[PATCH 0/2] mailbox: add support for clients to request channels by arguments

[PATCH 0/2] mailbox: add support for clients to request channels by arguments

[Tudor Ambarus]

There are clients that can discover channel identifiers at runtime by
parsing a shared memory for example, as in the ACPM interface's case.
For such cases passing the channel identifiers via DT is redundant.

Supply a new framework API: mbox_request_channel_by_args().

It works by supplying the usual client pointer as the first argument and
a pointer to a ``const struct mbox_xlate_args`` as a second. The newly
introduced struct is modeled after ``struct of_phandle_args``. The API
will search the client's node for a ``mbox`` phandle, identify the
controller's device node, and then call that controller's xlate() method
that will return a pointer to a mbox_chan or a ERR_PTR. The binding
between the channel and the client is done in the typical way.

This allows clients to reference the controller node as following:
        firmware {
                acpm_ipc: power-management {
                        compatible = "google,gs101-acpm-ipc";
-                       mboxes = <&ap2apm_mailbox 0 0
-                                 &ap2apm_mailbox 0 1
-                                 &ap2apm_mailbox 0 2
-                                 &ap2apm_mailbox 0 3
-                                 &ap2apm_mailbox 0 4
-                                 &ap2apm_mailbox 0 5
-                                 &ap2apm_mailbox 0 6
-                                 &ap2apm_mailbox 0 7
-                                 &ap2apm_mailbox 0 8
-                                 &ap2apm_mailbox 0 9
-                                 &ap2apm_mailbox 0 10
-                                 &ap2apm_mailbox 0 11
-                                 &ap2apm_mailbox 0 12
-                                 &ap2apm_mailbox 0 13
-                                 &ap2apm_mailbox 0 14>;
+                       mbox = <&ap2apm_mailbox>;
                        shmem = <&apm_sram>;
                };
        };

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
---
Tudor Ambarus (2):
      dt-bindings: mailbox: add support for referencing controllers solely by node
      mailbox: add support for clients to request channels by arguments

 .../devicetree/bindings/mailbox/mailbox.txt        | 19 ++++++--
 drivers/mailbox/mailbox.c                          | 57 ++++++++++++++++++++++
 include/linux/mailbox.h                            | 17 +++++++
 include/linux/mailbox_client.h                     |  3 ++
 include/linux/mailbox_controller.h                 |  4 ++
 5 files changed, 96 insertions(+), 4 deletions(-)
---
base-commit: 78d4f34e2115b517bcbfe7ec0d018bbbb6f9b0b8
change-id: 20241219-mbox_request_channel_by_args-7115089ed492

Best regards,
-- 
Tudor Ambarus <tudor.ambarus@linaro.org>

[PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Tudor Ambarus]

There are mailbox clients that can discover the mailbox channel ID at
run-time. For such cases passing the channel identifier via DT is
redundant. Add support for referencing controllers solely by node.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
---
 Documentation/devicetree/bindings/mailbox/mailbox.txt | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/mailbox/mailbox.txt b/Documentation/devicetree/bindings/mailbox/mailbox.txt
index af8ecee2ac68..0c4295a62f61 100644
--- a/Documentation/devicetree/bindings/mailbox/mailbox.txt
+++ b/Documentation/devicetree/bindings/mailbox/mailbox.txt
@@ -5,9 +5,10 @@ assign appropriate mailbox channel to client drivers.
 
 * Mailbox Controller
 
-Required property:
-- #mbox-cells: Must be at least 1. Number of cells in a mailbox
-		specifier.
+Optional property:
+- #mbox-cells: Must be at least 1. Number of cells in a mailbox specifier.
+               The property becomes mandatory for the cases where the clients
+               reference the controller via the mboxes property.
 
 Example:
 	mailbox: mailbox {
@@ -19,7 +20,11 @@ Example:
 * Mailbox Client
 
 Required property:
+Clients must reference the mailbox controller either via the mboxes or mbox
+properties.
 - mboxes: List of phandle and mailbox channel specifiers.
+- mbox: phandle pointing to the controller. Used by clients that can discover
+        the channel identifiers at runtime.
 
