Message-ID: <20170224190711.GA12355@linaro.org>
Date:   Fri, 24 Feb 2017 12:07:11 -0700
From:   Mathieu Poirier <mathieu.poirier@...aro.org>
To:     Leo Yan <leo.yan@...aro.org>
Cc:     Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, mike.leach@...aro.org
Subject: Re: [PATCH v1 2/2] coresight: add support for debug module

On Thu, Feb 23, 2017 at 09:57:47AM +0800, Leo Yan wrote:
> Coresight includes debug module and usually the module connects with CPU
> debug logic. ARMv8 architecture reference manual (ARM DDI 0487A.k) has
> description for related info in "Part H: External Debug".
> 
> Chapter H7 "The Sample-based Profiling Extension" introduces several
> sampling registers, e.g. we can check program counter value with
> combined CPU exception level, secure state, etc. So this is helpful for
> analysis CPU lockup scenarios, e.g. if one CPU has run into infinite
> loop with IRQ disabled. In this case the CPU cannot switch context and
> handle any interrupt (including IPIs), as the result it cannot handle
> SMP call for stack dump.
> 
> This patch is to enable coresight debug module, so firstly this driver
> is to enable clocks for debug module and this is to ensure the debug
> module can be accessed from program or external debugger. And the driver
> uses sample-based registers for debug purpose, e.g. when system detects
> the CPU lockup and trigger panic, the driver will dump program counter
> and combined context registers (EDCIDSR, EDVIDSR); by parsing context
> registers so can quickly get to know CPU secure state, exception level,
> etc.
> 
> Some of the debug module registers are located in CPU power domain, so
> in the driver it has checked the power state for CPU before accessing
> registers within CPU power domain. For most safe way to use this driver,
> it's suggested to disable CPU low power states, this can simply set
> "nohlt" in kernel command line.
> 
> Signed-off-by: Leo Yan <leo.yan@...aro.org>
> ---
>  drivers/hwtracing/coresight/Kconfig           |  10 +
>  drivers/hwtracing/coresight/Makefile          |   1 +
>  drivers/hwtracing/coresight/coresight-debug.c | 396 ++++++++++++++++++++++++++
>  3 files changed, 407 insertions(+)
>  create mode 100644 drivers/hwtracing/coresight/coresight-debug.c
> 
> diff --git a/drivers/hwtracing/coresight/Kconfig b/drivers/hwtracing/coresight/Kconfig
> index 130cb21..2c8883b 100644
> --- a/drivers/hwtracing/coresight/Kconfig
> +++ b/drivers/hwtracing/coresight/Kconfig
> @@ -89,4 +89,14 @@ config CORESIGHT_STM
>  	  logging useful software events or data coming from various entities
>  	  in the system, possibly running different OSs
>  
> +config CORESIGHT_DEBUG
> +	bool "CoreSight debug driver"
> +	depends on ARM || ARM64
> +	help
> +	  This driver provides support for coresight debugging module. This
> +	  is primarily used to dump sample-based profiling registers for
> +	  panic. By disable CPU low power states (like "nohlt" in kernel
> +	  command line), this is more safe and avoid lockup issue when
> +	  access debug module registers.
> +
>  endif
> diff --git a/drivers/hwtracing/coresight/Makefile b/drivers/hwtracing/coresight/Makefile
> index af480d9..d540d45 100644
> --- a/drivers/hwtracing/coresight/Makefile
> +++ b/drivers/hwtracing/coresight/Makefile
> @@ -16,3 +16,4 @@ obj-$(CONFIG_CORESIGHT_SOURCE_ETM4X) += coresight-etm4x.o \
>  					coresight-etm4x-sysfs.o
>  obj-$(CONFIG_CORESIGHT_QCOM_REPLICATOR) += coresight-replicator-qcom.o
>  obj-$(CONFIG_CORESIGHT_STM) += coresight-stm.o
> +obj-$(CONFIG_CORESIGHT_DEBUG) += coresight-debug.o
> diff --git a/drivers/hwtracing/coresight/coresight-debug.c b/drivers/hwtracing/coresight/coresight-debug.c
> new file mode 100644
> index 0000000..a109fef
> --- /dev/null
> +++ b/drivers/hwtracing/coresight/coresight-debug.c
> @@ -0,0 +1,396 @@
> +/*
> + * Copyright (c) 2017 Linaro Limited. All rights reserved.
> + *
> + * Author: Leo Yan <leo.yan@...aro.org>
> + *
> + * This program is free software; you can redistribute it and/or modify it
> + * under the terms of the GNU General Public License version 2 as published by
> + * the Free Software Foundation.
> + *
> + * This program is distributed in the hope that it will be useful, but WITHOUT
> + * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
> + * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
> + * more details.
> + *
> + * You should have received a copy of the GNU General Public License along with
> + * this program.  If not, see <http://www.gnu.org/licenses/>.
> + *
> + */
> +#include <linux/amba/bus.h>
> +#include <linux/coresight.h>
> +#include <linux/cpu.h>
> +#include <linux/device.h>
> +#include <linux/err.h>
> +#include <linux/init.h>
> +#include <linux/io.h>
> +#include <linux/kernel.h>
> +#include <linux/moduleparam.h>
> +#include <linux/slab.h>
> +#include <linux/smp.h>
> +#include <linux/types.h>
> +#include <linux/uaccess.h>
> +
> +#include "coresight-priv.h"
> +
> +#define EDPCSR				0x0A0
> +#define EDCIDSR				0x0A4
> +#define EDVIDSR				0x0A8
> +#define EDPCSR_HI			0x0AC
> +#define EDOSLAR				0x300
> +#define EDPRSR				0x314
> +#define EDDEVID1			0xFC4
> +#define EDDEVID				0xFC8
> +
> +#define EDPCSR_PROHIBITED		0xFFFFFFFF
> +
> +/* bits definition for EDPCSR */
> +#ifndef CONFIG_64BIT
> +#define EDPCSR_THUMB			BIT(0)
> +#define EDPCSR_ARM_INST_MASK		GENMASK(31, 2)
> +#define EDPCSR_THUMB_INST_MASK		GENMASK(31, 1)
> +#endif
> +
> +/* bits definition for EDPRSR */
> +#define EDPRSR_DLK			BIT(6)
> +#define EDPRSR_PU			BIT(0)
> +
> +/* bits definition for EDVIDSR */
> +#define EDVIDSR_NS			BIT(31)
> +#define EDVIDSR_E2			BIT(30)
> +#define EDVIDSR_E3			BIT(29)
> +#define EDVIDSR_HV			BIT(28)
> +#define EDVIDSR_VMID			GENMASK(7, 0)
> +
> +/* bits definition for EDDEVID1 */
> +#define EDDEVID1_PCSR_OFFSET_MASK	GENMASK(3, 0)
> +#define EDDEVID1_PCSR_OFFSET_INS_SET	(0x0)
> +#define EDDEVID1_PCSR_NO_OFFSET		(0x1)

