Date:   Tue, 5 Mar 2019 03:39:23 +0000
From:   Anson Huang <anson.huang@....com>
To:     Guenter Roeck <linux@...ck-us.net>
CC:     "catalin.marinas@....com" <catalin.marinas@....com>,
        "will.deacon@....com" <will.deacon@....com>,
        "wim@...ux-watchdog.org" <wim@...ux-watchdog.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        Andy Gross <andy.gross@...aro.org>,
        "heiko@...ech.de" <heiko@...ech.de>,
        "horms+renesas@...ge.net.au" <horms+renesas@...ge.net.au>,
        "arnd@...db.de" <arnd@...db.de>, "olof@...om.net" <olof@...om.net>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "jagan@...rulasolutions.com" <jagan@...rulasolutions.com>,
        "enric.balletbo@...labora.com" <enric.balletbo@...labora.com>,
        "marc.w.gonzalez@...e.fr" <marc.w.gonzalez@...e.fr>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-watchdog@...r.kernel.org" <linux-watchdog@...r.kernel.org>,
        dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH V5 1/2] watchdog: imx_sc: Add i.MX system controller
 watchdog support

Hi, Guenter

Best Regards!
Anson Huang

> -----Original Message-----
> From: Guenter Roeck [mailto:groeck7@...il.com] On Behalf Of Guenter
> Roeck
> Sent: 2019年3月4日 21:53
> To: Anson Huang <anson.huang@....com>
> Cc: catalin.marinas@....com; will.deacon@....com; wim@...ux-
> watchdog.org; shawnguo@...nel.org; s.hauer@...gutronix.de;
> kernel@...gutronix.de; festevam@...il.com; Andy Gross
> <andy.gross@...aro.org>; heiko@...ech.de; horms+renesas@...ge.net.au;
> arnd@...db.de; olof@...om.net; bjorn.andersson@...aro.org;
> jagan@...rulasolutions.com; enric.balletbo@...labora.com;
> marc.w.gonzalez@...e.fr; linux-arm-kernel@...ts.infradead.org; linux-
> kernel@...r.kernel.org; linux-watchdog@...r.kernel.org; dl-linux-imx
> <linux-imx@....com>
> Subject: Re: [PATCH V5 1/2] watchdog: imx_sc: Add i.MX system controller
> watchdog support
> 
> On 3/3/19 7:22 PM, Anson Huang wrote:
> > Hi, Guenter
> >
> > Best Regards!
> > Anson Huang
> >
> >> -----Original Message-----
> >> From: Guenter Roeck [mailto:groeck7@...il.com] On Behalf Of Guenter
> >> Roeck
> >> Sent: 2019年3月4日 10:46
> >> To: Anson Huang <anson.huang@....com>
> >> Cc: catalin.marinas@....com; will.deacon@....com; wim@...ux-
> >> watchdog.org; shawnguo@...nel.org; s.hauer@...gutronix.de;
> >> kernel@...gutronix.de; festevam@...il.com; Andy Gross
> >> <andy.gross@...aro.org>; heiko@...ech.de;
> horms+renesas@...ge.net.au;
> >> arnd@...db.de; olof@...om.net; bjorn.andersson@...aro.org;
> >> jagan@...rulasolutions.com; enric.balletbo@...labora.com;
> >> marc.w.gonzalez@...e.fr; linux-arm-kernel@...ts.infradead.org; linux-
> >> kernel@...r.kernel.org; linux-watchdog@...r.kernel.org; dl-linux-imx
> >> <linux-imx@....com>
> >> Subject: Re: [PATCH V5 1/2] watchdog: imx_sc: Add i.MX system
> >> controller watchdog support
> >>
> >> On 3/3/19 5:32 PM, Anson Huang wrote:
> >>> Hi, Guenter
> >>>
> >>> Best Regards!
