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Message-ID: <2a25af37-a9b8-e4f3-6092-06c1c907dc9f@gmail.com>
Date: Tue, 23 Jun 2020 17:21:44 -0500
From: Frank Rowand <frowand.list@...il.com>
To: Lee Jones <lee.jones@...aro.org>, andy.shevchenko@...il.com,
michael@...le.cc, robh+dt@...nel.org, broonie@...nel.org,
devicetree@...r.kernel.org, linus.walleij@...aro.org,
linux@...ck-us.net, andriy.shevchenko@...ux.intel.com,
robin.murphy@....com, gregkh@...uxfoundation.org
Cc: linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
Frank Rowand <frowand.list@...il.com>
Subject: Re: [PATCH v2 1/3] mfd: core: Make a best effort attempt to match
devices with the correct of_nodes
On 2020-06-11 14:10, Lee Jones wrote:
> Currently, when a child platform device (sometimes referred to as a
> sub-device) is registered via the Multi-Functional Device (MFD) API,
> the framework attempts to match the newly registered platform device
> with its associated Device Tree (OF) node. Until now, the device has
> been allocated the first node found with an identical OF compatible
> string. Unfortunately, if there are, say for example '3' devices
> which are to be handled by the same driver and therefore have the same
> compatible string, each of them will be allocated a pointer to the
> *first* node.
>
> An example Device Tree entry might look like this:
>
> mfd_of_test {
> compatible = "mfd,of-test-parent";
> #address-cells = <0x02>;
> #size-cells = <0x02>;
>
> child@...aaaaaaaaaaaaa {
> compatible = "mfd,of-test-child";
> reg = <0xaaaaaaaa 0xaaaaaaaa 0 0x11>,
> <0xbbbbbbbb 0xbbbbbbbb 0 0x22>;
> };
>
> child@...ccccc {
> compatible = "mfd,of-test-child";
> reg = <0x00000000 0xcccccccc 0 0x33>;
> };
>
> child@...ddddd00000000 {
> compatible = "mfd,of-test-child";
> reg = <0xdddddddd 0x00000000 0 0x44>;
> };
> };
>
> When used with example sub-device registration like this:
>
> static const struct mfd_cell mfd_of_test_cell[] = {
> OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 0, "mfd,of-test-child"),
> OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"),
> OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child")
> };
>
> ... the current implementation will result in all devices being allocated
> the first OF node found containing a matching compatible string:
>
> [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
> [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@...aaaaaaaaaaaaa
> [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
> [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@...aaaaaaaaaaaaa
> [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
> [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@...aaaaaaaaaaaaa
>
> After this patch each device will be allocated a unique OF node:
>
> [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
> [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@...aaaaaaaaaaaaa
> [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
> [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@...ccccc
> [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
> [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@...ddddd00000000
>
> Which is fine if all OF nodes are identical. However if we wish to
> apply an attribute to particular device, we really need to ensure the
> correct OF node will be associated with the device containing the
> correct address. We accomplish this by matching the device's address
> expressed in DT with one provided during sub-device registration.
> Like this:
>
> static const struct mfd_cell mfd_of_test_cell[] = {
> OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child", 0xdddddddd00000000),
> OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa),
> OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc)
> };
>
> This will ensure a specific device (designated here using the
> platform_ids; 1, 2 and 3) is matched with a particular OF node:
>
> [0.712511] mfd-of-test-child mfd-of-test-child.0: Probing platform device: 0
> [0.712710] mfd-of-test-child mfd-of-test-child.0: Using OF node: child@...ddddd00000000
> [0.713033] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
> [0.713381] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@...aaaaaaaaaaaaa
> [0.713691] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
> [0.713889] mfd-of-test-child mfd-of-test-child.2: Using OF node: child@...ccccc
>
> This implementation is still not infallible, hence the mention of
> "best effort" in the commit subject. Since we have not *insisted* on
> the existence of 'reg' properties (in some scenarios they just do not
> make sense) and no device currently uses the new 'of_reg' attribute,
> we have to make an on-the-fly judgement call whether to associate the
> OF node anyway. Which we do in cases where parent drivers haven't
> specified a particular OF node to match to. So there is a *slight*
> possibility of the following result (note: the implementation here is
> convoluted, but it shows you one means by which this process can
> still break):
>
> /*
> * First entry will match to the first OF node with matching compatible
> * Second will fail, since the first took its OF node and is no longer available
> * Third will succeed
> */
> static const struct mfd_cell mfd_of_test_cell[] = {
> OF_MFD_CELL("mfd-of-test-child", NULL, NULL, 0, 1, "mfd,of-test-child"),
> OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 2, "mfd,of-test-child", 0xaaaaaaaaaaaaaaaa),
> OF_MFD_CELL_REG("mfd-of-test-child", NULL, NULL, 0, 3, "mfd,of-test-child", 0x00000000cccccccc)
> };
>
> The result:
>
> [0.753869] mfd-of-test-parent mfd_of_test: Registering 3 devices
> [0.756597] mfd-of-test-child: Failed to locate of_node [id: 2]
> [0.759999] mfd-of-test-child mfd-of-test-child.1: Probing platform device: 1
> [0.760314] mfd-of-test-child mfd-of-test-child.1: Using OF node: child@...aaaaaaaaaaaaa
> [0.760908] mfd-of-test-child mfd-of-test-child.2: Probing platform device: 2
> [0.761183] mfd-of-test-child mfd-of-test-child.2: No OF node associated with this device
> [0.761621] mfd-of-test-child mfd-of-test-child.3: Probing platform device: 3
> [0.761899] mfd-of-test-child mfd-of-test-child.3: Using OF node: child@...ccccc
>
> We could code around this with some pre-parsing semantics, but the
> added complexity required to cover each and every corner-case is not
> justified. Merely patching the current failing (via this patch) is
> already working with some pretty small corner-cases. Other issues
> should be patched in the parent drivers which can be achieved simply
> by implementing OF_MFD_CELL_REG().
