linux-kernel - Re: [PATCH 00/58] ARM: at91: rework Atmel TCB drivers

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Message-ID: <20170706064055.GE16144@ulmo.fritz.box>
Date:   Thu, 6 Jul 2017 08:40:55 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:     Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Boris Brezillon <boris.brezillon@...e-electrons.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Antoine Aubert <a.aubert@...rkiz.com>,
        Daniel Lezcano <daniel.lezcano@...aro.org>,
        devicetree@...r.kernel.org,
        Douglas Gilbert <dgilbert@...erlog.com>,
        Fabio Porcedda <fabio.porcedda@...il.com>,
        Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Gregory Hermant <gregory.hermant@...ao-systems.com>,
        Joachim Eastwood <manabian@...il.com>,
        linux-pwm@...r.kernel.org, Marek Vasut <marex@...x.de>,
        Martin Reimann <martin.reimann@...ite.de>,
        Peter Rosin <peda@...ntia.se>,
        Raashid Muhammed <raashidmuhammed@...ogic.com>,
        Rob Herring <robh+dt@...nel.org>,
        Rodolfo Giometti <giometti@...ux.it>,
        Sergio Tanzilli <tanzilli@...esystems.it>,
        Thomas Gleixner <tglx@...utronix.de>,
        Tim Schendekehl <tim.schendekehl@...ite.de>
Subject: Re: [PATCH 00/58] ARM: at91: rework Atmel TCB drivers

On Tue, May 30, 2017 at 11:50:41PM +0200, Alexandre Belloni wrote:
> Hi,
> 
> This series reworks the Atmel Timer counter Block drivers. Those blocks
> each have 3 counters with 2 channels each and can be used for
> multiple functions:
>  - timers
>  - PWMs
>  - Quadrature decoders
>  - Stepper motor counters
> 
> Up until now, each TCB was fully used by each driver, possibly wasting
> counters/channels.
> 
> There is a second issue motivating that rework. Until now, the PIT is
> still used to boot then later in the boot sequence, the clocksource is
> switched to the TCB. This ends up not working well with preempt-rt
> because on some SoCs, the PIT interrupt is shared with the DBGU uart.
> When using preempt-rt the interrupt flags for the PIT and the DBGU end
> up being incompatible.
> 
> The rework breaks the DT ABI. Backward compatibility can be kept by
> keeping tcb_clksrc and atmel_tclib but as AVR32 is now gone from the
> kernel, I don't think it makes much sense to keep them.
> 
> Also, there is no other choice than breaking the mainly unused
> pwm-atmel-tcb binding. Only the kizbox is actually using it.
> 
> I think the bindings are now ok and I hope we can take the DT changes
> for 4.13.

Has anyone volunteered to pick this up? What are the dependencies here
and how did you plan to get this merged?

Thierry

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