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Subject[RFC PATCH 0/1] remoteproc: Enable getter for drivers that manage 2+ remotes
Date
This RFC is to show the following
(a) a use case for a new remoteproc API rproc_get_by_id()
(b) patch for the new API rproc_get_by_id()

For context there exist multiple drivers in remoteproc that manage more than
one remote processor. For these drivers, calls to rproc_get_by_phandle()
are not sufficient as the check at
https://github.com/torvalds/linux/blob/master/drivers/remoteproc/remoteproc_core.c#L2111
will not work. This is because for r->dev.parent, r->dev's parent is
expected to be the platform device that corresponds to the platform-probe()
call but instead is the child and this child does not have the driver field
set.

An example to show this issue is as follows:

If a remoteproc driver has the following DTS binding:

/{
remoteproc_cluster {
compatible = "soc,remoteproc-cluster";

core0: core0 {
memory-region;
sram;
};

core1: core1 {
memory-region;
sram;
}
};
};

And in the corresponding driver the platform-probe() is as follows:

static int cluster_platform_probe(struct platform_device *pdev)
{
struct device_node *np = dev_of_node(dev);
struct device *dev = &pdev->dev;
struct platform_device *cpdev;
struct device *child_dev;
struct rproc *rp;

for_each_available_child_of_node(np, child) {
cpdev = of_find_device_by_node(child);
child_dev = &cpdev->dev;

rp = rproc_alloc(cdev, dev_name(cdev), dummy_ops, NULL,
sizeof(struct dummy_ops));
}

return 0;
}


After the rproc call is done and when another driver tries to access this
rproc structure via a rproc_get_by_phandle(), the aforementioned check of
r->dev.parent->driver will be NULL.

To account for a remoteproc driver that manages multiple remote processors,
I have provided an API rproc_get_by_id() that enables getting rp
given a phandle to the core in question with a DT binding and usage of the API.

Sample binding:

/{
platform_driver_sample {
compatible = "custom_platform";
rproc = <&core1>;
};
};

Sample usage:

static int custom_platform_probe(struct platform_device *pdev)
{
struct rproc *rp;
struct device_node *node;

node = of_parse_phandle(pdev->dev.of_node, "rproc", 0);

/* Here get rproc 1, as its index should be 1 */
rp = rproc_get_by_id(node->phandle, 1);

return 0;
}

If we want further specification of getting the correct remoteproc ID,
this can be inferred from the pdev->dev child's device child node and
its dev->init_name field as this is set in rproc_alloc() as follows:

dev_set_name(&rproc->dev, "remoteproc%d", rproc->index);

We can then parse the pdev->dev child device as follows:

int index;

sscanf(dev_name(dev), "remoteproc%d", &index);

Additionally I have provided the implementation for the API in
the subsequent patch.

Ben Levinsky (1):
remoteproc: Introduce rproc_get_by_id API

drivers/remoteproc/remoteproc_core.c | 64 +++++++++++++++++++++++++++-
include/linux/remoteproc.h | 1 +
2 files changed, 64 insertions(+), 1 deletion(-)

--
2.25.1

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