 Optional property:
 - mbox-names: List of identifier strings for each mailbox channel.
@@ -29,7 +34,13 @@ Optional property:
 	  communication between the mailbox client and the remote.
 
 
-Example:
+Example using mbox:
+	power-management {
+		...
+		mbox = <&mailbox>;
+	};
+
+Example using mboxes:
 	pwr_cntrl: power {
 		...
 		mbox-names = "pwr-ctrl", "rpc";

-- 
2.47.1.613.gc27f4b7a9f-goog

[PATCH 2/2] mailbox: add support for clients to request channels by arguments

[Tudor Ambarus]

There are clients that can discover channel identifiers at runtime by
parsing a shared memory for example, as in the ACPM interface's case.

Supply a new framework API: mbox_request_channel_by_args().

It works by supplying the usual client pointer as the first argument and
a pointer to a ``const struct mbox_xlate_args`` as a second. The newly
introduced struct is modeled after ``struct of_phandle_args``. The API
will search the client's node for a ``mbox`` phandle, identify the
controller's device node, and then call that controller's xlate() method
that will return a pointer to a mbox_chan or a ERR_PTR. The binding
between the channel and the client is done in the typical way.

Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
---
 drivers/mailbox/mailbox.c          | 57 ++++++++++++++++++++++++++++++++++++++
 include/linux/mailbox.h            | 17 ++++++++++++
 include/linux/mailbox_client.h     |  3 ++
 include/linux/mailbox_controller.h |  4 +++
 4 files changed, 81 insertions(+)

diff --git a/drivers/mailbox/mailbox.c b/drivers/mailbox/mailbox.c
index d3d26a2c9895..07ea32ebab80 100644
--- a/drivers/mailbox/mailbox.c
+++ b/drivers/mailbox/mailbox.c
@@ -467,6 +467,63 @@ struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 }
 EXPORT_SYMBOL_GPL(mbox_request_channel_byname);
 
+/**
+ * mbox_request_channel_by_args - request a mailbox channel using client's
+ * channel identifiers.
+ * @cl: identity of the client requesting the channel.
+ * @spec: arguments that describe the channel.
+ *
+ * Used by clients that can discover the channel identifiers at runtime (by
+ * parsing a shared memory for example). The description of
+ * mbox_request_channel() applies here as well.
+ *
+ * Return: Pointer to the channel assigned to the client if successful.
+ *         ERR_PTR for request failure.
+ */
+struct mbox_chan *mbox_request_channel_by_args(struct mbox_client *cl,
+					const struct mbox_xlate_args *spec)
+{
+	struct device *dev = cl->dev;
+	struct mbox_controller *mbox;
+	struct device_node *mbox_np;
+	struct mbox_chan *chan;
+	int ret;
+
+	if (!dev || !dev->of_node) {
+		pr_debug("%s: No owner device node\n", __func__);
+		return ERR_PTR(-ENODEV);
+	}
+
+	mbox_np = of_parse_phandle(dev_of_node(dev), "mbox", 0);
+	if (!mbox_np)
+		return ERR_PTR(-ENODEV);
+
+	mutex_lock(&con_mutex);
+
+	chan = ERR_PTR(-EPROBE_DEFER);
+	list_for_each_entry(mbox, &mbox_cons, node)
+		if (mbox->dev->of_node == mbox_np && mbox->xlate) {
+			chan = mbox->xlate(mbox, spec);
+			if (!IS_ERR(chan))
+				break;
+		}
+
+	of_node_put(mbox_np);
+
+	if (IS_ERR(chan)) {
+		mutex_unlock(&con_mutex);
+		return chan;
+	}
+
+	ret = __mbox_bind_client(chan, cl);
+	if (ret)
+		chan = ERR_PTR(ret);
+
+	mutex_unlock(&con_mutex);
+	return chan;
+}
+EXPORT_SYMBOL_GPL(mbox_request_channel_by_args);
+
 /**
  * mbox_free_channel - The client relinquishes control of a mailbox
  *			channel by this call.
diff --git a/include/linux/mailbox.h b/include/linux/mailbox.h
new file mode 100644
index 000000000000..cef88c5ae49d
--- /dev/null
+++ b/include/linux/mailbox.h
@@ -0,0 +1,17 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2024 Linaro Ltd.
+ */
+
+#ifndef __LINUX_MAILBOX_H
+#define __LINUX_MAILBOX_H
+
+#include <linux/types.h>
+
+#define MBOX_XLATE_MAX_ARGS 16
+struct mbox_xlate_args {
+	int args_count;
+	u32 args[MBOX_XLATE_MAX_ARGS];
+};
+
+#endif /* __LINUX_MAILBOX_H */
diff --git a/include/linux/mailbox_client.h b/include/linux/mailbox_client.h
index 734694912ef7..a9f4d108c48c 100644
--- a/include/linux/mailbox_client.h
+++ b/include/linux/mailbox_client.h
@@ -9,6 +9,7 @@
 
