From mboxrd@z Thu Jan 1 00:00:00 1970 From: Lee Jones Subject: Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB Date: Wed, 20 May 2015 07:35:51 +0100 Message-ID: <20150520063551.GD3627@x1> References: <1430761002-9327-1-git-send-email-abrestic@chromium.org> <1430761002-9327-5-git-send-email-abrestic@chromium.org> <20150513143954.GA3394@x1> <55544CC5.9050001@nvidia.com> <20150514074058.GA22418@x1> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: QUOTED-PRINTABLE Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-tegra-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Andrew Bresticker Cc: Jon Hunter , Stephen Warren , Thierry Reding , Alexandre Courbot , "devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-tegra-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , "linux-arm-kernel-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org" , "linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Samuel Ortiz List-Id: linux-tegra@vger.kernel.org On Tue, 19 May 2015, Andrew Bresticker wrote: > Lee, >=20 > On Thu, May 14, 2015 at 10:38 AM, Andrew Bresticker > wrote: > > On Thu, May 14, 2015 at 12:40 AM, Lee Jones = wrote: > >> On Thu, 14 May 2015, Jon Hunter wrote: > >> > >>> Hi Lee, > >>> > >>> On 13/05/15 15:39, Lee Jones wrote: > >>> > On Mon, 04 May 2015, Andrew Bresticker wrote: > >>> > > >>> >> Add a binding document for the XUSB host complex on NVIDIA Teg= ra124 > >>> >> and later SoCs. The XUSB host complex includes a mailbox for > >>> >> communication with the XUSB micro-controller and an xHCI host-= controller. > >>> >> > >>> >> Signed-off-by: Andrew Bresticker > >>> >> Cc: Rob Herring > >>> >> Cc: Pawel Moll > >>> >> Cc: Mark Rutland > >>> >> Cc: Ian Campbell > >>> >> Cc: Kumar Gala > >>> >> Cc: Samuel Ortiz > >>> >> Cc: Lee Jones > >>> >> --- > >>> >> Changes from v7: > >>> >> - Move non-shared resources into child nodes. > >>> >> New for v7. > >>> >> --- > >>> >> .../bindings/mfd/nvidia,tegra124-xusb.txt | 37 +++++= +++++++++++++++++ > >>> >> 1 file changed, 37 insertions(+) > >>> >> create mode 100644 Documentation/devicetree/bindings/mfd/nvid= ia,tegra124-xusb.txt > >>> >> > >>> >> diff --git a/Documentation/devicetree/bindings/mfd/nvidia,tegr= a124-xusb.txt b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-x= usb.txt > >>> >> new file mode 100644 > >>> >> index 0000000..bc50110 > >>> >> --- /dev/null > >>> >> +++ b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xu= sb.txt > >>> >> @@ -0,0 +1,37 @@ > >>> >> +NVIDIA Tegra XUSB host copmlex > >>> >> +=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D > >>> >> + > >>> >> +The XUSB host complex on Tegra124 and later SoCs contains an = xHCI host > >>> >> +controller and a mailbox for communication with the XUSB micr= o-controller. > >>> >> + > >>> >> +Required properties: > >>> >> +-------------------- > >>> >> + - compatible: For Tegra124, must contain "nvidia,tegra124-xu= sb". > >>> >> + Otherwise, must contain '"nvidia,-xusb", "nvidia,teg= ra124-xusb"' > >>> >> + where is tegra132. > >>> >> + - reg: Must contain the base and length of the XUSB FPCI reg= isters. > >>> >> + - ranges: Bus address mapping for the XUSB block. Can be em= pty since the > >>> >> + mapping is 1:1. > >>> >> + - #address-cells: Must be 2. > >>> >> + - #size-cells: Must be 2. > >>> >> + > >>> >> +Example: > >>> >> +-------- > >>> >> + usb@0,70098000 { > >>> >> + compatible =3D "nvidia,tegra124-xusb"; > >>> >> + reg =3D <0x0 0x70098000 0x0 0x1000>; > >>> >> + ranges; > >>> >> + > >>> >> + #address-cells =3D <2>; > >>> >> + #size-cells =3D <2>; > >>> >> + > >>> >> + usb-host@0,70090000 { > >>> >> + compatible =3D "nvidia,tegra124-xhci"; > >>> >> + ... > >>> >> + }; > >>> >> + > >>> >> + mailbox { > >>> >> + compatible =3D "nvidia,tegra124-xusb-mbox"; > >>> >> + ... > >>> >> + }; > >>> > > >>> > This doesn't appear to be a proper MFD. I would have the USB a= nd > >>> > Mailbox devices probe seperately and use a phandle to point the= USB > >>> > device to its Mailbox. > >>> > > >>> > usb@xyz { > >>> > mboxes =3D <&xusb-mailbox, [chan]>; > >>> > }; > >>> > > >>> > >>> I am assuming that Andrew had laid it out like this to reflect th= e hw > >>> structure. The mailbox and xhci controller are part of the xusb > >>> sub-system and hence appear as child nodes. My understanding is t= hat for > >>> device-tree we want the device-tree structure to reflect the actu= al hw. > >>> Is this not the case? > >> > >> Yes, the DT files should reflect h/w. I have requested to see wha= t > >> the memory map looks like, so I might provide a more appropriate > >> solution to accepting a pretty pointless MFD. > > > > FWIW, the address map for XUSB looks like this: > > > > XUSB_HOST: 0x70090000 - 0x7009a000 > > xHCI registers: 0x70090000 - 0x70098000 > > FPCI configuration registers: 0x70098000 - 0x70099000 > > IPFS configuration registers: 0x70099000 - 0x7009a000 > > > >> Two solutions spring to mind. You can either call > >> of_platform_populate() from the USB driver, as some already do: > >> > >> drivers/usb/dwc3/dwc3-exynos.c: > >> ret =3D of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-keystone.c: > >> error =3D of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-omap.c: > >> ret =3D of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-qcom.c: > >> ret =3D of_platform_populate(node, NULL, NULL, qdwc->dev); > >> drivers/usb/dwc3/dwc3-st.c: > >> ret =3D of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/musb/musb_am335x.c: > >> ret =3D of_platform_populate(pdev->dev.of_node, NULL, NULL, &p= dev->dev); > > > > This still requires a small, separate driver to setup the regmap an= d > > do of_platform_populate(). The only difference is it lives in > > drivers/usb/ instead of drivers/mfd/. > > > >> Or use the "simple-mfd", which is currently in -next: > >> > >> git show next/master:Documentation/devicetree/bindings/mfd/mfd.t= xt > > > > I'm not too opposed to this, but Thierry was when I brought this up > > before. The issue here is that if we ever have to do something > > besides setting up a regmap in the MFD, we'd have to change the > > binding and break DT backwards-compatibility. >=20 > Any thoughts on this? A minimal MFD seems to be the best way to > future-proof this binding/driver should it need to be extended in the > future. If this is a firm NAK from you however, I'll need to let > Jassi now so that he can un-queue the mailbox patches for 4.2.... I was waiting to hear Thierry's thoughts. However, I am unconvinced that you need an MFD driver for this and refuse to take a shell (read "pointless") one on an "if we ever ..." clause. Will you break backwards capability though? I'm not sure you will. Old DTBs will still use 'simple-mfd' and probe the devices in the normal way. *If* you introduce an MFD driver at a later date then the old DTB will miss out the *new* functionality, which is expected and accepted. --=20 Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org =E2=94=82 Open source software for ARM SoCs =46ollow Linaro: Facebook | Twitter | Blog From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752261AbbETGgB (ORCPT ); Wed, 20 May 2015 02:36:01 -0400 Received: from mail-wi0-f174.google.com ([209.85.212.174]:33920 "EHLO mail-wi0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751574AbbETGf4 (ORCPT ); Wed, 20 May 2015 02:35:56 -0400 Date: Wed, 20 May 2015 07:35:51 +0100 From: Lee Jones To: Andrew Bresticker Cc: Jon Hunter , Stephen Warren , Thierry Reding , Alexandre Courbot , "devicetree@vger.kernel.org" , "linux-tegra@vger.kernel.org" , "linux-usb@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" , "linux-kernel@vger.kernel.org" , Rob Herring , Pawel Moll , Mark Rutland , Ian Campbell , Kumar Gala , Samuel Ortiz Subject: Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB Message-ID: <20150520063551.GD3627@x1> References: <1430761002-9327-1-git-send-email-abrestic@chromium.org> <1430761002-9327-5-git-send-email-abrestic@chromium.org> <20150513143954.GA3394@x1> <55544CC5.9050001@nvidia.com> <20150514074058.GA22418@x1> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 