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SubjectRE: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
Date
Hi Jassi,

> -----Original Message-----
> From: Jassi Brar [mailto:jassisinghbrar@gmail.com]
> Sent: 2019年6月21日 0:50
> To: Peng Fan <peng.fan@nxp.com>
> Cc: Rob Herring <robh+dt@kernel.org>; Mark Rutland
> <mark.rutland@arm.com>; Sudeep Holla <sudeep.holla@arm.com>; Florian
> Fainelli <f.fainelli@gmail.com>; , Sascha Hauer <kernel@pengutronix.de>;
> dl-linux-imx <linux-imx@nxp.com>; Shawn Guo <shawnguo@kernel.org>;
> festevam@gmail.com; Devicetree List <devicetree@vger.kernel.org>; Linux
> Kernel Mailing List <linux-kernel@vger.kernel.org>;
> linux-arm-kernel@lists.infradead.org; Andre Przywara
> <andre.przywara@arm.com>; van.freenix@gmail.com
> Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
>
> On Mon, Jun 3, 2019 at 3:28 AM <peng.fan@nxp.com> wrote:
> >
> > 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%7C1237677cb01044ad714508d6f59f648f%7C686ea1d3bc2b4
> c6fa92cd
> >
> 99c5c301635%7C0%7C0%7C636966462272457978&amp;sdata=Hzgeu43m5
> ZkeRMtL8Bx
> > gUm3%2B6FBObib1OPHPlSccE%2B0%3D&amp;reserved=0
> >
> > Cc: Andre Przywara <andre.przywara@arm.com>
> > Signed-off-by: Peng Fan <peng.fan@nxp.com>
> > ---
> >
> > V2:
> > Add interrupts notification support.
> >
> > drivers/mailbox/Kconfig | 7 ++
> > drivers/mailbox/Makefile | 2 +
> > drivers/mailbox/arm-smc-mailbox.c | 190
> ++++++++++++++++++++++++++++++++
> > include/linux/mailbox/arm-smc-mailbox.h | 10 ++
> > 4 files changed, 209 insertions(+)
> > create mode 100644 drivers/mailbox/arm-smc-mailbox.c create mode
> > 100644 include/linux/mailbox/arm-smc-mailbox.h
> >
> > diff --git a/drivers/mailbox/Kconfig b/drivers/mailbox/Kconfig index
> > 595542bfae85..c3bd0f1ddcd8 100644
> > --- a/drivers/mailbox/Kconfig
> > +++ b/drivers/mailbox/Kconfig
> > @@ -15,6 +15,13 @@ 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..fef6e38d8b98
> > --- /dev/null
> > +++ b/drivers/mailbox/arm-smc-mailbox.c
> > @@ -0,0 +1,190 @@
> > +// 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-smc-mailbox.h>
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +
> > +#define ARM_SMC_MBOX_USE_HVC BIT(0)
> > +#define ARM_SMC_MBOX_USB_IRQ BIT(1)
> > +
> IRQ bit is unused (and unnecessary IMO)

This will be removed in next version.

>
> > +struct arm_smc_chan_data {
> > + u32 function_id;
> > + u32 flags;
> > + int irq;
> > +};
> > +
> > +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;
> > + struct arm_smccc_res res;
> > + u32 function_id;
> > +
> > + if (chan_data->function_id != UINT_MAX)
> > + function_id = chan_data->function_id;
> > + else
> > + function_id = cmd->a0;
> > +
> Not sure about chan_data->function_id. Why restrict from DT?
> 'a0' is the function_id register, let the user pass func-id via the 'a0' like other
> values via 'a[1-7]'
>
>
> > + if (chan_data->flags & ARM_SMC_MBOX_USE_HVC)
> > + arm_smccc_hvc(function_id, cmd->a1, cmd->a2,
> cmd->a3, cmd->a4,
> > + cmd->a5, cmd->a6, cmd->a7, &res);
> > + else
> > + arm_smccc_smc(function_id, cmd->a1, cmd->a2,
> cmd->a3, cmd->a4,
> > + cmd->a5, cmd->a6, cmd->a7, &res);
> > +
> > + if (chan_data->irq)
> > + return 0;
> > +
> This irq thing seems like oob signalling, that is, a protocol thing.
> And then it provides lesser info via chan_irq_handler (returns NULL) than
> res.a0 - which can always be ignored if not needed.
> So the irq should be implemented in the upper layer if the protocol needs it.

The interrupts was added here because in v1, Florian suggest
"
I would just put a
provision in the binding to support an optional interrupt such that
asynchronism gets reasonably easy to plug in when it is available (and
desirable).
"

So I introduced interrupt in V2. In my testcase, after smc call done,
it means firmware->smc mailbox->firmware done. Interrupt notification
from firmware->Linux, means firmware has done the operation.

When using interrupts, we could not know res.a0 as smc sync call.

Interrupts is not a must in my testcase, Florian, Andre, do you have
any comments? Should I keep interrupts in V3 or drop it as Jassi comments?

Thanks,
Peng.

>
> > + mbox_chan_received_data(link, (void *)res.a0);
> > +
> This is fine.
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