linux-kernel - Re: [PATCH 0/9] Add Reset Controller support for Actions Semi Owl SoCs

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Date:   Mon, 30 Jul 2018 17:38:31 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
        Andreas Färber <afaerber@...e.de>
Cc:     mturquette@...libre.com, sboyd@...nel.org, robh+dt@...nel.org,
        linux-clk@...r.kernel.org, liuwei@...ions-semi.com,
        mp-cs@...ions-semi.com, 96boards@...obotics.com,
        devicetree@...r.kernel.org, daniel.thompson@...aro.org,
        amit.kucheria@...aro.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, hzhang@...obotics.com,
        bdong@...obotics.com, manivannanece23@...il.com,
        thomas.liau@...ions-semi.com, jeff.chen@...ions-semi.com,
        pn@...x.de, edgar.righi@...tec.org.br, sravanhome@...il.com
Subject: Re: [PATCH 0/9] Add Reset Controller support for Actions Semi Owl
 SoCs

On Mon, 2018-07-30 at 20:41 +0530, Manivannan Sadhasivam wrote:
> Hi Andreas,
> 
> On Mon, Jul 30, 2018 at 12:26:07PM +0200, Andreas Färber wrote:
> > Hi Mani,
> > 
> > Am 27.07.2018 um 20:45 schrieb Manivannan Sadhasivam:
> > > This patchset adds Reset Controller (RMU) support for Actions Semi
> > > Owl SoCs, S900 and S700. For the Owl SoCs, RMU has been integrated into
> > > the clock subsystem in hardware. Hence, in software we integrate RMU
> > > support into common clock driver inorder to maintain compatibility.
> > 
> > Can this not be placed into drivers/reset/ by using mfd-simple with a
> > sub-node in DT?
> > 
> 
> Actually I was not sure where to place this reset controller driver. When I
> looked into other similar ones such as sunxi, they just integrated into the
> clk subsystem. So I just chose that path. But yeah, this is hacky!
> 
> But this RMU is not MFD by any means. Since the CMU (Clock) and RMU (Reset)
> are two separate IPs inside SoC, we shouldn't describe it as a MFD driver. Since
> RMU has only 2 registers, the HW designers decided to use up the CMU memory
> map. So, maybe syscon would be best option I think. What is your opinion?

Using syscon seems cleaner than stuffing the regmap into owl_clk_desc.

> Even if we go for syscon, we should place the reset driver within clk
> framework as I can see other SoCs like Mediatek are doing the same. But again
> I'm not sure!

Me neither. If the CMU and RMU are really separate and only share the
memory map, a syscon driver could live in drivers/reset without
problems.
It's only when there are interactions between clocks and resets that you
really want to have the reset driver integrated with clk.

regards
Philipp