Re: [PATCH v2 0/4] arm: renesas: Add reset control properties

[Simon Horman <horms@verge.net.au>]

On Thu, Mar 16, 2017 at 03:07:22PM +0100, Geert Uytterhoeven wrote:
> 	Hi Simon, Magnus, Laurent, Morimoto-san,
> 
> This patch series describes the reset control topology for on-SoC devices
> connected to the Renesas Clock Pulse Generator / Module Standby and
> Software Reset module on the R-Car H3 and M3-W, RZ/G1M, and RZ/G1E SoCs.
> 
> Resets usually match the corresponding module clocks.  Exceptions are:
>   - The Display Unit has only 2 resets, one per channel pair, cfr.
>     "[PATCH v2] dt-bindings: drm: rcar-du: Document optional reset
>     properties" (http://www.spinics.net/lists/dri-devel/msg134637.html),
>   - The audio module has resets for the Serial Sound Interfaces only.
>     Adding resets and reset-names properties depends on a DT binding
>     update for renesas,rsnd (note: the DT binding documentation in
>     Documentation/devicetree/bindings/sound/renesas,rsnd.txt doesn't
>     even document clocks and clock-names?).
> Upon request from Laurent for the DU, and upon a DT bindings update
> for rcar_sound, the addition of resets (and reset-names) properties for
> these complex modules is postponed.
> 
> Note that this patch series contains hardware description only.
> Actual reset policy is to be defined and implemented separately.
> Also, this is an optional feature, to be enabled explicitly using
> CONFIG_RESET_CONTROLLER=y.  When enabled, an on-SoC device can be reset
> easily using device_reset(), or by using the reset_control_*() API when
> more fine-grained control is desired.
> 
> Possible use cases are (not exhaustive):
>   - Reset a device before use, to make sure it's in a predefined state, and
>     doesn't depend on earlier configuration by e.g. the boot loader,
>   - Reset a device after detecting an anomaly,
>   - Reset a device to verify suspend/resume is handled correctly by the
>     driver in case the device would be part of a power domain on a
>     different/future SoC.
> 
> Dependencies and impact:
>   - The corresponding driver changes to the CGP/MSSR driver are already
>     present in v4.11-rc1.
>   - These patches have no impact as long as CONFIG_RESET_CONTROLLER=n.
>     However, if CONFIG_RESET_CONTROLLER=y and resets properties are
>     prsesent in DTS, the EHCI and OHCI drivers already deassert reset as
>     part of their initialization sequences, and put the devices back
>     into reset state in case initialization failed, or on unbind.
>     I'm not aware of other relevant drivers already using reset control.

It appears that for arm64 defconfig CONFIG_RESET_CONTROLLER=y is true so
by default there will be a behavioural change on arm64. I'd like to
understand if it is a desirable (or at least not undesirable) change.

> For testing, these patches are also available in the
> topic/renesas-cpg-mssr-reset-dts-v2 branch of my renesas-drivers git
> repository at
> git://git.kernel.org/pub/scm/linux/kernel/git/geert/renesas-drivers.git
> 
> This has been tested on the R-Car Gen3 Salvator-X (H3 and M3-W) and the
> R-Car M2-W (using out-of-tree driver modifications) Koelsch development
> boards, by inspecting device register contents before and after reset,
> and by comparing them with their documented reset values.
> 
> Changes compared to v1:
>   - Break out from "[PATCH 0/8] Renesas CPG/MSSR Reset Control Support"
>     (https://lkml.org/lkml/2017/1/20/336),
>   - Postpone adding resets and reset-names properties for complex
>     devices (du, rcar_sound),
>   - Rebase on top of renesas-devel-20170313-v4.11-rc2,
>   - Add reset properties to recently added device nodes.
> 
> Thanks for applying!
> 
> Geert Uytterhoeven (4):
>   arm64: dts: r8a7795: Add reset control properties
>   arm64: dts: r8a7796: Add reset control properties
>   ARM: dts: r8a7743: Add reset control properties
>   ARM: dts: r8a7745: Add reset control properties
> 
>  arch/arm/boot/dts/r8a7743.dtsi           | 24 +++++++++
>  arch/arm/boot/dts/r8a7745.dtsi           | 24 +++++++++
>  arch/arm64/boot/dts/renesas/r8a7795.dtsi | 93 ++++++++++++++++++++++++++++++++
>  arch/arm64/boot/dts/renesas/r8a7796.dtsi | 46 ++++++++++++++++
>  4 files changed, 187 insertions(+)
> 
> -- 
> 2.7.4
> 
> Gr{oetje,eeting}s,
> 
> 						Geert
> 
> --
> Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org
> 
> In personal conversations with technical people, I call myself a hacker. But
> when I'm talking to journalists I just say "programmer" or something like that.
> 							    -- Linus Torvalds
>