Hi Leo,

The above #define isn't used in the code - please remove.

> +
> +/* bits definition for EDDEVID */
> +#define EDDEVID_PCSAMPLE_MODE		GENMASK(3, 0)
> +#define EDDEVID_IMPL_NONE		(0x0)
> +#define EDDEVID_IMPL_EDPCSR_EDCIDSR	(0x2)
> +#define EDDEVID_IMPL_FULL		(0x3)
> +
> +struct debug_drvdata {
> +	void __iomem	*base;
> +	struct device	*dev;
> +	int		cpu;
> +	struct clk	*dbg_clk;
> +
> +	bool		edpcsr_present;
> +	bool		edvidsr_present;
> +	bool		pc_has_offset;
> +
> +	u32		eddevid;
> +	u32		eddevid1;
> +
> +	u32		edpcsr;
> +	u32		edpcsr_hi;
> +	u32		edprsr;
> +	u32		edvidsr;
> +	u32		edcidsr;
> +};
> +
> +static int debug_count;

No need to make this global - please move this to debug_probe() 

> +static DEFINE_PER_CPU(struct debug_drvdata *, debug_drvdata);
> +
> +static void debug_os_unlock(struct debug_drvdata *drvdata)
> +{
> +	/* Unlocks the debug registers */
> +	writel_relaxed(0x0, drvdata->base + EDOSLAR);
> +	wmb();
> +}
> +
> +/*
> + * According to ARM DDI 0487A.k, before access external debug
> + * registers should firstly check the access permission; if any
> + * below condition has been met then cannot access debug
> + * registers to avoid lockup issue:
> + *
> + * - CPU power domain is powered off;
> + * - The OS Double Lock is locked;
> + *
> + * By checking EDPRSR can get to know if meet these conditions.
> + */
> +static bool debug_access_permit(struct debug_drvdata *drvdata)

