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

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Date:   Tue, 20 Nov 2018 13:34:03 -0800
From:   Eric Anholt <eric@...olt.net>
To:     Stefan Wahren <stefan.wahren@...e.com>,
        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

Stefan Wahren <stefan.wahren@...e.com> writes:

> 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.

I consider your "advantage" to be a disadvantage.  By forcing the split,
you end up having more driver files to manage, more platform devices,
and more error-prone code to get the resources from the parent down into
the client.  It feels like writing software for the sake of writing
software, rather than solving a concrete problem.

My original series:

 10 files changed, 951 insertions(+), 273 deletions(-)

The MFD series:

 12 files changed, 882 insertions(+), 25 deletions(-)

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