> >>> Anson Huang
> >>>
> >>>> -----Original Message-----
> >>>> From: Guenter Roeck [mailto:groeck7@...il.com] On Behalf Of
> Guenter
> >>>> Roeck
> >>>> Sent: 2019年3月2日 2:32
> >>>> To: Anson Huang <anson.huang@....com>
> >>>> Cc: catalin.marinas@....com; will.deacon@....com; wim@...ux-
> >>>> watchdog.org; shawnguo@...nel.org; s.hauer@...gutronix.de;
> >>>> kernel@...gutronix.de; festevam@...il.com; Andy Gross
> >>>> <andy.gross@...aro.org>; heiko@...ech.de;
> >> horms+renesas@...ge.net.au;
> >>>> arnd@...db.de; olof@...om.net; bjorn.andersson@...aro.org;
> >>>> jagan@...rulasolutions.com; enric.balletbo@...labora.com;
> >>>> marc.w.gonzalez@...e.fr; linux-arm-kernel@...ts.infradead.org;
> >>>> linux- kernel@...r.kernel.org; linux-watchdog@...r.kernel.org;
> >>>> dl-linux-imx <linux-imx@....com>
> >>>> Subject: Re: [PATCH V5 1/2] watchdog: imx_sc: Add i.MX system
> >>>> controller watchdog support
> >>>>
> >>>> On Fri, Mar 01, 2019 at 06:35:31AM +0000, Anson Huang wrote:
> >>>>> i.MX8QXP is an ARMv8 SoC which has a Cortex-M4 system controller
> >>>>> inside, the system controller is in charge of controlling power,
> >>>>> clock and watchdog etc..
> >>>>>
> >>>>> This patch adds i.MX system controller watchdog driver support,
> >>>>> watchdog operation needs to be done in secure EL3 mode via
> >>>>> ARM-Trusted-Firmware, using SMC call, CPU will trap into
> >>>>> ARM-Trusted-Firmware and then it will request system controller to
> >>>>> do watchdog operation via IPC.
> >>>>>
> >>>>> Signed-off-by: Anson Huang <Anson.Huang@....com>
> >>>>> ---
> >>>>> Changes since V4:
> >>>>> 	- change the module build dependency as depends on IMX_SCU and
> >>>> HAVE_ARM_SMCCC, as this
> >>>>> 	  driver is ONLY for i.MX SoC with SCU inside and it uses ARM SMC call.
> >>>>> ---
> >>>>>    drivers/watchdog/Kconfig      |  14 +++
> >>>>>    drivers/watchdog/Makefile     |   1 +
> >>>>>    drivers/watchdog/imx_sc_wdt.c | 201
> >>>>> ++++++++++++++++++++++++++++++++++++++++++
> >>>>>    3 files changed, 216 insertions(+)
> >>>>>    create mode 100644 drivers/watchdog/imx_sc_wdt.c
> >>>>>
> >>>>> diff --git a/drivers/watchdog/Kconfig b/drivers/watchdog/Kconfig
> >>>>> index
> >>>>> 65c3c42..a6bfa54 100644
> >>>>> --- a/drivers/watchdog/Kconfig
> >>>>> +++ b/drivers/watchdog/Kconfig
> >>>>> @@ -625,6 +625,20 @@ config IMX2_WDT
> >>>>>    	  To compile this driver as a module, choose M here: the
> >>>>>    	  module will be called imx2_wdt.
> >>>>>
> >>>>> +config IMX_SC_WDT
> >>>>> +	tristate "IMX SC Watchdog"
> >>>>> +	depends on IMX_SCU
> >>>>> +	depends on HAVE_ARM_SMCCC
> >>>>> +	select WATCHDOG_CORE
> >>>>> +	help
> >>>>> +	  This is the driver for the system controller watchdog
> >>>>> +	  on the NXP i.MX SoCs with system controller inside.
> >>>>> +	  If you have one of these processors and wish to have
> >>>>> +	  watchdog support enabled, say Y, otherwise say N.
> >>>>> +
> >>>>> +	  To compile this driver as a module, choose M here: the
> >>>>> +	  module will be called imx_sc_wdt.
