[PATCH V7 0/2] mailbox: arm: introduce smc triggered mailbox

[PATCH V7 0/2] mailbox: arm: introduce smc triggered mailbox

[Peng Fan]

From: Peng Fan <peng.fan@nxp.com>

V7:
Typo fix
#mbox-cells changed to 0
Add a new header file arm-smccc-mbox.h
Use ARM_SMCCC_IS_64

Andre,
  The function_id is still kept in arm_smccc_mbox_cmd, because arm,func-id
property is optional, so clients could pass function_id to mbox driver.

V6:
Switch to per-channel a mbox controller
Drop arm,num-chans, transports, method
Add arm,hvc-mbox compatible
Fix smc/hvc args, drop client id and use correct type.
https://patchwork.kernel.org/cover/11146641/

V5:
yaml fix
https://patchwork.kernel.org/cover/11117741/

V4:
yaml fix for num-chans in patch 1/2.
https://patchwork.kernel.org/cover/11116521/

V3:
Drop interrupt
Introduce transports for mem/reg usage
Add chan-id for mem usage
Convert to yaml format
https://patchwork.kernel.org/cover/11043541/
 
V2:
This is a modified version from Andre Przywara's patch series
https://lore.kernel.org/patchwork/cover/812997/.
The modification are mostly:
Introduce arm,num-chans
Introduce arm_smccc_mbox_cmd
txdone_poll and txdone_irq are both set to false
arm,func-ids are kept, but as an optional property.
Rewords SCPI to SCMI, because I am trying SCMI over SMC, not SCPI.
Introduce interrupts notification.

[1] is a draft implementation of i.MX8MM SCMI ATF implementation that
use smc as mailbox, power/clk is included, but only part of clk has been
implemented to work with hardware, power domain only supports get name
for now.

The traditional Linux mailbox mechanism uses some kind of dedicated hardware
IP to signal a condition to some other processing unit, typically a dedicated
management processor.
This mailbox feature is used for instance by the SCMI protocol to signal a
request for some action to be taken by the management processor.
However some SoCs does not have a dedicated management core to provide
those services. In order to service TEE and to avoid linux shutdown
power and clock that used by TEE, need let firmware to handle power
and clock, the firmware here is ARM Trusted Firmware that could also
run SCMI service.

The existing SCMI implementation uses a rather flexible shared memory
region to communicate commands and their parameters, it still requires a
mailbox to actually trigger the action.

This patch series provides a Linux mailbox compatible service which uses
smc calls to invoke firmware code, for instance taking care of SCMI requests.
The actual requests are still communicated using the standard SCMI way of
shared memory regions, but a dedicated mailbox hardware IP can be replaced via
this new driver.

This simple driver uses the architected SMC calling convention to trigger
firmware services, also allows for using "HVC" calls to call into hypervisors
or firmware layers running in the EL2 exception level.

Patch 1 contains the device tree binding documentation, patch 2 introduces
the actual mailbox driver.

Please note that this driver just provides a generic mailbox mechanism,
It could support synchronous TX/RX, or synchronous TX with asynchronous
RX. And while providing SCMI services was the reason for this exercise,
this driver is in no way bound to this use case, but can be used generically
where the OS wants to signal a mailbox condition to firmware or a
hypervisor.
Also the driver is in no way meant to replace any existing firmware
interface, but actually to complement existing interfaces.

[1] https://github.com/MrVan/arm-trusted-firmware/tree/scmi



Peng Fan (2):
  dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox
  mailbox: introduce ARM SMC based mailbox

 .../devicetree/bindings/mailbox/arm-smc.yaml       |  95 ++++++++++++
 drivers/mailbox/Kconfig                            |   7 +
 drivers/mailbox/Makefile                           |   2 +
 drivers/mailbox/arm-smc-mailbox.c                  | 168 +++++++++++++++++++++
 4 files changed, 272 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.yaml
 create mode 100644 drivers/mailbox/arm-smc-mailbox.c

-- 
2.16.4


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[PATCH V7 1/2] dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox

[Peng Fan]

From: Peng Fan <peng.fan@nxp.com>

The ARM SMC/HVC mailbox binding describes a firmware interface to trigger
actions in software layers running in the EL2 or EL3 exception levels.
The term "ARM" here relates to the SMC instruction as part of the ARM
instruction set, not as a standard endorsed by ARM Ltd.

Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 .../devicetree/bindings/mailbox/arm-smc.yaml       | 95 ++++++++++++++++++++++
 1 file changed, 95 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.yaml

diff --git a/Documentation/devicetree/bindings/mailbox/arm-smc.yaml b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml
new file mode 100644
index 000000000000..8764ad2726b2
--- /dev/null
+++ b/Documentation/devicetree/bindings/mailbox/arm-smc.yaml
@@ -0,0 +1,95 @@
+# SPDX-License-Identifier: (GPL-2.0 OR BSD-2-Clause)
+%YAML 1.2
+---
+$id: http://devicetree.org/schemas/mailbox/arm-smc.yaml#
+$schema: http://devicetree.org/meta-schemas/core.yaml#
+
+title: ARM SMC Mailbox Interface
+
+maintainers:
+  - Peng Fan <peng.fan@nxp.com>
+
+description: |
+  This mailbox uses the ARM smc (secure monitor call) or hvc (hypervisor
+  call) instruction to trigger a mailbox-connected activity in firmware,
+  executing on the very same core as the caller. The value of r0/w0/x0
+  the firmware returns after the smc call is delivered as a received
+  message to the mailbox framework, so synchronous communication can be
+  established. The exact meaning of the action the mailbox triggers as
+  well as the return value is defined by their users and is not subject
+  to this binding.
+
+  One example use case of this mailbox is the SCMI interface, which uses
+  shared memory to transfer commands and parameters, and a mailbox to
+  trigger a function call. This allows SoCs without a separate management
+  processor (or when such a processor is not available or used) to use
+  this standardized interface anyway.
+
+  This binding describes no hardware, but establishes a firmware interface.
+  Upon receiving an SMC using the described SMC function identifier, the
+  firmware is expected to trigger some mailbox connected functionality.
+  The communication follows the ARM SMC calling convention.
+  Firmware expects an SMC function identifier in r0 or w0. The supported
+  identifier are passed from consumers, or listed in the the arm,func-id
+  property as described below. The firmware can return one value in
+  the first SMC result register, it is expected to be an error value,
+  which shall be propagated to the mailbox client.
+
+  Any core which supports the SMC or HVC instruction can be used, as long
+  as a firmware component running in EL3 or EL2 is handling these calls.
+
+properties:
+  compatible:
+    oneOf:
+      - description:
+          For implementations using ARM SMC instruction.
+        const: arm,smc-mbox
+
+      - description:
+          For implementations using ARM HVC instruction.
+        const: arm,hvc-mbox
+
+  "#mbox-cells":
+    const: 0
+
+  arm,func-id:
+    description: |
+      An single 32-bit value specifying the function ID used by the mailbox.
+      The function ID follows the ARM SMC calling convention standard.
+    $ref: /schemas/types.yaml#/definitions/uint32
+
+required:
+  - compatible
+  - "#mbox-cells"
+
+examples:
+  - |
+    sram@93f000 {
+      compatible = "mmio-sram";
+      reg = <0x0 0x93f000 0x0 0x1000>;
+      #address-cells = <1>;
+      #size-cells = <1>;
+      ranges = <0x0 0x93f000 0x1000>;
+
+      cpu_scp_lpri: scp-shmem@0 {
+        compatible = "arm,scmi-shmem";
+        reg = <0x0 0x200>;
+      };
+    };
+
+    smc_tx_mbox: tx_mbox {
+      #mbox-cells = <0>;
+      compatible = "arm,smc-mbox";
+      arm,func-id = <0xc20000fe>;
+    };
+
+    firmware {
+      scmi {
+        compatible = "arm,scmi";
+        mboxes = <&smc_tx_mbox>;
+        mbox-names = "tx";
+        shmem = <&cpu_scp_lpri>;
+      };
+    };
+
+...
-- 
2.16.4


