Re: [PATCH v3 06/13] mmc: tmio-mmc: define device-tree bindings

[Guennadi Liakhovetski <g.liakhovetski@gmx.de>]

On Thu, 7 Feb 2013, Simon Horman wrote:

> On Wed, Feb 06, 2013 at 10:24:20PM +0000, Arnd Bergmann wrote:
> > On Wednesday 06 February 2013, Guennadi Liakhovetski wrote:
> > > +* Toshiba Mobile IO SD/MMC controller
> > > +
> > > +The tmio-mmc driver doesn't probe its devices actively, instead its binding to
> > > +devices is managed by either MFD drivers or by the sh_mobile_sdhi platform
> > > +driver. Those drivers supply the tmio-mmc driver with platform data, that either
> > > +describe hardware capabilities, known to them, or are obtained by them from
> > > +their own platform data or from their DT information. In the latter case all
> > > +compulsory and any optional properties, common to all SD/MMC drivers, as
> > > +described in mmc.txt, should or can be used. Additionally the following optional
> > > +bindings can be used. They set respective TMIO_MMC_* flags.
> > > +
> > > +Optional properties:
> > > +- toshiba,mmc-wrprotect-disable        : set TMIO_MMC_WRPROTECT_DISABLE flag
> > > +- toshiba,mmc-blksz-2bytes     : set TMIO_MMC_BLKSZ_2BYTES
> > > +- toshiba,mmc-has-idle-wait    : set TMIO_MMC_HAS_IDLE_WAIT
> > 
> > Please write the binding in a way that does not refer to a specific
> > implementation in Linux: The binding should describe the hardware
> > independent of details in the driver. In particular, I think you
> > should not refer to the TMIO_MMC_BLKSZ_2BYTES etc macros but describe
> > in text what the flags are about.
> > 
> > Regarding the toshiba,mmc-wrprotect-disable property, would it be
> > enough to just check the presence of the wp-gpios property?
> > 
> > TMIO_MMC_BLKSZ_2BYTES seems to be set unconditionally in
> > sh_mobile_sdhi_probe and nowhere else, so I'd assume we don't
> > actually need to provide this here, but can keep that knowledge
> > implicit based on whether we're talking to sh_mobile_sdhi
> > or another tmio_mmc variant.

Can do that, yes.

> > For the other last one, is that actually board specific, or just
> > a feature of a given chip? If we can tell by the SoC, then I'd
> > suggest using separate "compatible" properties instead, and
> > put a bitmask of features into the .data field of the of match
> > table. For all I can tell, SH7372 does not set it, while SH73A0,
> > R8A7740 and R8A7779 always do.
> 
> My understanding is that TMIO_MMC_HAS_IDLE_WAIT can be set based
> on the SoC in use.

So far TMIO_MMC_HAS_IDLE_WAIT is set on

board-kzm9g.c (sh73a0 / AG5)
board-ag5evm.c (sh73a0 / AG5)
board-armadillo800eva.c (r8a7740 / A1)
board-kota2.c (sh73a0 / AG5)
board-marzen.c (r8a7779 / H1)

and isn't set on

board-ap4evb.c (sh7372 / ap4)
board-bonito.c (r8a7740 / a1, SDHI isn't used)
board-mackerel.c (sh7372 / ap4)

So, shall we use a compatible property for this and drop this property? We 
can add later at any time, if needed, which is better, than defining 
something redundant. OTOH I seem to remember, that using SoC-version from 
the "compatible" property was considered by someone inappropriate. Magnus, 
what do you think?

So, if we drop TMIO_MMC_BLKSZ_2BYTES and TMIO_MMC_HAS_IDLE_WAIT, we only 
keep toshiba,mmc-wrprotect-disable to set TMIO_MMC_WRPROTECT_DISABLE? And 
that one is definitely needed, because that even differs between SDHI 
instances on one SoC.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/