>
> Signed-off-by: Lee Jones <lee.jones@...aro.org>
> ---
>
> Changelog:
>
> v1 => v2:
> * Simply return -EAGAIN if node is already in use
> * Allow for valid of_reg=0 by introducing use_of_reg boolean flag
> * Split helpers out into separate patch
>
> drivers/mfd/mfd-core.c | 99 +++++++++++++++++++++++++++++++++++-----
> include/linux/mfd/core.h | 10 ++++
> 2 files changed, 97 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/mfd/mfd-core.c b/drivers/mfd/mfd-core.c
> index e831e733b38cf..120803717b828 100644
> --- a/drivers/mfd/mfd-core.c
> +++ b/drivers/mfd/mfd-core.c
> @@ -10,6 +10,7 @@
> #include <linux/kernel.h>
> #include <linux/platform_device.h>
> #include <linux/acpi.h>
> +#include <linux/list.h>
> #include <linux/property.h>
> #include <linux/mfd/core.h>
> #include <linux/pm_runtime.h>
> @@ -17,8 +18,17 @@
> #include <linux/module.h>
> #include <linux/irqdomain.h>
> #include <linux/of.h>
> +#include <linux/of_address.h>
> #include <linux/regulator/consumer.h>
>
> +static LIST_HEAD(mfd_of_node_list);
> +
> +struct mfd_of_node_entry {
> + struct list_head list;
> + struct device *dev;
> + struct device_node *np;
> +};
> +
> static struct device_type mfd_dev_type = {
> .name = "mfd_device",
> };
> @@ -107,6 +117,54 @@ static inline void mfd_acpi_add_device(const struct mfd_cell *cell,
> }
> #endif
>
> +static int mfd_match_of_node_to_dev(struct platform_device *pdev,
> + struct device_node *np,
> + const struct mfd_cell *cell)
> +{
> + struct mfd_of_node_entry *of_entry;
> + const __be32 *reg;
> + u64 of_node_addr;
> +
> + /* Skip devices 'disabled' by Device Tree */
> + if (!of_device_is_available(np))
> + return -ENODEV;
> +
> + /* Skip if OF node has previously been allocated to a device */
> + list_for_each_entry(of_entry, &mfd_of_node_list, list)
> + if (of_entry->np == np)
> + return -EAGAIN;
> +
> + if (!cell->use_of_reg)
> + /* No of_reg defined - allocate first free compatible match */
> + goto allocate_of_node;
> +
> + /* We only care about each node's first defined address */
> + reg = of_get_address(np, 0, NULL, NULL);
> + if (!reg)
> + /* OF node does not contatin a 'reg' property to match to */
> + return -EAGAIN;
> +
> + of_node_addr = of_read_number(reg, of_n_addr_cells(np));
> +
> + if (cell->of_reg != of_node_addr)
> + /* No match */
> + return -EAGAIN;
> +
> +allocate_of_node:
> + of_entry = kzalloc(sizeof(*of_entry), GFP_KERNEL);
> + if (!of_entry)
> + return -ENOMEM;
> +
> + of_entry->dev = &pdev->dev;
> + of_entry->np = np;
> + list_add_tail(&of_entry->list, &mfd_of_node_list);
> +
> + pdev->dev.of_node = np;
> + pdev->dev.fwnode = &np->fwnode;
> +
> + return 0;
> +}
> +
> static int mfd_add_device(struct device *parent, int id,
> const struct mfd_cell *cell,
> struct resource *mem_base,
> @@ -115,6 +173,7 @@ static int mfd_add_device(struct device *parent, int id,
> struct resource *res;
> struct platform_device *pdev;
> struct device_node *np = NULL;
> + struct mfd_of_node_entry *of_entry, *tmp;
> int ret = -ENOMEM;
> int platform_id;
> int r;
> @@ -149,19 +208,22 @@ static int mfd_add_device(struct device *parent, int id,
> if (ret < 0)
> goto fail_res;
>
> - if (parent->of_node && cell->of_compatible) {
> + if (IS_ENABLED(CONFIG_OF) && parent->of_node && cell->of_compatible) {
> for_each_child_of_node(parent->of_node, np) {
> if (of_device_is_compatible(np, cell->of_compatible)) {
> - if (!of_device_is_available(np)) {
