Re: [rtc-linux] [PATCH 2/5] RTC/i.MX/DryIce: add the unit recovery code

[Alexandre Belloni <alexandre.belloni@free-electrons.com>]

On 14/04/2015 at 11:11:53 +0200, Juergen Borleis wrote :
> This code is requiered to recover the unit from a security violation.
      required ^

> Hopefully this code can recover the unit from a hardware related invalid
> state as well.
> 
> Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
> Signed-off-by: Robert Schwebel <rsc@pengutronix.de>
> [rsc: got NDA clearance from Freescale]
> ---
>  drivers/rtc/rtc-imxdi.c | 333 ++++++++++++++++++++++++++++++++++++++++++------
>  1 file changed, 295 insertions(+), 38 deletions(-)
> 
> diff --git a/drivers/rtc/rtc-imxdi.c b/drivers/rtc/rtc-imxdi.c
> index 8750477..f8abf2b 100644
> --- a/drivers/rtc/rtc-imxdi.c
> +++ b/drivers/rtc/rtc-imxdi.c
> @@ -172,6 +172,296 @@ struct imxdi_dev {
>   * task, we bring back this unit into life.
>   */
>  
> +/* do a write into the unit without interrupt support */
> +static void di_write_busy_wait(const struct imxdi_dev *imxdi, u32 val,
> +								unsigned reg)

Alignment should match the open parenthesis, please fix all occurrences
in your patch.

> +{
> +	/* do the register write */
> +	__raw_writel(val, imxdi->ioaddr + reg);
> +
> +	/*
> +	 * now it takes four 32,768 kHz clock cycles to take
> +	 * the change into effect = 122 us
> +	 */
> +	udelay(200);

As the requirement is not that critical, you may want to use usleep_range()

> +}
> +
> +static void di_report_tamper_info(struct imxdi_dev *imxdi,  u32 dsr)
> +{
> +	u32 dtcr;
> +
> +	dtcr = __raw_readl(imxdi->ioaddr + DTCR);
> +
> +	dev_emerg(&imxdi->pdev->dev, "!! DryIce tamper event detected !!\n");
> +	/* the following flags force a transition into the "FAILURE STATE" */
> +	if (dsr & DSR_VTD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Voltage Tamper event\n");
> +		if (!(dtcr & DTCR_VTE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Voltage Tamper detection wasn't enabled. False positive?\n");

I'm not sure about prefixing all the messages with "!! ". dev_emerg()
seems important enough to be noticed.
I would remove " False positive?". What about
		dev_emerg(&imxdi->pdev->dev,
			  "%sVoltage Tamper event\n",
			  (dtcr & DTCR_VTE) ? "" : "Spurious ");

> +	}
> +	if (dsr & DSR_CTD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! 32768 Hz Clock Tamper Event\n");
> +		if (!(dtcr & DTCR_CTE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Clock Tamper detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_TTD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Temperature Tamper Event\n");
> +		if (!(dtcr & DTCR_TTE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Temperature Tamper detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_SAD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Secure Controller Alarm Event\n");
> +		if (!(dtcr & DTCR_SAIE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Secure Controller Alarm detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_EBD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! External Boot Tamper Event\n");
> +		if (!(dtcr & DTCR_EBE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But External Boot detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_ETAD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! External Tamper A Event\n");
> +		if (!(dtcr & DTCR_ETAE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But External Tamper A wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_ETBD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! External Tamper B Event\n");
> +		if (!(dtcr & DTCR_ETBE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But External Tamper B wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_WTD) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Wire-mesh Tamper Event\n");
> +		if (!(dtcr & DTCR_WTE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But wire-mesh Tamper detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_MCO) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Monotonic-counter Overflow Event\n");
> +		if (!(dtcr & DTCR_MOE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Monotonic-counter Overflow detection wasn't enabled. False positive?\n");
> +	}
> +	if (dsr & DSR_TCO) {
> +		dev_emerg(&imxdi->pdev->dev, "!! Timer-counter Overflow Event\n");
> +		if (!(dtcr & DTCR_TOE))
> +			dev_emerg(&imxdi->pdev->dev,
> +				"!! But Timer-counter Overflow detection wasn't enabled. False positive?\n");
> +	}
> +}
> +
> +static void di_what_is_to_be_done(struct imxdi_dev *imxdi,
> +						const char *power_supply)
> +{
> +	dev_emerg(&imxdi->pdev->dev, " Please cycle the %s power supply in order to get the DryIce unit working again\n",
            remove that heading space ^

I would also explain that the RTC is part of the DryIce unit.

