linux-kernel - Re: [PATCH 03/11] Documentation: mmc: sdhci-of-arasan: Add soc-ctl-syscon for corecfg regs

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Date:	Wed, 8 Jun 2016 15:17:29 -0500
From:	Rob Herring <robh@...nel.org>
To:	Douglas Anderson <dianders@...omium.org>
Cc:	ulf.hansson@...aro.org, kishon@...com,
	Heiko Stuebner <heiko@...ech.de>, shawn.lin@...k-chips.com,
	xzy.xu@...k-chips.com, briannorris@...omium.org,
	adrian.hunter@...el.com, linux-rockchip@...ts.infradead.org,
	linux-mmc@...r.kernel.org, devicetree@...r.kernel.org,
	pawel.moll@....com, mark.rutland@....com,
	ijc+devicetree@...lion.org.uk, galak@...eaurora.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 03/11] Documentation: mmc: sdhci-of-arasan: Add
 soc-ctl-syscon for corecfg regs

On Tue, Jun 07, 2016 at 03:44:36PM -0700, Douglas Anderson wrote:
> As can be seen in Arasan's datasheet [1] there are several "corecfg"
> settings in their SDHCI IP Block that are supposed to be controlled by
> software.  Although the datasheet referenced is a bit vague about how to
> access corecfg, in Figure 5 you can see that for Arasan's PHY (a
> separate component than their SDHCI component) they describe the
> "phyctrl" registers as being "FROM SOC CTL REG", implying that it's up
> to the licensee of the Arasan IP block to implement these registers.  It
> seems sane to assume that the "corecfg" registers in their SDHCI IP
> block works in a similar way for all licensees of the IP Block.
> 
> Device tree has a model that allows a device to get a reference to
> random registers located elsewhere in the SoC: sysctl.  Let's leverage
> this model and allow adding a sysctl reference to access the control
> registers for the Arasan SDHCI PHYs.
> 
> Having a reference to the control registers doesn't do much for us on
> its own since the Arasan spec doesn't specify how these corecfg values
> are laid out in memory.  In the SDHCI driver we'll need a map detailing
> where each corecfg can be found in each implementation.  This map can be
> found using the primary compatible string of the SDHCI device.  In that
> spirit, document that existing rk3399 device trees already have a
> specific compatible string, though up to now they've always been relying
> on the driver supporting the generic.
> 
> Note that since existing devices seem to work fairly well as-is, we'll
> list the syscon reference as "optional", but it's likely that we'll run
> into much fewer problems if we can actually set the proper values in the
> syscon, so it is strongly suggested that any SoCs where we have a map to
> set the corecfg also include a reference to the syscon.
> 
> [1]: https://arasan.com/wp-content/media/eMMC-5-1-Total-Solution_Rev-1-3.pdf
> 
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>  .../devicetree/bindings/mmc/arasan,sdhci.txt       | 27 ++++++++++++++++++++--
>  1 file changed, 25 insertions(+), 2 deletions(-)

Acked-by: Rob Herring <robh@...nel.org>