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[PATCH V7 2/2] mailbox: introduce ARM SMC based mailbox

[Peng Fan]

From: Peng Fan <peng.fan@nxp.com>

This mailbox driver implements a mailbox which signals transmitted data
via an ARM smc (secure monitor call) instruction. The mailbox receiver
is implemented in firmware and can synchronously return data when it
returns execution to the non-secure world again.
An asynchronous receive path is not implemented.
This allows the usage of a mailbox to trigger firmware actions on SoCs
which either don't have a separate management processor or on which such
a core is not available. A user of this mailbox could be the SCP
interface.

Modified from Andre Przywara's v2 patch
https://lore.kernel.org/patchwork/patch/812999/

Cc: Andre Przywara <andre.przywara@arm.com>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
---
 drivers/mailbox/Kconfig           |   7 ++
 drivers/mailbox/Makefile          |   2 +
 drivers/mailbox/arm-smc-mailbox.c | 168 ++++++++++++++++++++++++++++++++++++++
 3 files changed, 177 insertions(+)
 create mode 100644 drivers/mailbox/arm-smc-mailbox.c

diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig
index ab4eb750bbdd..7707ee26251a 100644
--- a/drivers/mailbox/Kconfig
+++ b/drivers/mailbox/Kconfig
@@ -16,6 +16,13 @@ config ARM_MHU
 	  The controller has 3 mailbox channels, the last of which can be
 	  used in Secure mode only.
 
+config ARM_SMC_MBOX
+	tristate "Generic ARM smc mailbox"
+	depends on OF && HAVE_ARM_SMCCC
+	help
+	  Generic mailbox driver which uses ARM smc calls to call into
+	  firmware for triggering mailboxes.
+
 config IMX_MBOX
 	tristate "i.MX Mailbox"
 	depends on ARCH_MXC || COMPILE_TEST
diff --git a/drivers/mailbox/Makefile b/drivers/mailbox/Makefile
index c22fad6f696b..93918a84c91b 100644
--- a/drivers/mailbox/Makefile
+++ b/drivers/mailbox/Makefile
@@ -7,6 +7,8 @@ obj-$(CONFIG_MAILBOX_TEST)	+= mailbox-test.o
 
 obj-$(CONFIG_ARM_MHU)	+= arm_mhu.o
 
+obj-$(CONFIG_ARM_SMC_MBOX)	+= arm-smc-mailbox.o
+
 obj-$(CONFIG_IMX_MBOX)	+= imx-mailbox.o
 