> +			power_supply);
> +}
> +
> +static int di_handle_failure_state(struct imxdi_dev *imxdi, u32 dsr)
> +{
> +	u32 dcr;
> +
> +	dev_dbg(&imxdi->pdev->dev, "DSR register reports: %08X\n", dsr);
> +
> +	/* report the cause */
> +	di_report_tamper_info(imxdi, dsr);
> +
> +	dcr = __raw_readl(imxdi->ioaddr + DCR);

Even if it is used across the whole driver, I would avoid using
__raw_readx as this makes the driver only working in little endian mode.

> +
> +	if (dcr & DCR_FSHL) {
> +		/* we are out of luck */
> +		di_what_is_to_be_done(imxdi, "battery");
> +		return -ENODEV;
> +	}
> +	/*
> +	 * with the next SYSTEM POR we will transit from the "FAILURE STATE"
> +	 * into the "NON-VALID STATE" + "FAILURE STATE"
> +	 */
> +	di_what_is_to_be_done(imxdi, "main");
> +
> +	return -ENODEV;
> +}
> +
> +static int di_handle_valid_state(struct imxdi_dev *imxdi, u32 dsr)
> +{
> +	/* initialize alarm */
> +	di_write_busy_wait(imxdi, DCAMR_UNSET, DCAMR);
> +	di_write_busy_wait(imxdi, 0, DCALR);
> +
> +	/* clear alarm flag */
> +	if (dsr & DSR_CAF)
> +		di_write_busy_wait(imxdi, DSR_CAF, DSR);
> +
> +	return 0;
> +}
> +
> +static int di_handle_invalid_state(struct imxdi_dev *imxdi, u32 dsr)
> +{
> +	u32 dcr, sec;
> +
> +	/*
> +	 * lets disable all sources which can force the DryIce unit into
> +	 * the "FAILURE STATE" for now
> +	 */
> +	di_write_busy_wait(imxdi, 0x00000000, DTCR);
> +	/* and lets protect them at runtime from any change */
> +	di_write_busy_wait(imxdi, DCR_TDCSL, DCR);
> +
> +	sec = __raw_readl(imxdi->ioaddr + DTCMR);
> +	if (sec != 0)
> +		dev_warn(&imxdi->pdev->dev,
> +			"The security violation has happend at %u seconds\n",

Further improvement for this driver: use both DTCMR and DTCLR to be year
2038 proof

> +			sec);
> +	/*
> +	 * the timer cannot be set/modified if
> +	 * - the TCHL or TCSL bit is set in DCR
> +	 */
> +	dcr = __raw_readl(imxdi->ioaddr + DCR);
> +	if (!(dcr & DCR_TCE)) {
> +		if (dcr & DCR_TCHL) {
> +			/* we are out of luck */
> +			di_what_is_to_be_done(imxdi, "battery");
> +			return -ENODEV;
> +		}
> +		if (dcr & DCR_TCSL) {
> +			di_what_is_to_be_done(imxdi, "main");
> +			return -ENODEV;
> +		}
> +
Unnecessary blank line

