RE: [PATCH V6 2/2] mailbox: introduce ARM SMC based mailbox

Peng Fan
2019-09-18T09:09:31Z

Hi Andre,

> Subject: Re: [PATCH V6 2/2] mailbox: introduce ARM SMC based mailbox
>
> On Mon, 16 Sep 2019 09:44:41 +0000
> Peng Fan <peng.fan@nxp.com> wrote:
>
> Hi,
>
> looks quite good now, some smaller comments below.
> I think the only thing left is the "function ID passed by the client" topic.
>
> Have you tried using this interface using hvc, for instance in KVM or Xen? For

No. I do not have that implementation in hypervisor.

> instance to provide access to a clock for a passed-through platform device?
> Another use case that pops up from time to time is GPIO for guests. This
> sounds like a use case for using the register interface, also we could use the
> hvc return value.
>
> > 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://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore
> > .kernel.org%2Fpatchwork%2Fpatch%2F812999%2F&amp;data=02%7C01%7
> Cpeng.fa
> >
> n%40nxp.com%7C58a1ed4078264d14958f08d73b95ed7e%7C686ea1d3bc2b
> 4c6fa92cd
> >
> 99c5c301635%7C0%7C1%7C637043387484474825&amp;sdata=Cp1zlhlpQbg
> BsWu9ZDV
> > RKkXmd6kvUR%2BtPO7EPR7YLpA%3D&amp;reserved=0
> >
> > 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 | 167
> > ++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 176 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..c84aef39c8d9
> > --- /dev/null
> > +++ b/drivers/mailbox/arm-smc-mailbox.c
> > @@ -0,0 +1,167 @@
> > +// 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/module.h>
> > +#include <linux/platform_device.h>
> > +
> > +struct arm_smc_chan_data {
> > + unsigned int function_id;
> > +};
> > +
> > +struct arm_smccc_mbox_cmd {
> > + unsigned int function_id;
> > + union {
> > + unsigned int args_smccc32[6];
> > + unsigned long args_smccc64[6];
>
> Shouldn't this be u32 and u64 here, as the data type has this explicit length in
> the SMCCC?

ok

>
> > + };
> > +};
>
> If this is the data structure that this mailbox controller uses, I would expect
> this to be documented somewhere, or even exported.

Export this structure in include/linux/mailbox/smc-mailbox.h?

>
> And again, I don't like the idea of having the function ID in here.

You mean function_id in arm_smccc_mbox_cmd is not good?

>
> > +
> > +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 (function_id & BIT(30)) {
>
> if (ARM_SMCCC_IS_64(function_id)) {

ok

>
> > + 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 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->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;
>
> Don't we need to provide something to confirm reception to the client? In our
> case we can set this as soon as the smc/hvc returns.

As smc/hvc returns, it means the transfer is over and receive is done.

Thanks,
Peng.

>
> Cheers,
> Andre.
>
> > + 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");