linux-kernel - Re: [PATCH 0/8] BCM2835 PM driver

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Date:   Tue, 20 Nov 2018 18:49:31 +0100 (CET)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Eric Anholt <eric@...olt.net>,
        Florian Fainelli <f.fainelli@...il.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Wim Van Sebroeck <wim@...ux-watchdog.org>,
        Guenter Roeck <linux@...ck-us.net>,
        linux-watchdog@...r.kernel.org
Cc:     linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        bcm-kernel-feedback-list@...adcom.com
Subject: Re: [PATCH 0/8] BCM2835 PM driver

Hi Eric,

> Eric Anholt <eric@...olt.net> hat am 20. November 2018 um 18:19 geschrieben:
> 
> 
> This series moves the BCM2835 WDT driver that controls a fraction of
> the PM block out to soc/ and adds most of the rest of its
> functionality.  My motivation has been to have V3D be functional
> without firmware calls, probably improve its interactivity (since
> we'll be able to power on/off without RPC to the firmware that may be
> busy with other tasks), and (in a patch not submitted in this series)
> extend its binding to use the reset controller instead of trying to
> reset by toggling its power domain.
> 
> I've tested V3D with a few hours of running a V3D test, sleep(1) (to
> trigger PM domain off); running a GPU hang job (to trigger reset);
> sleep(1).  The non-hanging success-case job always passed, and dmesg
> had no complaints from bcm2835-pm.  The other power domains are not
> tested, but I've done my best.
> 
> This series will probably also be of interest to the
> https://github.com/christinaa/rpi-open-firmware project for enabling USB.
> 

apologize to give you my feedback after you send out the series.

I know you won't be happy about it, but i think we need a little more complex but future proof solution for this power driver. According to the register definition of the PM block, we have multiple functions here (power domains, watchdog, pads/pinctrl, ...). Since this is common for ARM SoCs there is a subsystem called mfd (multi function device) [1] to abstract all resources of the IP block.

This has the advantage that we don't need a monolithic driver which takes care of all functions.

According to this approach we would have the following drivers:
mfd/bcm2835.c
soc/bcm/bcm2835-power.c
watchdog/bcm2835_wdt.c

Best regards
Stefan

[1] - http://events17.linuxfoundation.org/sites/events/files/slides/belloni-mfd-regmap-syscon_0.pdf