linux-kernel - Re: [PATCH 2/2] watchdog: Add new arm_smc

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Message-ID: <CAODwPW-d_PpV4Jhg2CC+7Tfyrrh=gh6hRfcEKFb4gj+LB6vrWw@mail.gmail.com>
Date:   Fri, 14 Feb 2020 13:32:09 -0800
From:   Julius Werner <jwerner@...omium.org>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Evan Benn <evanbenn@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Julius Werner <jwerner@...omium.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Mauro Carvalho Chehab <mchehab+samsung@...nel.org>,
        Marcin Juszkiewicz <marcin.juszkiewicz@...aro.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Olof Johansson <olof@...om.net>,
        Leonard Crestez <leonard.crestez@....com>,
        Jonathan Cameron <Jonathan.Cameron@...wei.com>,
        Dinh Nguyen <dinguyen@...nel.org>,
        linux-arm-kernel@...ts.infradead.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Will Deacon <will@...nel.org>, linux-watchdog@...r.kernel.org,
        Rob Herring <robh@...nel.org>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Clément Péron <peron.clem@...il.com>,
        Shawn Guo <shawnguo@...nel.org>,
        "David S. Miller" <davem@...emloft.net>,
        Anson Huang <Anson.Huang@....com>
Subject: Re: [PATCH 2/2] watchdog: Add new arm_smc_wdt watchdog driver

> > with a Secure Monitor firmware to forward watchdog operations to
> > firmware via a Secure Monitor Call. This may be useful for platforms
> > using TrustZone that want the Secure Monitor firmware to have the final
> > control over the watchdog.
> >
>
> As written, one would assume this to work on all systems implementing
> ARM secure firmware, which is not the case. Please select a different
> name, and provide information about the systems where this is actually
> supported.
>
> If it happens to be standardized, we will need a reference to the standard
> supported. This needs to distinguish from IMX_SC_WDT, which also supports
> a secure monitor based watchdog (but doesn't claim to be generic).

Back when I wrote this I was hoping it could be something that other
platforms can pick up if they want to, but that hasn't happened yet
and the code on the Trusted Firmware side is still MediaTek-specific.
Unfortunately Arm doesn't make it easy to write generic SMC interfaces
and my attempts to change that haven't been very fruitful for now. So
yes, probably makes sense to treat this as MediaTek-specific for now,
we can still consider expanding it later if there's interest from
other platforms. (I would like to avoid every vendor writing their own
driver and SMC interface for this, although looking at that IMX driver
it seems that we're already there.)