> >>>>> +
> >>>>>    config UX500_WATCHDOG
> >>>>>    	tristate "ST-Ericsson Ux500 watchdog"
> >>>>>    	depends on MFD_DB8500_PRCMU
> >>>>> diff --git a/drivers/watchdog/Makefile b/drivers/watchdog/Makefile
> >>>>> index 4e78a8c..0c9da63 100644
> >>>>> --- a/drivers/watchdog/Makefile
> >>>>> +++ b/drivers/watchdog/Makefile
> >>>>> @@ -68,6 +68,7 @@ obj-$(CONFIG_NUC900_WATCHDOG) +=
> >>>> nuc900_wdt.o
> >>>>>    obj-$(CONFIG_TS4800_WATCHDOG) += ts4800_wdt.o
> >>>>>    obj-$(CONFIG_TS72XX_WATCHDOG) += ts72xx_wdt.o
> >>>>>    obj-$(CONFIG_IMX2_WDT) += imx2_wdt.o
> >>>>> +obj-$(CONFIG_IMX_SC_WDT) += imx_sc_wdt.o
> >>>>>    obj-$(CONFIG_UX500_WATCHDOG) += ux500_wdt.o
> >>>>>    obj-$(CONFIG_RETU_WATCHDOG) += retu_wdt.o
> >>>>>    obj-$(CONFIG_BCM2835_WDT) += bcm2835_wdt.o diff --git
> >>>>> a/drivers/watchdog/imx_sc_wdt.c b/drivers/watchdog/imx_sc_wdt.c
> >> new
> >>>>> file mode 100644 index 0000000..50b49b2
> >>>>> --- /dev/null
> >>>>> +++ b/drivers/watchdog/imx_sc_wdt.c
> >>>>> @@ -0,0 +1,201 @@
> >>>>> +// SPDX-License-Identifier: GPL-2.0
> >>>>> +/*
> >>>>> + * Copyright 2018-2019 NXP.
> >>>>> + */
> >>>>> +
> >>>>> +#include <linux/arm-smccc.h>
> >>>>> +#include <linux/io.h>
> >>>>> +#include <linux/init.h>
> >>>>> +#include <linux/kernel.h>
> >>>>> +#include <linux/module.h>
> >>>>> +#include <linux/moduleparam.h>
> >>>>> +#include <linux/of.h>
> >>>>
> >>>> Should no longer be needed.
> >>>
> >>> Correct, I will remove it.
> >>>
> >>>>
> >>>>> +#include <linux/platform_device.h> #include <linux/reboot.h>
> >>>>> +#include <linux/watchdog.h>
> >>>>> +
> >>>>> +#define DEFAULT_TIMEOUT 60
> >>>>> +/*
> >>>>> + * Software timer tick implemented in scfw side, support 10ms to
> >>>>> +0xffffffff ms
> >>>>> + * in theory, but for normal case, 1s~128s is enough, you can
> >>>>> +change this max
> >>>>> + * value in case it's not enough.