 #include <linux/of.h>
 #include <linux/device.h>
+#include <linux/mailbox.h>
 
 struct mbox_chan;
 
@@ -41,6 +42,8 @@ int mbox_bind_client(struct mbox_chan *chan, struct mbox_client *cl);
 struct mbox_chan *mbox_request_channel_byname(struct mbox_client *cl,
 					      const char *name);
 struct mbox_chan *mbox_request_channel(struct mbox_client *cl, int index);
+struct mbox_chan *mbox_request_channel_by_args(struct mbox_client *cl,
+			     const struct mbox_xlate_args *spec);
 int mbox_send_message(struct mbox_chan *chan, void *mssg);
 int mbox_flush(struct mbox_chan *chan, unsigned long timeout);
 void mbox_client_txdone(struct mbox_chan *chan, int r); /* atomic */
diff --git a/include/linux/mailbox_controller.h b/include/linux/mailbox_controller.h
index 6fee33cb52f5..dfddcf966f9f 100644
--- a/include/linux/mailbox_controller.h
+++ b/include/linux/mailbox_controller.h
@@ -8,6 +8,7 @@
 #include <linux/hrtimer.h>
 #include <linux/device.h>
 #include <linux/completion.h>
+#include <linux/mailbox.h>
 
 struct mbox_chan;
 
@@ -67,6 +68,7 @@ struct mbox_chan_ops {
  * @txpoll_period:	If 'txdone_poll' is in effect, the API polls for
  *			last TX's status after these many millisecs
  * @of_xlate:		Controller driver specific mapping of channel via DT
+ * @xlate:		Controller driver specific mapping of channel
  * @poll_hrt:		API private. hrtimer used to poll for TXDONE on all
  *			channels.
  * @node:		API private. To hook into list of controllers.
@@ -81,6 +83,8 @@ struct mbox_controller {
 	unsigned txpoll_period;
 	struct mbox_chan *(*of_xlate)(struct mbox_controller *mbox,
 				      const struct of_phandle_args *sp);
+	struct mbox_chan *(*xlate)(struct mbox_controller *mbox,
+				   const struct mbox_xlate_args *sp);
 	/* Internal to API */
 	struct hrtimer poll_hrt;
 	spinlock_t poll_hrt_lock;

-- 
2.47.1.613.gc27f4b7a9f-goog

Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Conor Dooley]

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On Thu, Dec 19, 2024 at 01:07:46PM +0000, Tudor Ambarus wrote:
> There are mailbox clients that can discover the mailbox channel ID at
> run-time. For such cases passing the channel identifier via DT is
> redundant. Add support for referencing controllers solely by node.

I don't really get your implementation, why not just allow #mbox-cells = 0?
That's what's done for things like fixed frequency clocks that only have
a single output.

Cheers,
Conor.

