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

From: Sudeep Holla <sudeep.holla@arm.com>
To: Jassi Brar <jassisinghbrar@gmail.com>
Cc: Mark Rutland <mark.rutland@arm.com>,
	Devicetree List <devicetree@vger.kernel.org>,
	Peng Fan <peng.fan@nxp.com>,
	Florian Fainelli <f.fainelli@gmail.com>,
	"festevam@gmail.com" <festevam@gmail.com>,
	Sudeep Holla <sudeep.holla@arm.com>,
	Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
	Rob Herring <robh+dt@kernel.org>,
	dl-linux-imx <linux-imx@nxp.com>, ",
	Sascha Hauer" <kernel@pengutronix.de>,
	Andre Przywara <andre.przywara@arm.com>,
	"van.freenix@gmail.com" <van.freenix@gmail.com>,
	Shawn Guo <shawnguo@kernel.org>,
	"linux-arm-kernel@lists.infradead.org"
	<linux-arm-kernel@lists.infradead.org>
Subject: Re: [PATCH V2 2/2] mailbox: introduce ARM SMC based mailbox
Date: Thu, 27 Jun 2019 10:09:03 +0100	[thread overview]
Message-ID: <20190627090903.GD13572@e107155-lin> (raw)
In-Reply-To: <CABb+yY2B_bGqZhd3HRm2qOwGNXG8UYvRo0_uBmwGbx_1gA-vfA@mail.gmail.com>

On Wed, Jun 26, 2019 at 01:27:41PM -0500, Jassi Brar wrote:
> On Wed, Jun 26, 2019 at 11:44 AM Florian Fainelli <f.fainelli@gmail.com> wrote:
> >
> > On 6/26/19 6:31 AM, Peng Fan wrote:
> > >>> 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.
> > >>>
> > >> There is no end to conforming to protocols. Controller drivers should
> > >> be written having no particular client in mind.
> > >
> > > If the func-id needs be passed from user, then the chan_id suggested
> > > by Sudeep should also be passed from user, not in mailbox driver.
> > >
> > > Jassi, so from your point, arm_smc_send_data just send a0 - a6
> > > to firmware, right?
> > >
> > > Sudeep, Andre, Florian,
> > >
> > > What's your suggestion? SCMI not support, do you have
> > > plan to add smc transport in SCMI?
> >
> > On the platforms that I work with, we have taken the liberty of
> > implementing SCMI in our monitor firmware because the other MCU we use
> > for dynamic voltage and frequency scaling did not have enough memory to
> > support that and we still had the ability to make that firmware be
> > trusted enough we could give it power management responsibilities. I
> > would certainly feel more comfortable if the SCMI specification was
> > amended to indicate that the Agent could be such a software entity,
> > still residing on the same host CPU as the Platform(s), but if not,
> > that's fine.
> >
> > This has lead us to implement a mailbox driver that uses a proprietary
> > SMC call for the P2A path ("tx" channel) and the return being done via
> > either that same SMC or through SGI. You can take a look at it in our
> > downstream tree here actually:
> >
> > https://github.com/Broadcom/stblinux-4.9/blob/master/linux/drivers/mailbox/brcmstb-mailbox.c
> >
> > If we can get rid of our own driver and uses a standard SMC based
> > mailbox driver that supports our use case that involves interrupts (we
> > can always change their kind without our firmware/boot loader since FDT
> > is generated from that component), that would be great.
> >
> static irqreturn_t brcm_isr(void)
> {
>          mbox_chan_received_data(&chans[0], NULL);
>          return IRQ_HANDLED;
> }
> 
> Sorry, I fail to understand why the irq can't be moved inside the
> client driver itself? There can't be more cost to it and there
> definitely is no functionality lost.

What if there are multiple clients ?
And I assume you are referring to case like this where IRQ is not tied
to the mailbox IP.

--
Regards,
Sudeep

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