linux-kernel - Re: [RFC 04/10] memory: Add Tegra124 memory controller support

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Date:	Fri, 27 Jun 2014 13:15:16 +0200
From:	Thierry Reding <thierry.reding@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	Rob Herring <robh+dt@...nel.org>, Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Stephen Warren <swarren@...dotorg.org>,
	Will Deacon <will.deacon@....com>,
	Joerg Roedel <joro@...tes.org>,
	Cho KyongHo <pullip.cho@...sung.com>,
	Grant Grundler <grundler@...omium.org>,
	Dave Martin <Dave.Martin@....com>,
	Marc Zyngier <marc.zyngier@....com>,
	Hiroshi Doyu <hdoyu@...dia.com>,
	Olav Haugan <ohaugan@...eaurora.org>,
	Paul Walmsley <pwalmsley@...dia.com>,
	Rhyland Klein <rklein@...dia.com>,
	Allen Martin <amartin@...dia.com>, devicetree@...r.kernel.org,
	iommu@...ts.linux-foundation.org,
	linux-arm-kernel@...ts.infradead.org, linux-tegra@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC 04/10] memory: Add Tegra124 memory controller support

On Fri, Jun 27, 2014 at 01:07:04PM +0200, Arnd Bergmann wrote:
> On Thursday 26 June 2014 22:49:44 Thierry Reding wrote:
> > +static const struct tegra_mc_client tegra124_mc_clients[] = {
> > +       {
> > +               .id = 0x01,
> > +               .name = "display0a",
> > +               .swgroup = TEGRA_SWGROUP_DC,
> > +               .smmu = {
> > +                       .reg = 0x228,
> > +                       .bit = 1,
> > +               },
> > +               .latency = {
> > +                       .reg = 0x2e8,
> > +                       .shift = 0,
> > +                       .mask = 0xff,
> > +                       .def = 0xc2,
> > +               },
> > +       }, {
> 
> This is a rather long table that I assume would need to get duplicated
> and modified for each specific SoC. Have you considered to put the information
> into DT instead, as auxiliary data in the iommu specifier as provided by
> the device?

Most of this data really is register information and I don't think that
belongs in DT. Also since this is fixed for a given SoC and in no way
configurable (well, with the exception of the .def field above) I don't
see any point in parsing this from device tree.

Also only the .smmu substruct is immediately relevant to the IOMMU part
of the driver. The .swgroup field could possibly also be moved into that
substructure since it is only relevant to the IOMMU.

So essentially what this table does is map SWGROUPs (which are provided
in the IOMMU specifier) to the clients and registers that the IOMMU
programming needs. As an analogy it corresponds roughly to the pins and
pingroups tables of pinctrl drivers. Those don't belong in device tree
either.

Thierry

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