19 May 2015, Andrew Bresticker wrote: > Lee, > > On Thu, May 14, 2015 at 10:38 AM, Andrew Bresticker > wrote: > > On Thu, May 14, 2015 at 12:40 AM, Lee Jones wrote: > >> On Thu, 14 May 2015, Jon Hunter wrote: > >> > >>> Hi Lee, > >>> > >>> On 13/05/15 15:39, Lee Jones wrote: > >>> > On Mon, 04 May 2015, Andrew Bresticker wrote: > >>> > > >>> >> Add a binding document for the XUSB host complex on NVIDIA Tegra124 > >>> >> and later SoCs. The XUSB host complex includes a mailbox for > >>> >> communication with the XUSB micro-controller and an xHCI host-controller. > >>> >> > >>> >> Signed-off-by: Andrew Bresticker > >>> >> Cc: Rob Herring > >>> >> Cc: Pawel Moll > >>> >> Cc: Mark Rutland > >>> >> Cc: Ian Campbell > >>> >> Cc: Kumar Gala > >>> >> Cc: Samuel Ortiz > >>> >> Cc: Lee Jones > >>> >> --- > >>> >> Changes from v7: > >>> >> - Move non-shared resources into child nodes. > >>> >> New for v7. > >>> >> --- > >>> >> .../bindings/mfd/nvidia,tegra124-xusb.txt | 37 ++++++++++++++++++++++ > >>> >> 1 file changed, 37 insertions(+) > >>> >> create mode 100644 Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> > >>> >> diff --git a/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> new file mode 100644 > >>> >> index 0000000..bc50110 > >>> >> --- /dev/null > >>> >> +++ b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> @@ -0,0 +1,37 @@ > >>> >> +NVIDIA Tegra XUSB host copmlex > >>> >> +============================== > >>> >> + > >>> >> +The XUSB host complex on Tegra124 and later SoCs contains an xHCI host > >>> >> +controller and a mailbox for communication with the XUSB micro-controller. > >>> >> + > >>> >> +Required properties: > >>> >> +-------------------- > >>> >> + - compatible: For Tegra124, must contain "nvidia,tegra124-xusb". > >>> >> + Otherwise, must contain '"nvidia,-xusb", "nvidia,tegra124-xusb"' > >>> >> + where is tegra132. > >>> >> + - reg: Must contain the base and length of the XUSB FPCI registers. > >>> >> + - ranges: Bus address mapping for the XUSB block. Can be empty since the > >>> >> + mapping is 1:1. > >>> >> + - #address-cells: Must be 2. > >>> >> + - #size-cells: Must be 2. > >>> >> + > >>> >> +Example: > >>> >> +-------- > >>> >> + usb@0,70098000 { > >>> >> + compatible = "nvidia,tegra124-xusb"; > >>> >> + reg = <0x0 0x70098000 0x0 0x1000>; > >>> >> + ranges; > >>> >> + > >>> >> + #address-cells = <2>; > >>> >> + #size-cells = <2>; > >>> >> + > >>> >> + usb-host@0,70090000 { > >>> >> + compatible = "nvidia,tegra124-xhci"; > >>> >> + ... > >>> >> + }; > >>> >> + > >>> >> + mailbox { > >>> >> + compatible = "nvidia,tegra124-xusb-mbox"; > >>> >> + ... > >>> >> + }; > >>> > > >>> > This doesn't appear to be a proper MFD. I would have the USB and > >>> > Mailbox devices probe seperately and use a phandle to point the USB > >>> > device to its Mailbox. > >>> > > >>> > usb@xyz { > >>> > mboxes = <&xusb-mailbox, [chan]>; > >>> > }; > >>> > > >>> > >>> I am assuming that Andrew had laid it out like this to reflect the hw > >>> structure. The mailbox and xhci controller are part of the xusb > >>> sub-system and hence appear as child nodes. My understanding is that for > >>> device-tree we want the device-tree structure to reflect the actual hw. > >>> Is this not the case? > >> > >> Yes, the DT files should reflect h/w. I have requested to see what > >> the memory map looks like, so I might provide a more appropriate > >> solution to accepting a pretty pointless MFD. > > > > FWIW, the address map for XUSB looks like this: > > > > XUSB_HOST: 0x70090000 - 0x7009a000 > > xHCI registers: 0x70090000 - 0x70098000 > > FPCI configuration registers: 0x70098000 - 0x70099000 > > IPFS configuration registers: 0x70099000 - 0x7009a000 > > > >> Two solutions spring to mind. You can either call > >> of_platform_populate() from the USB driver, as some already do: > >> > >> drivers/usb/dwc3/dwc3-exynos.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-keystone.c: > >> error = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-omap.