> >>>>> + */
> >>>>> +#define MAX_TIMEOUT 128
> >>>>> +
> >>>>> +#define IMX_SIP_TIMER			0xC2000002
> >>>>> +#define IMX_SIP_TIMER_START_WDOG		0x01
> >>>>> +#define IMX_SIP_TIMER_STOP_WDOG		0x02
> >>>>> +#define IMX_SIP_TIMER_SET_WDOG_ACT	0x03
> >>>>> +#define IMX_SIP_TIMER_PING_WDOG		0x04
> >>>>> +#define IMX_SIP_TIMER_SET_TIMEOUT_WDOG	0x05
> >>>>> +#define IMX_SIP_TIMER_GET_WDOG_STAT	0x06
> >>>>> +#define IMX_SIP_TIMER_SET_PRETIME_WDOG	0x07
> >>>>> +
> >>>>> +#define SC_TIMER_WDOG_ACTION_PARTITION	0
> >>>>> +
> >>>>> +static bool nowayout = WATCHDOG_NOWAYOUT;
> >>>> module_param(nowayout,
> >>>>> +bool, 0000); MODULE_PARM_DESC(nowayout, "Watchdog cannot be
> >>>> stopped
> >>>>> +once started (default="
> >>>>> +		 __MODULE_STRING(WATCHDOG_NOWAYOUT) ")");
> >>>>> +
> >>>>> +static unsigned int timeout = DEFAULT_TIMEOUT;
> >>>>> +module_param(timeout, uint, 0000); MODULE_PARM_DESC(timeout,
> >>>>> +"Watchdog timeout in
> >>>> seconds
> >>>>> +(default="
> >>>>> +		 __MODULE_STRING(DEFAULT_TIMEOUT) ")");
> >>>>> +
> >>>>> +static struct platform_device *imx_sc_wdt_pdev;
> >>>>> +
> >>>>> +static int imx_sc_wdt_ping(struct watchdog_device *wdog) {
> >>>>> +	struct arm_smccc_res res;
> >>>>> +
> >>>>> +	arm_smccc_smc(IMX_SIP_TIMER,
> IMX_SIP_TIMER_PING_WDOG,
> >>>>> +		      0, 0, 0, 0, 0, 0, &res);
> >>>>> +
> >>>>> +	return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int imx_sc_wdt_start(struct watchdog_device *wdog) {
> >>>>> +	struct arm_smccc_res res;
> >>>>> +
> >>>>> +	arm_smccc_smc(IMX_SIP_TIMER,
> IMX_SIP_TIMER_START_WDOG,
> >>>>> +		      0, 0, 0, 0, 0, 0, &res);
> >>>>> +	if (res.a0)
> >>>>> +		return -EACCES;
> >>>>> +
> >>>>> +	arm_smccc_smc(IMX_SIP_TIMER,
> IMX_SIP_TIMER_SET_WDOG_ACT,
> >>>>> +		      SC_TIMER_WDOG_ACTION_PARTITION,
> >>>>> +		      0, 0, 0, 0, 0, &res);
> >>>>> +	return res.a0 ? -EACCES : 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int imx_sc_wdt_stop(struct watchdog_device *wdog) {
> >>>>> +	struct arm_smccc_res res;
> >>>>> +
> >>>>> +	arm_smccc_smc(IMX_SIP_TIMER,
> IMX_SIP_TIMER_STOP_WDOG,
> >>>>> +		      0, 0, 0, 0, 0, 0, &res);
> >>>>> +
> >>>>> +	return res.a0 ? -EACCES : 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int imx_sc_wdt_set_timeout(struct watchdog_device *wdog,
> >>>>> +				unsigned int timeout)
> >>>>> +{
> >>>>> +	struct arm_smccc_res res;
> >>>>> +
> >>>>> +	wdog->timeout = timeout;
> >>>>> +	arm_smccc_smc(IMX_SIP_TIMER,
> >>>> IMX_SIP_TIMER_SET_TIMEOUT_WDOG,
> >>>>> +		      timeout * 1000, 0, 0, 0, 0, 0, &res);
> >>>>> +
> >>>>> +	return res.a0 ? -EACCES : 0;
> >>>>> +}
> >>>>> +
> >>>>> +static const struct watchdog_ops imx_sc_wdt_ops = {
> >>>>> +	.owner = THIS_MODULE,
> >>>>> +	.start = imx_sc_wdt_start,
> >>>>> +	.stop  = imx_sc_wdt_stop,
> >>>>> +	.ping  = imx_sc_wdt_ping,
> >>>>> +	.set_timeout = imx_sc_wdt_set_timeout, };
> >>>>> +
> >>>>> +static const struct watchdog_info imx_sc_wdt_info = {
> >>>>> +	.identity	= "i.MX SC watchdog timer",
> >>>>> +	.options	= WDIOF_SETTIMEOUT |
> WDIOF_KEEPALIVEPING |
