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From:   Ben Levinsky <ben.levinsky@xilinx.com>
To:     <mathieu.poirier@linaro.org>, <arnaud.pouliquen@foss.st.com>,
        <bill.mills@linaro.com>, <tanmay.shah@amd.com>
CC:     <linux-remoteproc@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: [RFC PATCH 0/1] remoteproc: Enable getter for drivers that manage 2+ remotes
Date:   Tue, 15 Nov 2022 07:37:52 -0800
Message-ID: <20221115153753.2065803-1-ben.levinsky@xilinx.com>
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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