 obj-$(CONFIG_ARMADA_37XX_RWTM_MBOX)	+= armada-37xx-rwtm-mailbox.o
diff --git a/drivers/mailbox/arm-smc-mailbox.c b/drivers/mailbox/arm-smc-mailbox.c
new file mode 100644
index 000000000000..664c8b4a0ed0
--- /dev/null
+++ b/drivers/mailbox/arm-smc-mailbox.c
@@ -0,0 +1,168 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2016,2017 ARM Ltd.
+ * Copyright 2019 NXP
+ */
+
+#include <linux/arm-smccc.h>
+#include <linux/device.h>
+#include <linux/kernel.h>
+#include <linux/interrupt.h>
+#include <linux/mailbox_controller.h>
+#include <linux/mailbox/arm-smccc-mbox.h>
+#include <linux/module.h>
+#include <linux/platform_device.h>
+
+struct arm_smc_chan_data {
+	unsigned int function_id;
+};
+
+typedef unsigned long (smc_mbox_fn)(unsigned int, unsigned long,
+				    unsigned long, unsigned long,
+				    unsigned long, unsigned long,
+				    unsigned long);
+static smc_mbox_fn *invoke_smc_mbox_fn;
+
+static int arm_smc_send_data(struct mbox_chan *link, void *data)
+{
+	struct arm_smc_chan_data *chan_data = link->con_priv;
+	struct arm_smccc_mbox_cmd *cmd = data;
+	unsigned long ret;
+	u32 function_id;
+
+	function_id = chan_data->function_id;
+	if (!function_id)
+		function_id = cmd->function_id;
+
+	if (ARM_SMCCC_IS_64(function_id)) {
+		ret = invoke_smc_mbox_fn(function_id, cmd->args_smccc64[0],
+					 cmd->args_smccc64[1],
+					 cmd->args_smccc64[2],
+					 cmd->args_smccc64[3],
+					 cmd->args_smccc64[4],
+					 cmd->args_smccc64[5]);
+	} else {
+		ret = invoke_smc_mbox_fn(function_id, cmd->args_smccc32[0],
+					 cmd->args_smccc32[1],
+					 cmd->args_smccc32[2],
+					 cmd->args_smccc32[3],
+					 cmd->args_smccc32[4],
+					 cmd->args_smccc32[5]);
+	}
+
+	mbox_chan_received_data(link, (void *)ret);
+
+	return 0;
+}
+
+static unsigned long __invoke_fn_hvc(unsigned int function_id,
+				     unsigned long arg0, unsigned long arg1,
+				     unsigned long arg2, unsigned long arg3,
+				     unsigned long arg4, unsigned long arg5)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_hvc(function_id, arg0, arg1, arg2, arg3, arg4,
+		      arg5, 0, &res);
+	return res.a0;
+}
+
+static unsigned long __invoke_fn_smc(unsigned int function_id,
+				     unsigned long arg0, unsigned long arg1,
+				     unsigned long arg2, unsigned long arg3,
+				     unsigned long arg4, unsigned long arg5)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(function_id, arg0, arg1, arg2, arg3, arg4,
+		      arg5, 0, &res);
+	return res.a0;
+}
+
+static const struct mbox_chan_ops arm_smc_mbox_chan_ops = {
+	.send_data	= arm_smc_send_data,
+};
+
+static struct mbox_chan *
+arm_smc_mbox_of_xlate(struct mbox_controller *mbox,
+		      const struct of_phandle_args *sp)
+{
+	return mbox->chans;
+}
+
+static int arm_smc_mbox_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct mbox_controller *mbox;
+	struct arm_smc_chan_data *chan_data;
+	int ret;
+	u32 function_id = 0;
+
+	if (of_device_is_compatible(dev->of_node, "arm,smc-mbox"))
+		invoke_smc_mbox_fn = __invoke_fn_smc;
+	else
+		invoke_smc_mbox_fn = __invoke_fn_hvc;
+
+	mbox = devm_kzalloc(dev, sizeof(*mbox), GFP_KERNEL);
+	if (!mbox)
+		return -ENOMEM;
+
+	mbox->of_xlate = arm_smc_mbox_of_xlate;
+	mbox->num_chans = 1;
+	mbox->chans = devm_kzalloc(dev, sizeof(*mbox->chans), GFP_KERNEL);
+	if (!mbox->chans)
+		return -ENOMEM;
+
+	chan_data = devm_kzalloc(dev, sizeof(*chan_data), GFP_KERNEL);
+	if (!chan_data)
+		return -ENOMEM;
+
+	of_property_read_u32(dev->of_node, "arm,func-id", &function_id);
+	chan_data->function_id = function_id;
+
+	mbox->chans->con_priv = chan_data;
+
+	mbox->txdone_poll = false;
+	mbox->txdone_irq = false;
+	mbox->ops = &arm_smc_mbox_chan_ops;
+	mbox->dev = dev;
+
+	platform_set_drvdata(pdev, mbox);
+
+	ret = devm_mbox_controller_register(dev, mbox);
+	if (ret)
+		return ret;
+
+	dev_info(dev, "ARM SMC mailbox enabled.\n");
+
+	return ret;
+}
+
+static int arm_smc_mbox_remove(struct platform_device *pdev)
+{
+	struct mbox_controller *mbox = platform_get_drvdata(pdev);
+
+	mbox_controller_unregister(mbox);
+	return 0;
+}
+
+static const struct of_device_id arm_smc_mbox_of_match[] = {
+	{ .compatible = "arm,smc-mbox", },
+	{ .compatible = "arm,hvc-mbox", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, arm_smc_mbox_of_match);
+
+static struct platform_driver arm_smc_mbox_driver = {
+	.driver = {
+		.name = "arm-smc-mbox",
+		.of_match_table = arm_smc_mbox_of_match,
+	},
+	.probe		= arm_smc_mbox_probe,
+	.remove		= arm_smc_mbox_remove,
+};
+module_platform_driver(arm_smc_mbox_driver);
+
+MODULE_AUTHOR("Peng Fan <peng.fan@nxp.com>");
+MODULE_DESCRIPTION("Generic ARM smc mailbox driver");
+MODULE_LICENSE("GPL v2");
-- 
2.16.4


