RE: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox

[Peng Fan <peng.fan@xxxxxxx>]

Hi Jassi

> Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
> 
> On Mon, Jun 3, 2019 at 3:28 AM <peng.fan@xxxxxxx> wrote:
> >
> > From: Peng Fan <peng.fan@xxxxxxx>
> >
> > 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@xxxxxxx>
> > Signed-off-by: Peng Fan <peng.fan@xxxxxxx>
> > ---
> >
> > 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)
> 
> > +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]'

Missed to reply this comment.

The firmware driver might not have func-id, such as SCMI/SCPI.
So add an optional func-id to let smc mailbox driver could
use smc SiP func id.

Thanks,
Peng.

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