linux-kernel - Re: [PATCH 1/3 v4] drivers/bus: Added Freescale Management Complex APIs

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Date:	Thu, 27 Nov 2014 17:14:01 +0100
From:	Alexander Graf <agraf@...e.de>
To:	"J. German Rivera" <German.Rivera@...escale.com>,
	gregkh@...uxfoundation.org, arnd@...db.de,
	linux-kernel@...r.kernel.org
CC:	stuart.yoder@...escale.com, Kim.Phillips@...escale.com,
	scottwood@...escale.com, bhamciu1@...escale.com,
	R89243@...escale.com, Geoff.Thorpe@...escale.com,
	bhupesh.sharma@...escale.com, nir.erez@...escale.com,
	richard.schmitt@...escale.com
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@...escale.com>
> Signed-off-by: Stuart Yoder <stuart.yoder@...escale.com>

[...]

> +/**
> + * 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.

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.

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?


Alex
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