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

> Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
>
> On Thu, Jun 20, 2019 at 10:21:09AM +0000, Peng Fan wrote:
> > Hi Sudeep,
> >
> > > Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
> > >
> > > On Mon, Jun 03, 2019 at 04:30:05PM +0800, 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://lore
> > > > .kernel.org%2Fpatchwork%2Fpatch%2F812999%2F&amp;data=02%7C0
> 1%7
> > > Cpeng.fa
> > > >
> > >
> n%40nxp.com%7C6b37f78032e446be750e08d6f560e707%7C686ea1d3bc2b4
> > > c6fa92cd
> > > >
> > >
> 99c5c301635%7C0%7C0%7C636966193913988679&amp;sdata=UNM4MTPs
> > > brqoMqWStEy
> > > > YzzwMEWTmX7hHO3TeNEz%2BOAw%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)
> > > > +
> > > > +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;
> > > > +
> > > > + 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);
> > > > +
> > >
> > > So how will the SMC/HVC handler in EL3/2 find which mailbox is being
> > > referred with this command ? I prefer 2nd argument to be the mailbox
> > > number.
> > You mean channel number as following?
> >
> > @@ -37,10 +38,10 @@ static int arm_smc_send_data(struct mbox_chan
> *link, void *data)
> > function_id = cmd->a0;
> >
> > if (chan_data->flags & ARM_SMC_MBOX_USE_HVC)
> > - arm_smccc_hvc(function_id, cmd->a1, cmd->a2,
> cmd->a3, cmd->a4,
> > + arm_smccc_hvc(function_id, chan_data->chan_id,
> 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,
> > + arm_smccc_smc(function_id, chan_data->chan_id,
> cmd->a2, cmd->a3, cmd->a4,
> > cmd->a5, cmd->a6, cmd->a7, &res);
> >
>
> Yes something like above. There's a brief description of the same in
> latest SCMI specification though it's not related to SCMI, it more
> general note for SMC based mailbox.
>
> "In case the doorbell is SMC/HVC based, it should follow the SMC Calling
> Convention [SMCCC] and needs to provide the identifier of the Shared
> Memory
> area that contains the payload. On return from the call, the Shared Memory
> area which contained the payload is now updated with the SCMI return
> response.
> The identifier of the Shared Memory area should be 32-bits and each
> identifier
> should denote a distinct Shared Memory area."

Thanks for the info, it make sense to pass channel id to firmware.

>
> > Or should that be passed from firmware driver?
> >
>
> No, we can't assume the id's in DT are 1-1 translation to mailbox ID used
> though it may be the same most of the time.

Understand.

>
> > If not from firmware driver, just as above, I do not have a good idea which
> > should be passed to smc, from cmd->a1 to a5 or from cmd->a2 to a6.
> >
>
> Also I found copying those registers may not be always needed and can
> be sub-optimal. May be a way to indicate that this in DT whether
> register based transfers are used or using memory. Just a thought.

"reg-transport" or "mem-transport" should help here.

Thanks,
peng.

>
> --
> Regards,
> Sudeep

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