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Date: Tue, 8 Dec 2015 14:07:22 -0800
From: Bjorn Andersson <bjorn.andersson@sonymobile.com>
To: John Stultz <john.stultz@linaro.org>
CC: lkml <linux-kernel@vger.kernel.org>, Rob Herring <robh+dt@kernel.org>,
        Pawel Moll <pawel.moll@arm.com>, Mark Rutland <mark.rutland@arm.com>,
        Ian Campbell <ijc+devicetree@hellion.org.uk>,
        Kumar Gala <galak@codeaurora.org>, Vinay Simha BN <simhavcs@gmail.com>,
        Haojian Zhuang <haojian.zhuang@linaro.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        Android Kernel Team <kernel-team@android.com>, <agross@codeaurora.org>,
        <linux-arm-msm@vger.kernel.org>
Subject: Re: [RFC][PATCH] misc: Introduce reboot_reason driver
Message-ID: <20151208220722.GG4000@usrtlx11787.corpusers.net>
References: <1449610162-30543-1-git-send-email-john.stultz@linaro.org>
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On Tue 08 Dec 13:29 PST 2015, John Stultz wrote:

> This patch adds a basic driver to allow for commands like
> "reboot bootloader" and "reboot recovery" to communicate this
> reboot-reason to the bootloader.
> 
> This is commonly done on Android devices, in order to reboot
> the device into fastboot or recovery mode. It also supports
> custom OEM specific commands, via "reboot oem-<value>".
> 
> This driver pulls the phys memory address from DT as well as
> the magic reason values that are written to the address for
> each mode.
> 
> For an example, this patch also adds the DT support for
> the nexus7 device via its dts (which is not yet upstream).
> 
> Thoughts and feedback would be appreciated!
> 

Good to see some work on this, I want it too :)

I do however think this is Qualcomm specific in its implementation, so
adding Andy and linux-arm-msm.

[..]
> diff --git a/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts b/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> index 5183d18..ee5dcb7 100644
> --- a/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> +++ b/arch/arm/boot/dts/qcom-apq8064-nexus7-flo.dts
> @@ -282,6 +282,15 @@
>  			};
>  		};
>  
> +		reboot_reason: reboot_reason@2a03f65c {
> +			compatible		= "reboot_reason";
> +			reg			= <0x2A03F65C 0x4>;
> +			reason,none		= <0x77665501>;
> +			reason,bootloader	= <0x77665500>;
> +			reason,recovery		= <0x77665502>;
> +			reason,oem		= <0x6f656d00>;
> +		};
> +

This address refers to IMEM, which is shared with a number of other
uses. So I think we should have a simple-mfd (and syscon) with this
within.


I like the fact that you don't hard code the magics in the
implementation, as I've seen additions from multiple places - so perhaps
it should be made even more flexible.

OMAP seems to use strings here instead of magics, but the delivery
mechanism looks to be the same. But I think of this as Qualcomm
specific.

>  		gpio-keys {
>  			compatible = "gpio-keys";
>  			power {
[..]
> diff --git a/drivers/misc/reboot_reason.c b/drivers/misc/reboot_reason.c
[..]
> +
> +static int reboot_reason(struct notifier_block *nb, unsigned long action,
> +								void *data)
> +{
> +	char *cmd = (char *)data;
> +	long reason = reasons[NONE];
> +
> +	if (!reboot_reason_addr)
> +		return NOTIFY_DONE;
> +
> +	if (cmd != NULL) {
> +		if (!strncmp(cmd, "bootloader", 10))
> +			reason = reasons[BOOTLOADER];
> +		else if (!strncmp(cmd, "recovery", 8))
> +			reason = reasons[RECOVERY];
> +		else if (!strncmp(cmd, "oem-", 4)) {
> +			unsigned long code;
> +
> +			if (!kstrtoul(cmd+4, 0, &code))
> +				reason = reasons[OEM] | (code & 0xff);
> +		}
> +	}

In the case where we didn't find a match you should write the "normal"
reason here, otherwise I think you will end up in recovery when recovery
issues a reboot (in Android that is).

> +
> +	if (reason != -1)
> +		writel(reason, reboot_reason_addr);
> +	return NOTIFY_DONE;
> +}
> +
> +static int reboot_reason_probe(struct platform_device *pdev)
> +{
> +	struct resource *res;
> +	u32 val;
> +	int i;
> +
> +	/* initialize the reasons */
> +	for (i = 0; i < MAX_REASONS; i++)
> +		reasons[i] = -1;
> +
> +	/* Try to grab the reason io address */
> +	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> +	reboot_reason_addr = devm_ioremap_resource(&pdev->dev, res);
> +	if (IS_ERR(reboot_reason_addr))
> +		return PTR_ERR(reboot_reason_addr);
> +

Please acquire this memory from a syscon (preferably the the parent
simple-mfd).

> +	/* initialize specified reasons from DT */
> +	if (!of_property_read_u32(pdev->dev.of_node, "reason,none", &val))
> +		reasons[NONE] = val;
> +	if (!of_property_read_u32(pdev->dev.of_node, "reason,bootloader", &val))
> +		reasons[BOOTLOADER] = val;
> +	if (!of_property_read_u32(pdev->dev.of_node, "reason,recovery", &val))
> +		reasons[RECOVERY] = val;
> +	if (!of_property_read_u32(pdev->dev.of_node, "reason,oem", &val))
> +		reasons[OEM] = val;

I would like for this to be less hard coded.

> +
> +	/* Install the notifier */
> +	restart_nb.notifier_call = reboot_reason;
> +	restart_nb.priority = 256;
> +	if (register_restart_handler(&restart_nb)) {
> +		dev_err(&pdev->dev,
> +			"failed to setup restart handler.\n");
> +	}
> +	return 0;
> +}
> +

Regards,
Bjorn
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