> >>>>> +			  WDIOF_MAGICCLOSE |
> WDIOF_PRETIMEOUT, };
> >>>>> +
> >>>>> +static int imx_sc_wdt_probe(struct platform_device *pdev) {
> >>>>> +	struct watchdog_device *imx_sc_wdd;
> >>>>> +	int ret;
> >>>>> +
> >>>>> +	imx_sc_wdd = devm_kzalloc(&pdev->dev,
> sizeof(*imx_sc_wdd),
> >>>> GFP_KERNEL);
> >>>>> +	if (!imx_sc_wdd)
> >>>>> +		return -ENOMEM;
> >>>>> +
> >>>>> +	platform_set_drvdata(pdev, imx_sc_wdd);
> >>>>> +
> >>>>> +	imx_sc_wdd->info = &imx_sc_wdt_info;
> >>>>> +	imx_sc_wdd->ops = &imx_sc_wdt_ops;
> >>>>> +	imx_sc_wdd->min_timeout = 1;
> >>>>> +	imx_sc_wdd->max_timeout = MAX_TIMEOUT;
> >>>>> +	imx_sc_wdd->parent = &pdev->dev;
> >>>>> +	imx_sc_wdd->timeout = DEFAULT_TIMEOUT;
> >>>>> +
> >>>>> +	ret = watchdog_init_timeout(imx_sc_wdd, timeout, &pdev-
> >dev);
> >>>>> +	if (ret)
> >>>>> +		dev_warn(&pdev->dev, "Failed to set timeout value,
> using
> >>>>> +default\n");
> >>>>> +
> >>>>> +	watchdog_stop_on_reboot(imx_sc_wdd);
> >>>>> +	watchdog_stop_on_unregister(imx_sc_wdd);
> >>>>> +
> >>>>> +	ret = devm_watchdog_register_device(&pdev->dev,
> imx_sc_wdd);
> >>>>> +	if (ret) {
> >>>>> +		dev_err(&pdev->dev, "Failed to register watchdog
> device\n");
> >>>>> +		return ret;
> >>>>> +	}
> >>>>> +
> >>>>> +	return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int __maybe_unused imx_sc_wdt_suspend(struct device *dev)
> {
> >>>>> +	struct watchdog_device *imx_sc_wdd =
> dev_get_drvdata(dev);
> >>>>> +
> >>>>> +	if (watchdog_active(imx_sc_wdd))
> >>>>> +		imx_sc_wdt_stop(imx_sc_wdd);
> >>>>> +
> >>>>> +	return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static int __maybe_unused imx_sc_wdt_resume(struct device *dev) {
> >>>>> +	struct watchdog_device *imx_sc_wdd =
> dev_get_drvdata(dev);
> >>>>> +
> >>>>> +	if (watchdog_active(imx_sc_wdd))
> >>>>> +		imx_sc_wdt_start(imx_sc_wdd);
> >>>>> +
> >>>>> +	return 0;
> >>>>> +}
> >>>>> +
> >>>>> +static SIMPLE_DEV_PM_OPS(imx_sc_wdt_pm_ops,
> >>>>> +			 imx_sc_wdt_suspend, imx_sc_wdt_resume);
> >>>>> +
> >>>>> +static struct platform_driver imx_sc_wdt_driver = {
> >>>>> +	.probe		= imx_sc_wdt_probe,
> >>>>> +	.driver		= {
> >>>>> +		.name	= "imx-sc-wdt",
> >>>>> +		.pm	= &imx_sc_wdt_pm_ops,
> >>>>> +	},
> >>>>> +};
> >>>>> +
> >>>>> +static int __init imx_sc_wdt_init(void) {
> >>>>> +	int ret;
> >>>>> +
> >>>>> +	ret = platform_driver_register(&imx_sc_wdt_driver);
> >>>>> +	if (ret)
> >>>>> +		return ret;
> >>>>> +
> >>>>> +	imx_sc_wdt_pdev = platform_device_register_simple("imx-
> sc-wdt",
> >>>>> +-
> >>>> 1, NULL, 0);
> >>>>> +	if (IS_ERR(imx_sc_wdt_pdev)) {
> >>>>> +		platform_driver_unregister(&imx_sc_wdt_driver);
> >>>>> +		return PTR_ERR(imx_sc_wdt_pdev);
> >>>>> +	}
> >>>>
> >>>> I just realized what you are doing here. So the watchdog will
> >>>> always be instantiated if/when the module is loaded. I don't think
> >>>> that was the idea, and it seems to be risky. What happens if
> >>>> someone loads the module on a system where the watchdog is not
> >>>> supported ? There maye be lots of "Access Denied" errors, or
> something undefined may happen.