> 
> Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
> ---
>  Documentation/devicetree/bindings/mailbox/mailbox.txt | 19 +++++++++++++++----
>  1 file changed, 15 insertions(+), 4 deletions(-)
> 
> diff --git a/Documentation/devicetree/bindings/mailbox/mailbox.txt b/Documentation/devicetree/bindings/mailbox/mailbox.txt
> index af8ecee2ac68..0c4295a62f61 100644
> --- a/Documentation/devicetree/bindings/mailbox/mailbox.txt
> +++ b/Documentation/devicetree/bindings/mailbox/mailbox.txt
> @@ -5,9 +5,10 @@ assign appropriate mailbox channel to client drivers.
>  
>  * Mailbox Controller
>  
> -Required property:
> -- #mbox-cells: Must be at least 1. Number of cells in a mailbox
> -		specifier.
> +Optional property:
> +- #mbox-cells: Must be at least 1. Number of cells in a mailbox specifier.
> +               The property becomes mandatory for the cases where the clients
> +               reference the controller via the mboxes property.
>  
>  Example:
>  	mailbox: mailbox {
> @@ -19,7 +20,11 @@ Example:
>  * Mailbox Client
>  
>  Required property:
> +Clients must reference the mailbox controller either via the mboxes or mbox
> +properties.
>  - mboxes: List of phandle and mailbox channel specifiers.
> +- mbox: phandle pointing to the controller. Used by clients that can discover
> +        the channel identifiers at runtime.
>  
>  Optional property:
>  - mbox-names: List of identifier strings for each mailbox channel.
> @@ -29,7 +34,13 @@ Optional property:
>  	  communication between the mailbox client and the remote.
>  
>  
> -Example:
> +Example using mbox:
> +	power-management {
> +		...
> +		mbox = <&mailbox>;
> +	};
> +
> +Example using mboxes:
>  	pwr_cntrl: power {
>  		...
>  		mbox-names = "pwr-ctrl", "rpc";
> 
> -- 
> 2.47.1.613.gc27f4b7a9f-goog
> 

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Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Tudor Ambarus]

Hi, Conor,

On 12/19/24 2:11 PM, Conor Dooley wrote:
>> There are mailbox clients that can discover the mailbox channel ID at
>> run-time. For such cases passing the channel identifier via DT is
>> redundant. Add support for referencing controllers solely by node.
> I don't really get your implementation, why not just allow #mbox-cells = 0?
> That's what's done for things like fixed frequency clocks that only have
> a single output.

Ah, indeed!

instead of:
	of_parse_phandle(dev->of_node, "mbox", 0);
I can do a:
	of_parse_phandle_with_args(dev->of_node, "mboxes",
                                   "#mbox-cells", 0, &of_args)
where #mbox-cells = 0;

Or ... can I pass NULL for cells_name and make the #mbox-cells property
optional and still keeping its requirement of being at least 1?

Thanks!
ta

Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Conor Dooley]

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On Thu, Dec 19, 2024 at 03:42:11PM +0000, Tudor Ambarus wrote:
> Hi, Conor,
> 
> On 12/19/24 2:11 PM, Conor Dooley wrote:
> >> There are mailbox clients that can discover the mailbox channel ID at
> >> run-time. For such cases passing the channel identifier via DT is
> >> redundant. Add support for referencing controllers solely by node.
> > I don't really get your implementation, why not just allow #mbox-cells = 0?
> > That's what's done for things like fixed frequency clocks that only have
> > a single output.
> 
> Ah, indeed!
> 
> instead of:
> 	of_parse_phandle(dev->of_node, "mbox", 0);
> I can do a:
> 	of_parse_phandle_with_args(dev->of_node, "mboxes",
>                                    "#mbox-cells", 0, &of_args)
> where #mbox-cells = 0;
> 
> Or ... can I pass NULL for cells_name and make the #mbox-cells property
> optional and still keeping its requirement of being at least 1?

I think the mbox-cells = 0 approach is preferred, that property is what
marks it as a mailbox controller after all. Perhaps Rob or Krzysztof can
comment?