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-qcom.c: > >> ret = of_platform_populate(node, NULL, NULL, qdwc->dev); > >> drivers/usb/dwc3/dwc3-st.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/musb/musb_am335x.c: > >> ret = of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev); > > > > This still requires a small, separate driver to setup the regmap and > > do of_platform_populate(). The only difference is it lives in > > drivers/usb/ instead of drivers/mfd/. > > > >> Or use the "simple-mfd", which is currently in -next: > >> > >> git show next/master:Documentation/devicetree/bindings/mfd/mfd.txt > > > > I'm not too opposed to this, but Thierry was when I brought this up > > before. The issue here is that if we ever have to do something > > besides setting up a regmap in the MFD, we'd have to change the > > binding and break DT backwards-compatibility. > > Any thoughts on this? A minimal MFD seems to be the best way to > future-proof this binding/driver should it need to be extended in the > future. If this is a firm NAK from you however, I'll need to let > Jassi now so that he can un-queue the mailbox patches for 4.2.... I was waiting to hear Thierry's thoughts. However, I am unconvinced that you need an MFD driver for this and refuse to take a shell (read "pointless") one on an "if we ever ..." clause. Will you break backwards capability though? I'm not sure you will. Old DTBs will still use 'simple-mfd' and probe the devices in the normal way. *If* you introduce an MFD driver at a later date then the old DTB will miss out the *new* functionality, which is expected and accepted. -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org │ Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog From mboxrd@z Thu Jan 1 00:00:00 1970 From: lee.jones@linaro.org (Lee Jones) Date: Wed, 20 May 2015 07:35:51 +0100 Subject: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB In-Reply-To: References: <1430761002-9327-1-git-send-email-abrestic@chromium.org> <1430761002-9327-5-git-send-email-abrestic@chromium.org> <20150513143954.GA3394@x1> <55544CC5.9050001@nvidia.com> <20150514074058.GA22418@x1> Message-ID: <20150520063551.GD3627@x1> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, 19 May 2015, Andrew Bresticker wrote: > Lee, > > On Thu, May 14, 2015 at 10:38 AM, Andrew Bresticker > wrote: > > On Thu, May 14, 2015 at 12:40 AM, Lee Jones wrote: > >> On Thu, 14 May 2015, Jon Hunter wrote: > >> > >>> Hi Lee, > >>> > >>> On 13/05/15 15:39, Lee Jones wrote: > >>> > On Mon, 04 May 2015, Andrew Bresticker wrote: > >>> > > >>> >> Add a binding document for the XUSB host complex on NVIDIA Tegra124 > >>> >> and later SoCs. The XUSB host complex includes a mailbox for > >>> >> communication with the XUSB micro-controller and an xHCI host-controller. > >>> >> > >>> >> Signed-off-by: Andrew Bresticker > >>> >> Cc: Rob Herring > >>> >> Cc: Pawel Moll > >>> >> Cc: Mark Rutland > >>> >> Cc: Ian Campbell > >>> >> Cc: Kumar Gala > >>> >> Cc: Samuel Ortiz > >>> >> Cc: Lee Jones > >>> >> --- > >>> >> Changes from v7: > >>> >> - Move non-shared resources into child nodes. > >>> >> New for v7. > >>> >> --- > >>> >> .../bindings/mfd/nvidia,tegra124-xusb.txt | 37 ++++++++++++++++++++++ > >>> >> 1 file changed, 37 insertions(+) > >>> >> create mode 100644 Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> > >>> >> diff --git a/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> new file mode 100644 > >>> >> index 0000000..bc50110 > >>> >> --- /dev/null > >>> >> +++ b/Documentation/devicetree/bindings/mfd/nvidia,tegra124-xusb.txt > >>> >> @@ -0,0 +1,37 @@ > >>> >> +NVIDIA Tegra XUSB host copmlex > >>> >> +============================== > >>> >> + > >>> >> +The XUSB host complex on Tegra124 and later SoCs contains an xHCI host > >>> >> +controller and a mailbox for communication with the XUSB micro-controller. > >>> >> + > >>> >> +Required properties: > >>> >> +-------------------- > >>> >> + - compatible: For Tegra124, must contain "nvidia,tegra124-xusb". > >>> >> + Otherwise, must