Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753065AbbF3UXO (ORCPT ); Tue, 30 Jun 2015 16:23:14 -0400 Received: from mail-wi0-f170.google.com ([209.85.212.170]:33188 "EHLO mail-wi0-f170.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752171AbbF3UWg (ORCPT ); Tue, 30 Jun 2015 16:22:36 -0400 From: Grant Likely Subject: Re: [PATCH v8 4/9] mfd: Add binding document for NVIDIA Tegra XUSB To: Lee Jones , Thierry Reding Cc: Mark Rutland , Alexandre Courbot , Ian Campbell , "linux-usb@vger.kernel.org" , Samuel Ortiz , Pawel Moll , "devicetree@vger.kernel.org" , Andrew Bresticker , Stephen Warren , "linux-kernel@vger.kernel.org" , Jon Hunter , Rob Herring , Kumar Gala , "linux-tegra@vger.kernel.org" , "linux-arm-kernel@lists.infradead.org" In-Reply-To: <20150526151854.GP11677@x1> References: <1430761002-9327-5-git-send-email-abrestic@chromium.org> <20150513143954.GA3394@x1> <55544CC5.9050001@nvidia.com> <20150514074058.GA22418@x1> <20150520063551.GD3627@x1> <20150520145227.GA3787@ulmo.nvidia.com> <20150521084001.GB6310@x1> <20150521101247.GA8073@ulmo.nvidia.com> <20150526151854.GP11677@x1> Date: Tue, 30 Jun 2015 19:22:39 +0100 Message-Id: <20150630182239.66694C407D8@trevor.secretlab.ca> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 12681 Lines: 245 On Tue, 26 May 2015 16:18:54 +0100 , Lee Jones wrote: > On Thu, 21 May 2015, Thierry Reding wrote: > > > On Thu, May 21, 2015 at 09:40:01AM +0100, Lee Jones wrote: > > > On Wed, 20 May 2015, Thierry Reding wrote: > > > > On Wed, May 20, 2015 at 07:35:51AM +0100, Lee Jones wrote: > > > > > On Tue, 19 May 2015, Andrew Bresticker wrote: > > > > > > 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: > > > > > > >>> 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. > > > > > > > > I'm a little confused by the simple-mfd approach. The only code I see in > > > > linux-next for this is a single line that adds the "simple-mfd" string > > > > to the OF device ID table in drivers/of/platform.c. As far as I can tell > > > > this will merely cause child devices to be created. There won't be a > > > > shared regmap and resources won't be set up properly either. Having a > > > > proper MFD driver seems to be the only way to achieve what we need. > > > > > > > > The reason why every other simple-mfd users seems to get away with this > > > > is because they also match on syscon and that sets up a regmap of its > > > > own and the child device drivers use the syscon API to get at it. So I > > > > don't see how we can make use of simple-mfd to achieve what we need, > > > > unless we essentially copy what syscon does (but do proper resource > > > > management while at it). > > > > > > If you have shared resources and your device isn't classed as a syscon > > > device then yes, simple-mfd probably isn't suitable for this use-case. > > > You might need to go into more detail with regards to "proper resource > > > management", as I'm not entirely sure I agree. > > > > > > Still, this doesn't change the fact that, from what I've seen, I still > > > don't think you need a dedicated MFD driver. > > > > > > What do you think of: > > > > > > usb-host@0,70090000 { > > > compatible = "nvidia,tegra124-xhci"; > > > reg = <0x0 0x70090000 0x0 0x80CF>, > > > <0x0 0x70098800 0x0 0x0800>, > > > <0x0 0x70099000 0x0 0x1000>; > > > > > > /* Something from the datasheet */ > > > reg-names = "xhci-before-mbox", "xhci-after-mbox", "ipfs"; > > > > > > interrupts = ; > > > ranges; > > > > > > xusb_mbox: mailbox { > > > compatible = "nvidia,tegra124-xusb-mbox"; > > > reg = <0x0 0x700980e0 0x0 0x13>, > > > <0x0 0x70098428 0x0 0x03>; > > > > > > /* Something from the datasheet */ > > > reg-names = "mbox-one", "mbox-two"; > > > interrupts = ; > > > }; > > > }; > > > > > > Then hvae the XHCI driver call of_platform_populate() as I proposed > > > above? > > > > That's a little bonghits. It requires the drivers to jump through hoops > > to properly manage register accesses (needs to differentiate on the base > > depending on the register offset). So if you're going to NAK the MFD > > approach I'd rather go a completely different route and keep only a top- > > level node in DT here. > > > > One of the problems that the MFD design tries to solve is that the XHCI > > controller needs a reference to the mailbox and the pad controller for a > > PHY. The pad controller at the same time requires a reference to the > > mailbox, so we have a circular dependency that we can only resolve by > > introducing two separate devices, instantiated by some top-level entity. > > For that reason I don't think your proposal is going to work either. The > > circular dependency can't be broken because the XHCI driver will not be > > able to of_platform_populate() before getting a PHY, and the PHY will > > never show up until of_platform_populate() is called. > > > > So if this isn't going to be an MFD, then I think we should simply go > > and instantiate platform devices from the XUSB driver directly. The > > problem arising from that is that we have no place to put the top-level > > driver. We could take it into drivers/soc/tegra, or perhaps even have it > > in the XHCI driver. > > > > If we instantiate platform devices we can either set up the resources > > such that we don't have to jump through hoops (I think the resource tree > > will allow that) or set up a shared regmap. The latter might be the > > easier way out, though it'd also be copying much of what MFD does, but > > so be it if that's the only way we can get the matter settled. > > I understand the difficulties identified and empathise with your > situation. I just can't bring myself to justify that a USB device > which has it's own Mailbox is an MFD. If you take a look above, you > can see some examples of other USB drivers registering sub-devices. I > think you can make this work well for your setup. Not using MFD I would say is completely justified. I think too many devices try to get shoehorned into MFD when there really isn't a need for it. g. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/