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Message-ID: <a676105a-2f38-498b-87cb-94e0c2406408@arm.com>
Date: Wed, 5 Jun 2024 17:09:10 +0100
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Subject: Re: [PATCH v9 5/7] coresight: tmc: Add support for reading crash data
To: Linu Cherian <lcherian@marvell.com>
Cc: linux-arm-kernel@lists.infradead.org, coresight@lists.linaro.org,
 linux-kernel@vger.kernel.org, robh+dt@kernel.org,
 krzysztof.kozlowski+dt@linaro.org, conor+dt@kernel.org,
 devicetree@vger.kernel.org, sgoutham@marvell.com, gcherian@marvell.com,
 Anil Kumar Reddy <areddy3@marvell.com>, Tanmay Jagdale <tanmay@marvell.com>,
 suzuki.poulose@arm.com, mike.leach@linaro.org
References: <20240605081725.622953-1-lcherian@marvell.com>
 <20240605081725.622953-6-lcherian@marvell.com>
Content-Language: en-US
From: James Clark <james.clark@arm.com>
In-Reply-To: <20240605081725.622953-6-lcherian@marvell.com>
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On 05/06/2024 09:17, Linu Cherian wrote:
> * Introduce a new mode CS_MODE_READ_CRASHDATA for reading trace
>   captured in previous crash/watchdog reset.
> 
> * Add special device files for reading ETR/ETF crash data.
> 
> * User can read the crash data as below
> 
>   For example, for reading crash data from tmc_etf sink
> 
>   #dd if=/dev/crash_tmc_etfXX of=~/cstrace.bin
> 
> Signed-off-by: Anil Kumar Reddy <areddy3@marvell.com>
> Signed-off-by: Tanmay Jagdale <tanmay@marvell.com>
> Signed-off-by: Linu Cherian <lcherian@marvell.com>
> ---
> Changelog from v8:
> * Added missing exit path in __tmc_probe
> * Few whitespace fixes and a checkpatch fix.
> 
>  .../coresight/coresight-etm4x-core.c          |   1 +
>  .../hwtracing/coresight/coresight-tmc-core.c  | 150 ++++++++++++++++-
>  .../hwtracing/coresight/coresight-tmc-etf.c   |  72 +++++++++
>  .../hwtracing/coresight/coresight-tmc-etr.c   | 151 +++++++++++++++++-
>  drivers/hwtracing/coresight/coresight-tmc.h   |  11 +-
>  include/linux/coresight.h                     |  13 ++
>  6 files changed, 390 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> index a0bdfabddbc6..7924883476c6 100644
> --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> @@ -1011,6 +1011,7 @@ static void etm4_disable(struct coresight_device *csdev,
>  
>  	switch (mode) {
>  	case CS_MODE_DISABLED:
> +	case CS_MODE_READ_CRASHDATA:
>  		break;
>  	case CS_MODE_SYSFS:
>  		etm4_disable_sysfs(csdev);
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-core.c b/drivers/hwtracing/coresight/coresight-tmc-core.c
> index daad08bc693d..0c145477ba66 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> @@ -106,6 +106,60 @@ u32 tmc_get_memwidth_mask(struct tmc_drvdata *drvdata)
>  	return mask;
>  }
>  
> +int tmc_read_prepare_crashdata(struct tmc_drvdata *drvdata)
> +{
> +	int ret = 0;
> +	struct tmc_crash_metadata *mdata;
> +	struct coresight_device *csdev = drvdata->csdev;
> +
> +	if (!drvdata->crash_mdata.vaddr) {
> +		ret = -ENOMEM;
> +		goto out;
> +	}
> +
> +	mdata = drvdata->crash_mdata.vaddr;
> +	/* Check data integrity of metadata */
> +	if (mdata->crc32_mdata != find_crash_metadata_crc(mdata)) {
> +		dev_dbg(&drvdata->csdev->dev,
> +			"CRC mismatch in tmc crash metadata\n");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +	/* Check data integrity of tracedata */
> +	if (mdata->crc32_tdata != find_crash_tracedata_crc(drvdata, mdata)) {
> +		dev_dbg(&drvdata->csdev->dev,
> +			"CRC mismatch in tmc crash tracedata\n");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +	/* Check for valid metadata */
> +	if (!mdata->valid) {
> +		dev_dbg(&drvdata->csdev->dev,
> +			"Data invalid in tmc crash metadata\n");
> +		ret = -EINVAL;
> +		goto out;
> +	}
> +
> +	/* Sink specific crashdata mode preparation */
> +	ret = crashdata_ops(csdev)->prepare(csdev);
> +	if (ret)
> +		goto out;
> +
> +	if (mdata->sts & 0x1)
> +		coresight_insert_barrier_packet(drvdata->buf);
> +
> +out:
> +	return ret;
> +}
> +
> +int tmc_read_unprepare_crashdata(struct tmc_drvdata *drvdata)
> +{
> +	struct coresight_device *csdev = drvdata->csdev;
> +
> +	/* Sink specific crashdata mode preparation */
> +	return crashdata_ops(csdev)->unprepare(csdev);
> +}
> +
>  static int tmc_read_prepare(struct tmc_drvdata *drvdata)
>  {
>  	int ret = 0;
> @@ -156,6 +210,9 @@ static int tmc_open(struct inode *inode, struct file *file)
>  	struct tmc_drvdata *drvdata = container_of(file->private_data,
>  						   struct tmc_drvdata, miscdev);
>  
> +	if (coresight_get_mode(drvdata->csdev) == CS_MODE_READ_CRASHDATA)
> +		return -EBUSY;
> +
>  	ret = tmc_read_prepare(drvdata);
