Date:	Wed, 22 Jun 2011 10:55:24 -0700
From:	Randy Dunlap <rdunlap@...otime.net>
To:	Ohad Ben-Cohen <ohad@...ery.com>
Cc:	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<linux-arm-kernel@...ts.infradead.org>,
	<akpm@...ux-foundation.org>, Brian Swetland <swetland@...gle.com>,
	Arnd Bergmann <arnd@...db.de>,
	Grant Likely <grant.likely@...retlab.ca>,
	davinci-linux-open-source 
	<davinci-linux-open-source@...ux.davincidsp.com>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [RFC 1/8] drivers: add generic remoteproc framework

On Tue, 21 Jun 2011 10:18:27 +0300 Ohad Ben-Cohen wrote:

Hi,
Just a few minor nits inline...


> diff --git a/Documentation/remoteproc.txt b/Documentation/remoteproc.txt
> new file mode 100644
> index 0000000..3075813
> --- /dev/null
> +++ b/Documentation/remoteproc.txt
> @@ -0,0 +1,170 @@
> +Remote Processor Framework
> +
> +1. Introduction
> +
> +Modern SoCs typically have heterogeneous remote processor devices in asymmetric
> +multiprocessing (AMP) configurations, which may be running different instances
> +of operating system, whether it's Linux or any other flavor of real-time OS.
> +
> +OMAP4, for example, has dual Cortex-A9, dual Cortex-M3 and a C64x+ DSP.
> +In a typical configuration, the dual cortex-A9 is running Linux in a SMP
> +configuration, and each of the other three cores (two M3 cores and a DSP)
> +is running its own instance of RTOS in an AMP configuration.
> +
> +The generic remoteproc driver allows different platforms/architectures to
> +control (power on, load firmware, power off) those remote processors while
> +abstracting the hardware differences, so the entire driver doesn't need to be
> +duplicated.
> +
> +2. User API
> +
> +  struct rproc *rproc_get(const char *name);
> +   - power up the remote processor, identified by the 'name' argument,
> +     and boot it. If the remote processor is already powered on, the
> +     function immediately succeeds.
> +     On success, returns the rproc handle. On failure, NULL is returned.
> +
> +  void rproc_put(struct rproc *rproc);
> +   - power off the remote processor, identified by the rproc handle.
> +     Every call to rproc_get() must be (eventually) accompanied by a call
> +     to rproc_put(). Calling rproc_put() redundantly is a bug.
> +     Note: the remote processor will actually be powered off only when the
> +     last user calls rproc_put().
> +
> +3. Typical usage
> +
> +#include <linux/remoteproc.h>
> +
> +int dummy_rproc_example(void)
> +{
> +	struct rproc *my_rproc;
> +
> +	/* let's power on and boot the image processing unit */
> +	my_rproc = rproc_get("ipu");
> +	if (!my_rproc) {
> +		/*
> +		 * something went wrong. handle it and leave.
> +		 */
> +	}
> +
> +	/*
> +	 * the 'ipu' remote processor is now powered on... let it work !
> +	 */
> +
> +	/* if we no longer need ipu's services, power it down */
> +	rproc_put(my_rproc);
> +}
> +
> +4. API for implementors
> +
> +  int rproc_register(struct device *dev, const char *name,
> +				const struct rproc_ops *ops,
> +				const char *firmware,
> +				const struct rproc_mem_entry *memory_maps,
> +				struct module *owner);
> +   - should be called from the underlying platform-specific implementation, in
> +     order to register a new remoteproc device. 'dev' is the underlying
> +     device, 'name' is the name of the remote processor, which will be
> +     specified by users calling rproc_get(), 'ops' is the platform-specific
> +     start/stop handlers, 'firmware' is the name of the firmware file to
> +     boot the processor with, 'memory_maps' is a table of da<->pa memory
> +     mappings which should be used to configure the IOMMU (if not relevant,
> +     just pass NULL here), 'owner' is the underlying module that should
> +     not be removed while the remote processor is in use.
> +
> +     Returns 0 on success, or an appropriate error code on failure.
> +
> +  int rproc_unregister(const char *name);
> +   - should be called from the underlying platform-specific implementation, in
> +     order to unregister a remoteproc device that was previously registered
> +     with rproc_register().
> +
> +5. Implementation callbacks
> +
> +Every remoteproc implementation must provide these handlers:
> +
> +struct rproc_ops {
> +	int (*start)(struct rproc *rproc, u64 bootaddr);
> +	int (*stop)(struct rproc *rproc);
> +};
> +
> +The ->start() handler takes a rproc handle and an optional bootaddr argument,