> >>>
> >>> I thought the "depends on IMX_SCU" was already added in Kconfig,
> >>> that means the module will be ONLY built with IMX_SCU enabled, and
> >>> watchdog will be always enabled if IMX_SCU is enabled. Is it safe enough?
> >>>
> >> No. The driver will be built with arm64:defconfig, meaning it will be
> >> built for all arm64 systems using defconfig. Any such system will
> >> have the driver installed as module, and nothing will prevent the
> >> user from running modprobe. But even if it wasn't enabled with
> >> defconfig, we must not instantiate the driver on an arbitrary system.
> >>
> >>>>
> >>>> Is everyone on Cc: ok with this ? Is this how we handle
> >>>> instantiations nowadays ?  Or should the driver be instantiated
> >>>> from
> >>>> imx_scu_probe() in drivers/firmware/imx/imx-scu.c ?
> >>>>
> >>>> Sorry if the answer is obvious, but I am still struggling with "no
> >>>> more instantiations through devicetree".
> >>>>
> >>>> If the driver is auto-instantiated when the module is loaded, as
> >>>> currently written, there needs to be some check if it is actually
> >>>> supported, possibly in
> >>>> imx_sc_wdt_init() or, if that is not possible, in the probe function.
> >>>> I don't like that, but it would at least prevent the module from
> >>>> being loaded when the hardware is not supported.
> >>>
> >>> Other modules depend on the IMX_SCU IPC will have defer probe there
> >>> to make sure IMX_SCU driver is ready for IPC handle, since watchdog
> >>> driver ONLY uses ARM SMC but no IPC call, so I did NOT add the defer
> >>> probe handle here, so if adding it can answer your question/concern,
> >>> then I can add it, although I think the dependency in Kconfig should
> >>> be good here. Without SCU firmware ready, the SoC does NOT boot up A
> >> core with ATF/Linux at all.
> >>>
> >> That has nothing to do with deferred probing. My concern is that the
> >> driver will be instantiated just by loading it, no matter if the
> >> hardware supporting it is present or not.
> >>
> >> Having a devicetree node would have prevented that since it
> >> instantiates the child drivers with devm_of_platform_populate() in
> >> imx_scu_probe(). The equivalent is to register the platform device from
> imx_scu_probe().
> >> That is the only means to prevent the driver from being instantiated
> >> where it shouldn't. As mentioned before, I would have preferred the
> >> devicetree method, but having it no longer available doesn't mean
> >> that we should add risky code.
> >>
> >> Maybe you can check in the init function if the 'fsl,imx-scu' node
> >> exists, and instantiate the driver if it does. I don't like that
> >> either, but it would be acceptable to me - and maybe better than
> >> instantiating it manually from imx_scu_probe().
> >
> > OK, I can add check of "fsl,imx-scu" in init function and ONLY
> > instantiate the driver if it exist, since there is no watchdog node in
> > devicetree and "fsl,imx-scu" should be treated as watchdog node, so
> > adding such check also makes some sense, putting it inside SCU driver is
> NOT that good I think, do you agree?
> >
> 
> I dislike both. Putting it into the SCU driver probe function would be more
> appropriate. Putting it into the watchdog driver is worse since it should really
> only be instantiated if (and after) the parent driver is instantiated, and the
> parent driver should be listed as its parent. That will get lost if you put the
> check into the watchdog driver.
> 
> I would suggest to submit the patch for the SCU driver first. If that gets
> rejected by its maintainer, we'll have to do it in the watchdog driver.

Thanks Guenter, I resend the V6 patch to move the watchdog platform device register
to SCU driver probe, to be child of SCU device, let's wait for SCU maintainer's
feedback.

Anson.

> 
> Guenter

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