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Re: [PATCH V7 2/2] mailbox: introduce ARM SMC based mailbox

[kbuild test robot]

[-- Attachment #1: Type: text/plain, Size: 1547 bytes --]

Hi Peng,

Thank you for the patch! Yet something to improve:

[auto build test ERROR on linus/master]
[cannot apply to v5.3 next-20190920]
[if your patch is applied to the wrong git tree, please drop us a note to help
improve the system. BTW, we also suggest to use '--base' option to specify the
base tree in git format-patch, please see https://stackoverflow.com/a/37406982]

url:    https://github.com/0day-ci/linux/commits/Peng-Fan/mailbox-arm-introduce-smc-triggered-mailbox/20190923-143902
config: arm-allmodconfig (attached as .config)
compiler: arm-linux-gnueabi-gcc (GCC) 7.4.0
reproduce:
        wget https://raw.githubusercontent.com/intel/lkp-tests/master/sbin/make.cross -O ~/bin/make.cross
        chmod +x ~/bin/make.cross
        # save the attached .config to linux build tree
        GCC_VERSION=7.4.0 make.cross ARCH=arm 

If you fix the issue, kindly add following tag
Reported-by: kbuild test robot <lkp@intel.com>

All errors (new ones prefixed by >>):

>> drivers/mailbox/arm-smc-mailbox.c:12:10: fatal error: linux/mailbox/arm-smccc-mbox.h: No such file or directory
    #include <linux/mailbox/arm-smccc-mbox.h>
             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
   compilation terminated.

vim +12 drivers/mailbox/arm-smc-mailbox.c

  > 12	#include <linux/mailbox/arm-smccc-mbox.h>
    13	#include <linux/module.h>
    14	#include <linux/platform_device.h>
    15	

---
0-DAY kernel test infrastructure                Open Source Technology Center
https://lists.01.org/pipermail/kbuild-all                   Intel Corporation

[-- Attachment #2: .config.gz --]
[-- Type: application/gzip, Size: 71865 bytes --]

[-- Attachment #3: Type: text/plain, Size: 176 bytes --]

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Re: [PATCH V7 0/2] mailbox: arm: introduce smc triggered mailbox

[André Przywara]

On 23/09/2019 07:36, Peng Fan wrote:

Hi Peng,

thanks for the update!

> From: Peng Fan <peng.fan@nxp.com>
> 
> V7:
> Typo fix
> #mbox-cells changed to 0
> Add a new header file arm-smccc-mbox.h
> Use ARM_SMCCC_IS_64
> 
> Andre,
>   The function_id is still kept in arm_smccc_mbox_cmd, because arm,func-id
> property is optional, so clients could pass function_id to mbox driver.

Well, to be honest, this is the main thing I am opposing:

It should *not* be optional.

The controller driver DT node should *always* contain the function ID.
The reasons for that I explained in the other emails to Jassi:
We can't safely execute smc calls from the Linux kernel, unless we also
comply with the SMCCC standard. So we should not leave the choice of the
function ID to the mailbox client.
Also this much better separates the mailbox controller driver from the
client.