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Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Tudor Ambarus]

On 12/19/24 6:58 PM, Conor Dooley wrote:
> On Thu, Dec 19, 2024 at 03:42:11PM +0000, Tudor Ambarus wrote:
>> Hi, Conor,
>>
>> On 12/19/24 2:11 PM, Conor Dooley wrote:
>>>> There are mailbox clients that can discover the mailbox channel ID at
>>>> run-time. For such cases passing the channel identifier via DT is
>>>> redundant. Add support for referencing controllers solely by node.
>>> I don't really get your implementation, why not just allow #mbox-cells = 0?
>>> That's what's done for things like fixed frequency clocks that only have
>>> a single output.
>>
>> Ah, indeed!
>>
>> instead of:
>> 	of_parse_phandle(dev->of_node, "mbox", 0);
>> I can do a:
>> 	of_parse_phandle_with_args(dev->of_node, "mboxes",
>>                                    "#mbox-cells", 0, &of_args)
>> where #mbox-cells = 0;
>>
>> Or ... can I pass NULL for cells_name and make the #mbox-cells property
>> optional and still keeping its requirement of being at least 1?
> 
> I think the mbox-cells = 0 approach is preferred, that property is what
> marks it as a mailbox controller after all. Perhaps Rob or Krzysztof can
> comment?

I think using mbox-cells = 0 is better indeed. In my proposal I
considered the list to always have a single phandle, thus a reference to
a single mailbox controller, whereas it may be possible that clients to
reference multiple mailbox controllers. If so, #mbox-cells needs to be
defined in all the controllers, for consistency reasons, similar to what
happens with fixed clocks, as you already mentioned.

Thus I'll change the method to:
struct mbox_chan *mbox_request_channel_by_args(struct mbox_client *cl,
                       int index, const struct mbox_xlate_args *spec);
and use of_parse_phandle_with_args() in it.

Thanks, Conor!
ta

Re: [PATCH 1/2] dt-bindings: mailbox: add support for referencing controllers solely by node

[Conor Dooley]

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On Fri, Dec 20, 2024 at 07:51:32AM +0000, Tudor Ambarus wrote:
> 
> 
> On 12/19/24 6:58 PM, Conor Dooley wrote:
> > On Thu, Dec 19, 2024 at 03:42:11PM +0000, Tudor Ambarus wrote:
> >> Hi, Conor,
> >>
> >> On 12/19/24 2:11 PM, Conor Dooley wrote:
> >>>> There are mailbox clients that can discover the mailbox channel ID at
> >>>> run-time. For such cases passing the channel identifier via DT is
> >>>> redundant. Add support for referencing controllers solely by node.
> >>> I don't really get your implementation, why not just allow #mbox-cells = 0?
> >>> That's what's done for things like fixed frequency clocks that only have
> >>> a single output.
> >>
> >> Ah, indeed!
> >>
> >> instead of:
> >> 	of_parse_phandle(dev->of_node, "mbox", 0);
> >> I can do a:
> >> 	of_parse_phandle_with_args(dev->of_node, "mboxes",
> >>                                    "#mbox-cells", 0, &of_args)
> >> where #mbox-cells = 0;
> >>
> >> Or ... can I pass NULL for cells_name and make the #mbox-cells property
> >> optional and still keeping its requirement of being at least 1?
> > 
> > I think the mbox-cells = 0 approach is preferred, that property is what
> > marks it as a mailbox controller after all. Perhaps Rob or Krzysztof can
> > comment?
> 
> I think using mbox-cells = 0 is better indeed. In my proposal I
> considered the list to always have a single phandle, thus a reference to
> a single mailbox controller, whereas it may be possible that clients to
> reference multiple mailbox controllers. If so, #mbox-cells needs to be
> defined in all the controllers, for consistency reasons, similar to what
> happens with fixed clocks, as you already mentioned.

Oh right, I had totally forgotten about that, that's a solid argument
for the mbox-cells = 0 approach for sure.

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