> +	}
> +	/*
> +	 * - the timer counter stops/is stopped if
> +	 *   - its overflow flag is set (TCO in DSR)
> +	 *      -> clear overflow bit to make it count again
> +	 *   - NVF is set in DSR
> +	 *      -> clear non-valid bit to make it count again
> +	 *   - its TCE (DCR) is cleared
> +	 *      -> set TCE to make it count
> +	 *   - it was never set before
> +	 *      -> write a time into it (required again if the NVF was set)
> +	 */
> +	/* state handled */
> +	di_write_busy_wait(imxdi, DSR_NVF, DSR);
> +	/* clear overflow flag */
> +	di_write_busy_wait(imxdi, DSR_TCO, DSR);
> +	/* enable the counter */
> +	di_write_busy_wait(imxdi, dcr | DCR_TCE, DCR);
> +	/* set and trigger it to make it count */
> +	di_write_busy_wait(imxdi, sec, DTCMR);
> +
> +	/* now prepare for the valid state */
> +	return di_handle_valid_state(imxdi, __raw_readl(imxdi->ioaddr + DSR));
> +}
> +
> +static int di_handle_invalid_and_failure_state(struct imxdi_dev *imxdi, u32 dsr)
> +{
> +	u32 dcr;
> +
> +	/*
> +	 * now we must first remove the tamper sources in order to get the
> +	 * device out of the "FAILURE STATE"
> +	 * To disable any of the following sources we need to modify the DTCR
> +	 */
> +	if (dsr & (DSR_WTD | DSR_ETBD | DSR_ETAD | DSR_EBD | DSR_SAD |
> +			DSR_TTD | DSR_CTD | DSR_VTD | DSR_MCO | DSR_TCO)) {
> +		dcr = __raw_readl(imxdi->ioaddr + DCR);
> +		if (dcr & DCR_TDCHL) {
> +			/*
> +			 * the tamper register is locked. We cannot disable the
> +			 * tamper detection. The TDCHL can only be reset by a
> +			 * DRYICE POR, but we cannot force a DRYICE POR in
> +			 * softwere because we are still in "FAILURE STATE".
> +			 * We need a DRYICE POR via battery power cycling....
> +			 */
> +			/*
> +			 * out of luck!
> +			 * we cannot disable them without a DRYICE POR
> +			 */
> +			di_what_is_to_be_done(imxdi, "battery");
> +			return -ENODEV;
> +		}
> +		if (dcr & DCR_TDCSL) {
> +			/* a soft lock can be removed by a SYSTEM POR */
> +			di_what_is_to_be_done(imxdi, "main");
> +			return -ENODEV;
> +		}
> +	}
> +
> +	/* disable all sources */
> +	di_write_busy_wait(imxdi, 0x00000000, DTCR);
> +
> +	/* clear the status bits now */
> +	di_write_busy_wait(imxdi, dsr & (DSR_WTD | DSR_ETBD | DSR_ETAD |
> +			DSR_EBD | DSR_SAD | DSR_TTD | DSR_CTD | DSR_VTD |
> +			DSR_MCO | DSR_TCO), DSR);
> +
> +	dsr = __raw_readl(imxdi->ioaddr + DSR);
> +	if ((dsr & ~(DSR_NVF | DSR_SVF | DSR_WBF | DSR_WNF |
> +			DSR_WCF | DSR_WEF)) != 0)
> +		dev_warn(&imxdi->pdev->dev,
> +			"There are still some sources of pain in DSR: %08x!\n",
> +			dsr & ~(DSR_NVF | DSR_SVF | DSR_WBF | DSR_WNF |
> +					DSR_WCF | DSR_WEF));
> +
> +	/*
> +	 * now we are trying to clear the "Security-violation flag" to
> +	 * get the DryIce out of this state
> +	 */
> +	di_write_busy_wait(imxdi, DSR_SVF, DSR);
> +
> +	/* success? */
> +	dsr = __raw_readl(imxdi->ioaddr + DSR);
> +	if (dsr & DSR_SVF) {
> +		dev_crit(&imxdi->pdev->dev,
> +			"Cannot clear the security violation flag. We are ending up in an endless loop!\n");
> +		/* last resourt */
                 resort ^
> +		di_what_is_to_be_done(imxdi, "battery");
> +		return -ENODEV;
> +	}
> +
> +	/*
> +	 * now we have left the "FAILURE STATE" and ending up in the
> +	 * "NON-VALID STATE" time to recover everything
> +	 */
> +	return di_handle_invalid_state(imxdi, dsr);
> +}
> +
> +static int di_handle_state(struct imxdi_dev *imxdi)
> +{
> +	int rc;
> +	u32 dsr;
> +
> +	dsr = __raw_readl(imxdi->ioaddr + DSR);
> +
> +	switch (dsr & (DSR_NVF | DSR_SVF)) {
> +	case DSR_NVF:
> +		dev_warn(&imxdi->pdev->dev, "Invalid stated unit detected\n");
> +		rc = di_handle_invalid_state(imxdi, dsr);
> +		break;
> +	case DSR_SVF:
> +		dev_warn(&imxdi->pdev->dev, "Failure stated unit detected\n");
> +		rc = di_handle_failure_state(imxdi, dsr);
> +		break;
> +	case DSR_NVF | DSR_SVF:
> +		dev_warn(&imxdi->pdev->dev,
> +				"Failure+Invalid stated unit detected\n");
> +		rc = di_handle_invalid_and_failure_state(imxdi, dsr);
> +		break;
> +	default:
> +		dev_notice(&imxdi->pdev->dev, "Unlocked unit detected\n");
> +		rc = di_handle_valid_state(imxdi, dsr);
> +	}
> +
> +	return rc;
> +}
> +
> +
Unnecessary blank line