So I think we should reach an agreement here.

Cheers,
Andre

> V6:
> Switch to per-channel a mbox controller
> Drop arm,num-chans, transports, method
> Add arm,hvc-mbox compatible
> Fix smc/hvc args, drop client id and use correct type.
> https://patchwork.kernel.org/cover/11146641/
> 
> V5:
> yaml fix
> https://patchwork.kernel.org/cover/11117741/
> 
> V4:
> yaml fix for num-chans in patch 1/2.
> https://patchwork.kernel.org/cover/11116521/
> 
> V3:
> Drop interrupt
> Introduce transports for mem/reg usage
> Add chan-id for mem usage
> Convert to yaml format
> https://patchwork.kernel.org/cover/11043541/
>  
> V2:
> This is a modified version from Andre Przywara's patch series
> https://lore.kernel.org/patchwork/cover/812997/.
> The modification are mostly:
> Introduce arm,num-chans
> Introduce arm_smccc_mbox_cmd
> txdone_poll and txdone_irq are both set to false
> arm,func-ids are kept, but as an optional property.
> Rewords SCPI to SCMI, because I am trying SCMI over SMC, not SCPI.
> Introduce interrupts notification.
> 
> [1] is a draft implementation of i.MX8MM SCMI ATF implementation that
> use smc as mailbox, power/clk is included, but only part of clk has been
> implemented to work with hardware, power domain only supports get name
> for now.
> 
> The traditional Linux mailbox mechanism uses some kind of dedicated hardware
> IP to signal a condition to some other processing unit, typically a dedicated
> management processor.
> This mailbox feature is used for instance by the SCMI protocol to signal a
> request for some action to be taken by the management processor.
> However some SoCs does not have a dedicated management core to provide
> those services. In order to service TEE and to avoid linux shutdown
> power and clock that used by TEE, need let firmware to handle power
> and clock, the firmware here is ARM Trusted Firmware that could also
> run SCMI service.
> 
> The existing SCMI implementation uses a rather flexible shared memory
> region to communicate commands and their parameters, it still requires a
> mailbox to actually trigger the action.
> 
> This patch series provides a Linux mailbox compatible service which uses
> smc calls to invoke firmware code, for instance taking care of SCMI requests.
> The actual requests are still communicated using the standard SCMI way of
> shared memory regions, but a dedicated mailbox hardware IP can be replaced via
> this new driver.
> 
> This simple driver uses the architected SMC calling convention to trigger
> firmware services, also allows for using "HVC" calls to call into hypervisors
> or firmware layers running in the EL2 exception level.
> 
> Patch 1 contains the device tree binding documentation, patch 2 introduces
> the actual mailbox driver.
> 
> Please note that this driver just provides a generic mailbox mechanism,
> It could support synchronous TX/RX, or synchronous TX with asynchronous
> RX. And while providing SCMI services was the reason for this exercise,
> this driver is in no way bound to this use case, but can be used generically
> where the OS wants to signal a mailbox condition to firmware or a
> hypervisor.
> Also the driver is in no way meant to replace any existing firmware
> interface, but actually to complement existing interfaces.
> 
> [1] https://github.com/MrVan/arm-trusted-firmware/tree/scmi
> 
> 
> 
> Peng Fan (2):
>   dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox
>   mailbox: introduce ARM SMC based mailbox
> 
>  .../devicetree/bindings/mailbox/arm-smc.yaml       |  95 ++++++++++++
>  drivers/mailbox/Kconfig                            |   7 +
>  drivers/mailbox/Makefile                           |   2 +
>  drivers/mailbox/arm-smc-mailbox.c                  | 168 +++++++++++++++++++++
>  4 files changed, 272 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/mailbox/arm-smc.yaml
>  create mode 100644 drivers/mailbox/arm-smc-mailbox.c
> 