s/debug_access_permit/debug_access_permitted

> +{
> +	/* CPU is powered off */
> +	if (!(drvdata->edprsr & EDPRSR_PU))
> +		return false;
> +
> +	/* The OS Double Lock is locked */
> +	if (drvdata->edprsr & EDPRSR_DLK)
> +		return false;
> +
> +	return true;
> +}
> +
> +static void debug_read_regs(struct debug_drvdata *drvdata)
> +{
> +	drvdata->edprsr = readl_relaxed(drvdata->base + EDPRSR);
> +
> +	if (!debug_access_permit(drvdata))
> +		return;
> +
> +	if (!drvdata->edpcsr_present)
> +		return;
> +
> +	CS_UNLOCK(drvdata->base);
> +
> +	debug_os_unlock(drvdata);
> +
> +	drvdata->edpcsr = readl_relaxed(drvdata->base + EDPCSR);
> +
> +	/*
> +	 * As described in ARM DDI 0487A.k, if the processing
> +	 * element (PE) is in debug state, or sample-based
> +	 * profiling is prohibited, EDPCSR reads as 0xFFFFFFFF;
> +	 * EDCIDSR, EDVIDSR and EDPCSR_HI registers also become
> +	 * UNKNOWN state. So directly bail out for this case.
> +	 */
> +	if (drvdata->edpcsr == EDPCSR_PROHIBITED) {
> +		CS_LOCK(drvdata->base);
> +		return;
> +	}
> +
> +	/*
> +	 * A read of the EDPCSR normally has the side-effect of
> +	 * indirectly writing to EDCIDSR, EDVIDSR and EDPCSR_HI;
> +	 * at this point it's safe to read value from them.
> +	 */
> +	drvdata->edcidsr = readl_relaxed(drvdata->base + EDCIDSR);
> +#ifdef CONFIG_64BIT
> +	drvdata->edpcsr_hi = readl_relaxed(drvdata->base + EDPCSR_HI);
> +#endif
> +
> +	if (drvdata->edvidsr_present)
> +		drvdata->edvidsr = readl_relaxed(drvdata->base + EDVIDSR);
> +
> +	CS_LOCK(drvdata->base);
> +}
> +
> +#ifndef CONFIG_64BIT
> +static bool debug_pc_has_offset(struct debug_drvdata *drvdata)
> +{
> +	u32 pcsr_offset;
> +
> +	pcsr_offset = drvdata->eddevid1 & EDDEVID1_PCSR_OFFSET_MASK;
> +
> +	return (pcsr_offset == EDDEVID1_PCSR_OFFSET_INS_SET);
> +}
> +
> +static unsigned long debug_adjust_pc(struct debug_drvdata *drvdata,
> +				     unsigned long pc)
> +{
> +	unsigned long arm_inst_offset = 0, thumb_inst_offset = 0;
> +
> +	if (debug_pc_has_offset(drvdata)) {
> +		arm_inst_offset = 8;
> +		thumb_inst_offset = 4;
> +	}
> +
> +	/* Handle thumb instruction */
> +	if (pc & EDPCSR_THUMB) {
> +		pc = (pc & EDPCSR_THUMB_INST_MASK) - thumb_inst_offset;
> +		return pc;
> +	}
> +
> +	/*
> +	 * Handle arm instruction offset, if the arm instruction
> +	 * is not 4 byte alignment then it's possible the case
> +	 * for implementation defined; keep original value for this
> +	 * case and print info for notice.
> +	 */
> +	if (pc & BIT(1))
> +		pr_emerg("Instruction offset is implementation defined\n");
> +	else
> +		pc = (pc & EDPCSR_ARM_INST_MASK) - arm_inst_offset;
> +
> +	return pc;
> +}
> +#endif
> +
> +static void debug_dump_regs(struct debug_drvdata *drvdata)
> +{
> +	unsigned long pc;
> +
> +	pr_emerg("\tEDPRSR:  %08x (Power:%s DLK:%s)\n", drvdata->edprsr,
> +		 drvdata->edprsr & EDPRSR_PU ? "On" : "Off",
> +		 drvdata->edprsr & EDPRSR_DLK ? "Lock" : "Unlock");
> +
> +	if (!debug_access_permit(drvdata) || !drvdata->edpcsr_present) {