>  /*
>   * enable a dryice interrupt
>   */
> @@ -491,6 +781,11 @@ static int __init dryice_rtc_probe(struct platform_device *pdev)
>  	/* mask all interrupts */
>  	__raw_writel(0, imxdi->ioaddr + DIER);
>  
> +	rc = di_handle_state(imxdi);
> +	if (rc != 0)
> +		goto err;
> +
> +
Unnecessary blank line

>  	rc = devm_request_irq(&pdev->dev, imxdi->irq, dryice_norm_irq,
>  			IRQF_SHARED, pdev->name, imxdi);
>  	if (rc) {
> @@ -498,44 +793,6 @@ static int __init dryice_rtc_probe(struct platform_device *pdev)
>  		goto err;
>  	}
>  
> -	/* put dryice into valid state */
> -	if (__raw_readl(imxdi->ioaddr + DSR) & DSR_NVF) {
> -		rc = di_write_wait(imxdi, DSR_NVF | DSR_SVF, DSR);

Multiple writes have switched from di_write_wait() which is checking
for a write error to di_write_busy_wait() which is not doing that check
is waiting 200us enough to ensure that the write has been done?

> -		if (rc)
> -			goto err;
> -	}
> -
> -	/* initialize alarm */
> -	rc = di_write_wait(imxdi, DCAMR_UNSET, DCAMR);
> -	if (rc)
> -		goto err;
> -	rc = di_write_wait(imxdi, 0, DCALR);
> -	if (rc)
> -		goto err;
> -
> -	/* clear alarm flag */
> -	if (__raw_readl(imxdi->ioaddr + DSR) & DSR_CAF) {
> -		rc = di_write_wait(imxdi, DSR_CAF, DSR);
> -		if (rc)
> -			goto err;
> -	}
> -
> -	/* the timer won't count if it has never been written to */
> -	if (__raw_readl(imxdi->ioaddr + DTCMR) == 0) {
> -		rc = di_write_wait(imxdi, 0, DTCMR);
> -		if (rc)
> -			goto err;
> -	}
> -
> -	/* start keeping time */
> -	if (!(__raw_readl(imxdi->ioaddr + DCR) & DCR_TCE)) {
> -		rc = di_write_wait(imxdi,
> -				__raw_readl(imxdi->ioaddr + DCR) | DCR_TCE,
> -				DCR);
> -		if (rc)
> -			goto err;
> -	}
> -
>  	platform_set_drvdata(pdev, imxdi);
>  	imxdi->rtc = devm_rtc_device_register(&pdev->dev, pdev->name,
>  				  &dryice_rtc_ops, THIS_MODULE);
> -- 
> 2.1.4
> 

-- 
Alexandre Belloni, Free Electrons
Embedded Linux, Kernel and Android engineering
http://free-electrons.com