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RE: [PATCH V7 0/2] mailbox: arm: introduce smc triggered mailbox

[Peng Fan]

Hi Andre,

> Subject: Re: [PATCH V7 0/2] mailbox: arm: introduce smc triggered mailbox
> 
> On 23/09/2019 07:36, Peng Fan wrote:
> 
> Hi Peng,
> 
> thanks for the update!
> 
> > From: Peng Fan <peng.fan@nxp.com>
> >
> > V7:
> > Typo fix
> > #mbox-cells changed to 0
> > Add a new header file arm-smccc-mbox.h Use ARM_SMCCC_IS_64
> >
> > Andre,
> >   The function_id is still kept in arm_smccc_mbox_cmd, because
> > arm,func-id property is optional, so clients could pass function_id to mbox
> driver.
> 
> Well, to be honest, this is the main thing I am opposing:
> 
> It should *not* be optional.
> 
> The controller driver DT node should *always* contain the function ID.
> The reasons for that I explained in the other emails to Jassi:
> We can't safely execute smc calls from the Linux kernel, unless we also
> comply with the SMCCC standard. So we should not leave the choice of the
> function ID to the mailbox client.
> Also this much better separates the mailbox controller driver from the client.
> 
> So I think we should reach an agreement here.

I am ok to mark it as a required property in v9, but I am not sure Jassi accept it.

Thanks,
Peng.

