > +
> > +	mc_portal_virt_addr = devm_ioremap_nocache(dev,
> > +						   mc_portal_phys_addr,
> > +						   mc_portal_size);
> 
> While I can't complain about the device itself, I will note that I think
> it's a pretty bad design decision to expose actual host physical
> addresses in the protocol.

I tend to agree.  I'll look into creating a proposed change to the architecture
to have the MC communicate a physical offset of some kind.

> Basically this means that you won't be able to pass a full MC complex
> into a guest, even if you could virtualize IRQ and DMA access unless you
> map it at the exact same location as the host's MC complex.

Right.  But is that really an issue in practice?

> Could we at least add a "ranges" property to the MC device description
> and check whether the physical addresses we get are within that range -
> if nothing else, at least as sanity check? Then maybe add some calls in
> the next version that act on that range rather than actual host physical
> addresses?

So you mean something like:

        fsl_mc: fsl-mc@80c000000 {
                compatible = "fsl,qoriq-mc";
                #stream-id-cells = <2>;
                reg = <0x00000008 0x0c000000 0 0x40>,    /* MC portal base */
                      <0x00000000 0x08340000 0 0x40000>; /* MC control reg */
                ranges = <0x8 0x0 0x8 0x0 0x20000000>;
                lpi-parent = <&its>;
        };

The physical addresses returned by the MC fall into a 512MB "portal"
region at 0x8_0000_0000 in the physical address map.  For now map it 1:1, but in the
future it could become:
                   ranges = <0x0 0x0 0x8 0x0 0x20000000>;

...if I can get the hardware architecture changed.

Stuart


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