                               an rproc

> +and should power on the device and boot it (using the bootaddr argument
> +if the hardware requires one).
> +On success, 0 is returned, and on failure, an appropriate error code.
> +
> +The ->stop() handler takes a rproc handle and powers the device off.

                              an rproc

> +On success, 0 is returned, and on failure, an appropriate error code.
> +
> +6. Binary Firmware Structure
> +
> +The following enums and structures define the binary format of the images
> +remoteproc loads and boot the remote processors with.

                        boots

> +
> +The general binary format is as follows:
> +
> +struct {
> +      char magic[4] = { 'R', 'P', 'R', 'C' };
> +      u32 version;
> +      u32 header_len;
> +      char header[...] = { header_len bytes of unformatted, textual header };
> +      struct section {
> +          u32 type;
> +          u64 da;
> +          u32 len;
> +          u8 content[...] = { len bytes of binary data };
> +      } [ no limit on number of sections ];
> +} __packed;
> +
> +The image begins with a 4-bytes "RPRC" magic, a version number, and a
> +free-style textual header that users can easily read.
> +
> +After the header, the firmware contains several sections that should be
> +loaded to memory so the remote processor can access them.
> +
> +Every section begins with its type, device address (da) where the remote
> +processor expects to find this section at (exact meaning depends whether

                            drop:         at

> +the device accesses memory through an IOMMU or not. if not, da might just
> +be physical addresses), the section length and its content.
> +
> +Most of the sections are either text or data (which currently are treated
> +exactly the same), but there is one special "resource" section that allows
> +the remote processor to announce/request certain resources from the host.
> +
> +A resource section is just a packed array of the following struct:
> +
> +struct fw_resource {
> +	u32 type;
> +	u64 da;
> +	u64 pa;
> +	u32 len;
> +	u32 flags;
> +	u8 name[48];
> +} __packed;
> +
> +The way a resource is really handled strongly depends on its type.
> +Some resources are just one-way announcements, e.g., a RSC_TRACE type means
> +that the remote processor will be writing log messages into a trace buffer
> +which is located at the address specified in 'da'. In that case, 'len' is
> +the size of that buffer. A RSC_BOOTADDR resource type announces the boot
> +address (i.e. the first instruction the remote processor should be booted with)
> +in 'da'.
> +
> +Other resources entries might be a two-way request/respond negotiation where
> +a certain resource (memory or any other hardware resource) is requested
> +by specifying the appropriate type and name. The host should then allocate
> +such a resource and "reply" by writing the identifier (physical address
> +or any other device id that will be meaningful to the remote processor)
> +back into the relevant member of the resource structure. Obviously this
> +approach can only be used _before_ booting the remote processor. After
> +the remote processor is powered up, the resource section is expected
> +to stay static. Runtime resource management (i.e. handling requests after
> +the remote processor has booted) will be achieved using a dedicated rpmsg
> +driver.
> +
> +The latter two-way approach is still preliminary and has not been implemented
> +yet. It's left to see how this all works out.
> +
> +Most likely this kind of static allocations of hardware resources for
> +remote processors can also use DT, so it's interesting to see how
> +this all work out when DT materializes.

            works out


thanks,
---
~Randy
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