> +		pr_emerg("No permission to access debug registers!\n");
> +		return;
> +	}
> +
> +	if (drvdata->edpcsr == EDPCSR_PROHIBITED) {
> +		pr_emerg("CPU is in Debug state or profiling is prohibited!\n");
> +		return;
> +	}
> +
> +#ifdef CONFIG_64BIT
> +	pc = (unsigned long)drvdata->edpcsr_hi << 32 |
> +	     (unsigned long)drvdata->edpcsr;
> +#else
> +	pc = debug_adjust_pc(drvdata, (unsigned long)drvdata->edpcsr);
> +#endif
> +
> +	pr_emerg("\tEDPCSR:  [<%p>] %pS\n", (void *)pc, (void *)pc);
> +	pr_emerg("\tEDCIDSR: %08x\n", drvdata->edcidsr);
> +
> +	if (!drvdata->edvidsr_present)
> +		return;
> +
> +	pr_emerg("\tEDVIDSR: %08x (State:%s Mode:%s Width:%s VMID:%x)\n",
> +		 drvdata->edvidsr,
> +		 drvdata->edvidsr & EDVIDSR_NS ? "Non-secure" : "Secure",
> +		 drvdata->edvidsr & EDVIDSR_E3 ? "EL3" :
> +			(drvdata->edvidsr & EDVIDSR_E2 ? "EL2" : "EL1/0"),
> +		 drvdata->edvidsr & EDVIDSR_HV ? "64bits" : "32bits",
> +		 drvdata->edvidsr & (u32)EDVIDSR_VMID);
> +}
> +
> +/*
> + * Dump out information on panic.
> + */
> +static int debug_notifier_call(struct notifier_block *self,
> +			       unsigned long v, void *p)
> +{
> +	int cpu;
> +
> +	pr_emerg("ARM external debug module:\n");
> +
> +	for_each_possible_cpu(cpu) {
> +
> +		if (!per_cpu(debug_drvdata, cpu))
> +			continue;
> +
> +		pr_emerg("CPU[%d]:\n", per_cpu(debug_drvdata, cpu)->cpu);
> +
> +		debug_read_regs(per_cpu(debug_drvdata, cpu));
> +		debug_dump_regs(per_cpu(debug_drvdata, cpu));
> +	}
> +
> +	return 0;
> +}
> +
> +static struct notifier_block debug_notifier = {
> +	.notifier_call = debug_notifier_call,
> +};
> +
> +static void debug_init_arch_data(void *info)
> +{
> +	struct debug_drvdata *drvdata = info;
> +	u32 mode;
> +
> +	CS_UNLOCK(drvdata->base);
> +
> +	debug_os_unlock(drvdata);
> +
> +	/* Read device info */
> +	drvdata->eddevid  = readl_relaxed(drvdata->base + EDDEVID);
> +	drvdata->eddevid1 = readl_relaxed(drvdata->base + EDDEVID1);
> +
> +	/* Parse implementation feature */
> +	mode = drvdata->eddevid & EDDEVID_PCSAMPLE_MODE;
> +	if (mode == EDDEVID_IMPL_FULL) {
> +		drvdata->edpcsr_present  = true;
> +		drvdata->edvidsr_present = true;
> +	} else if (mode == EDDEVID_IMPL_EDPCSR_EDCIDSR) {
> +		drvdata->edpcsr_present  = true;
> +		drvdata->edvidsr_present = false;
> +	} else {
> +		drvdata->edpcsr_present  = false;
> +		drvdata->edvidsr_present = false;
> +	}
> +
> +	CS_LOCK(drvdata->base);
> +}
> +
> +static int debug_probe(struct amba_device *adev, const struct amba_id *id)
> +{
> +	int ret;
> +	void __iomem *base;
> +	struct device *dev = &adev->dev;
> +	struct coresight_platform_data *pdata = NULL;
> +	struct debug_drvdata *drvdata;
> +	struct resource *res = &adev->res;
> +	struct device_node *np = adev->dev.of_node;
> +
> +	drvdata = devm_kzalloc(dev, sizeof(*drvdata), GFP_KERNEL);
> +	if (!drvdata)
> +		return -ENOMEM;
> +
> +	if (np) {
> +		pdata = of_get_coresight_platform_data(dev, np);
> +		if (IS_ERR(pdata))
> +			return PTR_ERR(pdata);
> +		adev->dev.platform_data = pdata;
> +	}

