linux-kernel - Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox

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Message-ID: <CABb+yY1wW-arSMQSYjrezXOZ0Ar_shAr78MOyUD3hBxXohWx3g@mail.gmail.com>
Date:   Thu, 20 Jun 2019 11:50:12 -0500
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Peng Fan <peng.fan@....com>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Sudeep Holla <sudeep.holla@....com>,
        Florian Fainelli <f.fainelli@...il.com>,
        ", Sascha Hauer" <kernel@...gutronix.de>,
        dl-linux-imx <linux-imx@....com>,
        Shawn Guo <shawnguo@...nel.org>, festevam@...il.com,
        Devicetree List <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Andre Przywara <andre.przywara@....com>, van.freenix@...il.com
Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox

On Mon, Jun 3, 2019 at 3:28 AM <peng.fan@....com> wrote:
>
> From: Peng Fan <peng.fan@....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@....com>
> Signed-off-by: Peng Fan <peng.fan@....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)

> +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.

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