> - /* Ignore disabled devices error free */
> - ret = 0;
> + ret = mfd_match_of_node_to_dev(pdev, np, cell);
> + if (ret == -EAGAIN)
> + continue;
> + if (ret)
> goto fail_alias;
> - }
> - pdev->dev.of_node = np;
> - pdev->dev.fwnode = &np->fwnode;
> +
> break;
> }
> }
> +
> + if (!pdev->dev.of_node)
> + pr_warn("%s: Failed to locate of_node [id: %d]\n",
> + cell->name, platform_id);
> }
>
> mfd_acpi_add_device(cell, pdev);
> @@ -170,13 +232,13 @@ static int mfd_add_device(struct device *parent, int id,
> ret = platform_device_add_data(pdev,
> cell->platform_data, cell->pdata_size);
> if (ret)
> - goto fail_alias;
> + goto fail_of_entry;
> }
>
> if (cell->properties) {
> ret = platform_device_add_properties(pdev, cell->properties);
> if (ret)
> - goto fail_alias;
> + goto fail_of_entry;
> }
>
> for (r = 0; r < cell->num_resources; r++) {
> @@ -213,18 +275,18 @@ static int mfd_add_device(struct device *parent, int id,
> if (has_acpi_companion(&pdev->dev)) {
> ret = acpi_check_resource_conflict(&res[r]);
> if (ret)
> - goto fail_alias;
> + goto fail_of_entry;
> }
> }
> }
>
> ret = platform_device_add_resources(pdev, res, cell->num_resources);
> if (ret)
> - goto fail_alias;
> + goto fail_of_entry;
>
> ret = platform_device_add(pdev);
> if (ret)
> - goto fail_alias;
> + goto fail_of_entry;
>
> if (cell->pm_runtime_no_callbacks)
> pm_runtime_no_callbacks(&pdev->dev);
> @@ -233,6 +295,12 @@ static int mfd_add_device(struct device *parent, int id,
>
> return 0;
>
> +fail_of_entry:
> + list_for_each_entry_safe(of_entry, tmp, &mfd_of_node_list, list)
> + if (of_entry->dev == &pdev->dev) {
> + list_del(&of_entry->list);
> + kfree(of_entry);
> + }
> fail_alias:
> regulator_bulk_unregister_supply_alias(&pdev->dev,
> cell->parent_supplies,
> @@ -287,6 +355,7 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
> {
> struct platform_device *pdev;
> const struct mfd_cell *cell;
> + struct mfd_of_node_entry *of_entry, *tmp;
>
> if (dev->type != &mfd_dev_type)
> return 0;
> @@ -297,6 +366,12 @@ static int mfd_remove_devices_fn(struct device *dev, void *data)
> regulator_bulk_unregister_supply_alias(dev, cell->parent_supplies,
> cell->num_parent_supplies);
>
> + list_for_each_entry_safe(of_entry, tmp, &mfd_of_node_list, list)
> + if (of_entry->dev == dev) {
> + list_del(&of_entry->list);
> + kfree(of_entry);
> + }
> +
> kfree(cell);
>
> platform_device_unregister(pdev);
> diff --git a/include/linux/mfd/core.h b/include/linux/mfd/core.h
> index d01d1299e49dc..a148b907bb7f1 100644
> --- a/include/linux/mfd/core.h
> +++ b/include/linux/mfd/core.h
> @@ -78,6 +78,16 @@ struct mfd_cell {
> */
> const char *of_compatible;
>
> + /*
> + * Address as defined in Device Tree. Used to compement 'of_compatible'
> + * (above) when matching OF nodes with devices that have identical
> + * compatible strings
> + */
Instead of the above comment, suggest something like instead (I have not properly
line wrapped, to make it easier to see the difference):
> + /*
> + * Address as defined in Device Tree mfd child node "reg" property. Used in combination with 'of_compatible'
> + * (above) when matching OF nodes with devices that have identical
> + * compatible strings
> + */
> + const u64 of_reg;
> +
> + /* Set to 'true' to use 'of_reg' (above) - allows for of_reg=0 */
> + bool use_of_reg;
> +
> /* Matches ACPI */
> const struct mfd_cell_acpi_match *acpi_match;
>
>
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