> 
> Cheers,
> Andre
> 
> > V6:
> > Switch to per-channel a mbox controller Drop arm,num-chans,
> > transports, method Add arm,hvc-mbox compatible Fix smc/hvc args, drop
> > client id and use correct type.
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> >
> hwork.kernel.org%2Fcover%2F11146641%2F&amp;data=02%7C01%7Cpeng.f
> an%40n
> >
> xp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea1d3bc2b4c6fa9
> 2cd99c5c
> >
> 301635%7C0%7C0%7C637048990507177346&amp;sdata=N%2BWdEXh9QXn
> F4cn2DjCwHk
> > qpD1JxtP%2BBfQwn3E3lzYs%3D&amp;reserved=0
> >
> > V5:
> > yaml fix
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> >
> hwork.kernel.org%2Fcover%2F11117741%2F&amp;data=02%7C01%7Cpeng.f
> an%40n
> >
> xp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea1d3bc2b4c6fa9
> 2cd99c5c
> >
> 301635%7C0%7C0%7C637048990507177346&amp;sdata=XcRM%2FH4ZQAU
> QmT%2FDlGzq
> > 93LjlVhUYuvEmdYSezivTog%3D&amp;reserved=0
> >
> > V4:
> > yaml fix for num-chans in patch 1/2.
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> >
> hwork.kernel.org%2Fcover%2F11116521%2F&amp;data=02%7C01%7Cpeng.f
> an%40n
> >
> xp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea1d3bc2b4c6fa9
> 2cd99c5c
> >
> 301635%7C0%7C0%7C637048990507177346&amp;sdata=8f0Etfnd29Q6LHx
> bymLVyvEE
> > 7ElGZzN3uVMcIL%2BmZNQ%3D&amp;reserved=0
> >
> > V3:
> > Drop interrupt
> > Introduce transports for mem/reg usage Add chan-id for mem usage
> > Convert to yaml format
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatc
> >
> hwork.kernel.org%2Fcover%2F11043541%2F&amp;data=02%7C01%7Cpeng.f
> an%40n
> >
> xp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea1d3bc2b4c6fa9
> 2cd99c5c
> >
> 301635%7C0%7C0%7C637048990507177346&amp;sdata=U2%2BjaU06Iu0h
> ULuCz0RT1r
> > vhSfjsu%2BWuKzjTfY7MuNw%3D&amp;reserved=0
> >
> > V2:
> > This is a modified version from Andre Przywara's patch series
> >
> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.ke
> rnel.org%2Fpatchwork%2Fcover%2F812997%2F&amp;data=02%7C01%7Cpe
> ng.fan%40nxp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea1d3
> bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637048990507177346&amp;sda
> ta=dku%2BfT%2BDLilVU5T0fdHMzuUi4DYCM7aV1FQB4vaKCVE%3D&amp;re
> served=0.
> > The modification are mostly:
> > Introduce arm,num-chans
> > Introduce arm_smccc_mbox_cmd
> > txdone_poll and txdone_irq are both set to false arm,func-ids are
> > kept, but as an optional property.
> > Rewords SCPI to SCMI, because I am trying SCMI over SMC, not SCPI.
> > Introduce interrupts notification.
> >
> > [1] is a draft implementation of i.MX8MM SCMI ATF implementation that
> > use smc as mailbox, power/clk is included, but only part of clk has
> > been implemented to work with hardware, power domain only supports get
> > name for now.
> >
> > The traditional Linux mailbox mechanism uses some kind of dedicated
> > hardware IP to signal a condition to some other processing unit,
> > typically a dedicated management processor.
> > This mailbox feature is used for instance by the SCMI protocol to
> > signal a request for some action to be taken by the management processor.
> > However some SoCs does not have a dedicated management core to
> provide
> > those services. In order to service TEE and to avoid linux shutdown
> > power and clock that used by TEE, need let firmware to handle power
> > and clock, the firmware here is ARM Trusted Firmware that could also
> > run SCMI service.
> >
> > The existing SCMI implementation uses a rather flexible shared memory
> > region to communicate commands and their parameters, it still requires
> > a mailbox to actually trigger the action.
> >
> > This patch series provides a Linux mailbox compatible service which
> > uses smc calls to invoke firmware code, for instance taking care of SCMI
> requests.
> > The actual requests are still communicated using the standard SCMI way
> > of shared memory regions, but a dedicated mailbox hardware IP can be
> > replaced via this new driver.
> >
> > This simple driver uses the architected SMC calling convention to
> > trigger firmware services, also allows for using "HVC" calls to call
> > into hypervisors or firmware layers running in the EL2 exception level.
> >
> > Patch 1 contains the device tree binding documentation, patch 2
> > introduces the actual mailbox driver.
> >
> > Please note that this driver just provides a generic mailbox
> > mechanism, It could support synchronous TX/RX, or synchronous TX with
> > asynchronous RX. And while providing SCMI services was the reason for
> > this exercise, this driver is in no way bound to this use case, but
> > can be used generically where the OS wants to signal a mailbox
> > condition to firmware or a hypervisor.
> > Also the driver is in no way meant to replace any existing firmware
> > interface, but actually to complement existing interfaces.
> >
> > [1]
> > https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgith
> >
> ub.com%2FMrVan%2Farm-trusted-firmware%2Ftree%2Fscmi&amp;data=02
> %7C01%7
> >
> Cpeng.fan%40nxp.com%7C52d7e331c222426852a508d740ae7d42%7C686ea
> 1d3bc2b4
> >
> c6fa92cd99c5c301635%7C0%7C0%7C637048990507177346&amp;sdata=fFE
> KK8jYap5
> > igpH6ESGTHYfnhBZMsL2zB%2BdykMdOPwg%3D&amp;reserved=0
> >
> >
> >
> > Peng Fan (2):
> >   dt-bindings: mailbox: add binding doc for the ARM SMC/HVC mailbox
> >   mailbox: introduce ARM SMC based mailbox
> >
> >  .../devicetree/bindings/mailbox/arm-smc.yaml       |  95
> ++++++++++++
> >  drivers/mailbox/Kconfig                            |   7 +
> >  drivers/mailbox/Makefile                           |   2 +
> >  drivers/mailbox/arm-smc-mailbox.c                  | 168
> +++++++++++++++++++++
> >  4 files changed, 272 insertions(+)
> >  create mode 100644
> > Documentation/devicetree/bindings/mailbox/arm-smc.yaml
> >  create mode 100644 drivers/mailbox/arm-smc-mailbox.c
> >

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