contain '"nvidia,-xusb", "nvidia,tegra124-xusb"' > >>> >> + where is tegra132. > >>> >> + - reg: Must contain the base and length of the XUSB FPCI registers. > >>> >> + - ranges: Bus address mapping for the XUSB block. Can be empty since the > >>> >> + mapping is 1:1. > >>> >> + - #address-cells: Must be 2. > >>> >> + - #size-cells: Must be 2. > >>> >> + > >>> >> +Example: > >>> >> +-------- > >>> >> + usb at 0,70098000 { > >>> >> + compatible = "nvidia,tegra124-xusb"; > >>> >> + reg = <0x0 0x70098000 0x0 0x1000>; > >>> >> + ranges; > >>> >> + > >>> >> + #address-cells = <2>; > >>> >> + #size-cells = <2>; > >>> >> + > >>> >> + usb-host at 0,70090000 { > >>> >> + compatible = "nvidia,tegra124-xhci"; > >>> >> + ... > >>> >> + }; > >>> >> + > >>> >> + mailbox { > >>> >> + compatible = "nvidia,tegra124-xusb-mbox"; > >>> >> + ... > >>> >> + }; > >>> > > >>> > This doesn't appear to be a proper MFD. I would have the USB and > >>> > Mailbox devices probe seperately and use a phandle to point the USB > >>> > device to its Mailbox. > >>> > > >>> > usb at xyz { > >>> > mboxes = <&xusb-mailbox, [chan]>; > >>> > }; > >>> > > >>> > >>> I am assuming that Andrew had laid it out like this to reflect the hw > >>> structure. The mailbox and xhci controller are part of the xusb > >>> sub-system and hence appear as child nodes. My understanding is that for > >>> device-tree we want the device-tree structure to reflect the actual hw. > >>> Is this not the case? > >> > >> Yes, the DT files should reflect h/w. I have requested to see what > >> the memory map looks like, so I might provide a more appropriate > >> solution to accepting a pretty pointless MFD. > > > > FWIW, the address map for XUSB looks like this: > > > > XUSB_HOST: 0x70090000 - 0x7009a000 > > xHCI registers: 0x70090000 - 0x70098000 > > FPCI configuration registers: 0x70098000 - 0x70099000 > > IPFS configuration registers: 0x70099000 - 0x7009a000 > > > >> Two solutions spring to mind. You can either call > >> of_platform_populate() from the USB driver, as some already do: > >> > >> drivers/usb/dwc3/dwc3-exynos.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-keystone.c: > >> error = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-omap.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/dwc3/dwc3-qcom.c: > >> ret = of_platform_populate(node, NULL, NULL, qdwc->dev); > >> drivers/usb/dwc3/dwc3-st.c: > >> ret = of_platform_populate(node, NULL, NULL, dev); > >> drivers/usb/musb/musb_am335x.c: > >> ret = of_platform_populate(pdev->dev.of_node, NULL, NULL, &pdev->dev); > > > > This still requires a small, separate driver to setup the regmap and > > do of_platform_populate(). The only difference is it lives in > > drivers/usb/ instead of drivers/mfd/. > > > >> Or use the "simple-mfd", which is currently in -next: > >> > >> git show next/master:Documentation/devicetree/bindings/mfd/mfd.txt > > > > I'm not too opposed to this, but Thierry was when I brought this up > > before. The issue here is that if we ever have to do something > > besides setting up a regmap in the MFD, we'd have to change the > > binding and break DT backwards-compatibility. > > Any thoughts on this? A minimal MFD seems to be the best way to > future-proof this binding/driver should it need to be extended in the > future. If this is a firm NAK from you however, I'll need to let > Jassi now so that he can un-queue the mailbox patches for 4.2.... I was waiting to hear Thierry's thoughts. However, I am unconvinced that you need an MFD driver for this and refuse to take a shell (read "pointless") one on an "if we ever ..." clause. Will you break backwards capability though? I'm not sure you will. Old DTBs will still use 'simple-mfd' and probe the devices in the normal way. *If* you introduce an MFD driver at a later date then the old DTB will miss out the *new* functionality, which is expected and accepted. -- Lee Jones Linaro STMicroelectronics Landing Team Lead Linaro.org ? Open source software for ARM SoCs Follow Linaro: Facebook | Twitter | Blog