I wonder if dragging a coresight_platform_data is worth it.  From what I see the
only thing it is used for is to retrieve the CPU.  As such I think it is better
get the portion of code in of_get_coresight_platform_data() that deals with the
CPU and create a new function (of_coresight_get_cpu()).  That way you can reuse
it here and in of_get_coresight_platform_data(). 

> +
> +	drvdata->dev = &adev->dev;
> +	drvdata->dbg_clk = devm_clk_get(&adev->dev, "dbg_clk");
> +	if (IS_ERR(drvdata->dbg_clk)) {
> +		dev_err(dev, "debug clock initialization failed.\n");
> +		return PTR_ERR(drvdata->dbg_clk);
> +	}
> +
> +	ret = clk_prepare_enable(drvdata->dbg_clk);
> +	if (ret)
> +		return ret;
> +
> +	dev_set_drvdata(dev, drvdata);
> +
> +	/* Validity for the resource is already checked by the AMBA core */
> +	base = devm_ioremap_resource(dev, res);
> +	if (IS_ERR(base))
> +		return PTR_ERR(base);
> +
> +	drvdata->base = base;
> +	drvdata->cpu = pdata ? pdata->cpu : 0;
> +
> +	get_online_cpus();
> +	per_cpu(debug_drvdata, drvdata->cpu) = drvdata;
> +
> +	if (smp_call_function_single(drvdata->cpu,
> +				debug_init_arch_data, drvdata, 1))
> +		dev_err(dev, "Debug arch init failed\n");
> +
> +	if (!debug_count++)
> +		atomic_notifier_chain_register(&panic_notifier_list,
> +					       &debug_notifier);
> +	put_online_cpus();

There is no need to hold the CPUs in place through the chain registration.  This
should go before the if().

> +
> +	dev_info(dev, "%s initialized\n", (char *)id->data);
        
        fprintf(buffer, (char *)id->data, drvdata->cpu);
        dev_info(dev, "%s initialized\n", buffer);

> +	return 0;
> +}
> +
> +static struct amba_id debug_ids[] = {
> +	{       /* Debug for Cortex-A53 */
> +		.id	= 0x000bbd03,
> +		.mask	= 0x000fffff,
> +		.data	= "debug",
       
                .data   = "Coresight debug-CPU%d",

> +	},
> +	{       /* Debug for Cortex-A57 */
> +		.id	= 0x000bbd07,
> +		.mask	= 0x000fffff,
> +		.data	= "debug",
> +	},
> +	{       /* Debug for Cortex-A72 */
> +		.id	= 0x000bbd08,
> +		.mask	= 0x000fffff,
> +		.data	= "debug",
> +	},
> +	{ 0, 0},
> +};
> +
> +static struct amba_driver debug_driver = {
> +	.drv = {
> +		.name   = "coresight-debug",
> +		.suppress_bind_attrs = true,
> +	},
> +	.probe		= debug_probe,
> +	.id_table	= debug_ids,
> +};
> +builtin_amba_driver(debug_driver);
> -- 
> 2.7.4
> 

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