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

From: Jassi Brar
Date: Thu Jun 20 2019 - 12:50:27 EST


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://lore.kernel.org/patchwork/patch/812999/
>
> 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]'


> + 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.