>  	if (ret)
>  		return ret;
> @@ -180,13 +237,12 @@ static inline ssize_t tmc_get_sysfs_trace(struct tmc_drvdata *drvdata,
>  	return -EINVAL;
>  }
>  
> -static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
> -			loff_t *ppos)
> +static ssize_t tmc_read_common(struct tmc_drvdata *drvdata, char __user *data,
> +			       size_t len, loff_t *ppos)
>  {
>  	char *bufp;
>  	ssize_t actual;
> -	struct tmc_drvdata *drvdata = container_of(file->private_data,
> -						   struct tmc_drvdata, miscdev);
> +
>  	actual = tmc_get_sysfs_trace(drvdata, *ppos, len, &bufp);
>  	if (actual <= 0)
>  		return 0;
> @@ -203,6 +259,15 @@ static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
>  	return actual;
>  }
>  
> +static ssize_t tmc_read(struct file *file, char __user *data, size_t len,
> +			loff_t *ppos)
> +{
> +	struct tmc_drvdata *drvdata = container_of(file->private_data,
> +						   struct tmc_drvdata, miscdev);
> +
> +	return tmc_read_common(drvdata, data, len, ppos);
> +}
> +
>  static int tmc_release(struct inode *inode, struct file *file)
>  {
>  	int ret;
> @@ -225,6 +290,61 @@ static const struct file_operations tmc_fops = {
>  	.llseek		= no_llseek,
>  };
>  
> +static int tmc_crashdata_open(struct inode *inode, struct file *file)
> +{
> +	int ret;
> +	struct tmc_drvdata *drvdata = container_of(file->private_data,
> +						   struct tmc_drvdata,
> +						   crashdev);
> +
> +	if (!coresight_take_mode(drvdata->csdev, CS_MODE_READ_CRASHDATA))
> +		return -EBUSY;
> +
> +	ret = tmc_read_prepare(drvdata);
> +	if (ret) {
> +		coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> +		return ret;
> +	}
> +
> +	nonseekable_open(inode, file);
> +
> +	dev_dbg(&drvdata->csdev->dev, "%s: successfully opened\n", __func__);
> +	return 0;
> +}
> +
> +static ssize_t tmc_crashdata_read(struct file *file, char __user *data,
> +				  size_t len, loff_t *ppos)
> +{
> +	struct tmc_drvdata *drvdata = container_of(file->private_data,
> +						   struct tmc_drvdata,
> +						   crashdev);
> +
> +	return tmc_read_common(drvdata, data, len, ppos);
> +}
> +
> +static int tmc_crashdata_release(struct inode *inode, struct file *file)
> +{
> +	int ret = 0;
> +	struct tmc_drvdata *drvdata = container_of(file->private_data,
> +						   struct tmc_drvdata,
> +						   crashdev);
> +
> +	ret = tmc_read_unprepare(drvdata);
> +
> +	coresight_set_mode(drvdata->csdev, CS_MODE_DISABLED);
> +
> +	dev_dbg(&drvdata->csdev->dev, "%s: released\n", __func__);
> +	return ret;
> +}
> +
> +static const struct file_operations tmc_crashdata_fops = {
> +	.owner		= THIS_MODULE,
> +	.open		= tmc_crashdata_open,
> +	.read		= tmc_crashdata_read,
> +	.release	= tmc_crashdata_release,
> +	.llseek		= no_llseek,
> +};
> +
>  static enum tmc_mem_intf_width tmc_get_memwidth(u32 devid)
>  {
>  	enum tmc_mem_intf_width memwidth;
> @@ -542,6 +662,18 @@ static u32 tmc_etr_get_max_burst_size(struct device *dev)
>  	return burst_size;
>  }
>  
> +static void register_crash_dev_interface(struct tmc_drvdata *drvdata,
> +					 const char *name)
> +{
> +	drvdata->crashdev.name =
> +		devm_kasprintf(&drvdata->csdev->dev, GFP_KERNEL, "%s_%s", "crash", name);
> +	drvdata->crashdev.minor = MISC_DYNAMIC_MINOR;
> +	drvdata->crashdev.fops = &tmc_crashdata_fops;
> +	if (misc_register(&drvdata->crashdev))
> +		dev_dbg(&drvdata->csdev->dev,
> +			"Failed to setup user interface for crashdata\n");
> +}
> +
>  static int __tmc_probe(struct device *dev, struct resource *res)
>  {
>  	int ret = 0;
> @@ -642,8 +774,13 @@ static int __tmc_probe(struct device *dev, struct resource *res)
>  	drvdata->miscdev.minor = MISC_DYNAMIC_MINOR;
>  	drvdata->miscdev.fops = &tmc_fops;
>  	ret = misc_register(&drvdata->miscdev);
> -	if (ret)
> +	if (ret) {
>  		coresight_unregister(drvdata->csdev);
> +		goto out;
> +	}
> +
> +	if (is_tmc_reserved_region_valid(dev))
> +		register_crash_dev_interface(drvdata, desc.name);

I think this would be better if it checked the CRC of the metadata in
the same way it does before reading the file.

Now we have two forms of "region valid", one that's any non-zero value,
and the other "really valid" one. And because we don't check the CRC
here we register a device that can't be used.

I found it a bit confusing because without enabling debug prints I
didn't know why the file couldn't be read. So I wasn't sure if it was
because it wasn't valid or some other reason.

I also wasn't able to get a valid region after booting the crash kernel.
But maybe the memory isn't preserved across the reboot on my Juno, so I
don't think that's necessarily an issue?