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Message-ID:
<PH0PR18MB500275B3BB5FBBBAB15E533ACE6F2@PH0PR18MB5002.namprd18.prod.outlook.com>
Date: Fri, 12 Jan 2024 17:04:39 +0000
From: Linu Cherian <lcherian@...vell.com>
To: Suzuki K Poulose <suzuki.poulose@....com>,
"mike.leach@...aro.org"
<mike.leach@...aro.org>,
"james.clark@....com" <james.clark@....com>,
"leo.yan@...aro.org" <leo.yan@...aro.org>
CC: "linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
"coresight@...ts.linaro.org"
<coresight@...ts.linaro.org>,
"linux-kernel@...r.kernel.org"
<linux-kernel@...r.kernel.org>,
"robh+dt@...nel.org" <robh+dt@...nel.org>,
"krzysztof.kozlowski+dt@...aro.org" <krzysztof.kozlowski+dt@...aro.org>,
"conor+dt@...nel.org" <conor+dt@...nel.org>,
"devicetree@...r.kernel.org"
<devicetree@...r.kernel.org>,
Sunil Kovvuri Goutham <sgoutham@...vell.com>,
George Cherian <gcherian@...vell.com>,
Anil Kumar Reddy H
<areddy3@...vell.com>,
Tanmay Jagdale <tanmay@...vell.com>
Subject: RE: [EXT] Re: [PATCH v6 5/7] coresight: tmc: Add support for reading
tracedata from previous boot
Hi Suzuki,
> -----Original Message-----
> From: Suzuki K Poulose <suzuki.poulose@....com>
> Sent: Tuesday, January 9, 2024 4:22 PM
> To: Linu Cherian <lcherian@...vell.com>; mike.leach@...aro.org;
> james.clark@....com; leo.yan@...aro.org
> Cc: linux-arm-kernel@...ts.infradead.org; coresight@...ts.linaro.org; linux-
> kernel@...r.kernel.org; robh+dt@...nel.org;
> krzysztof.kozlowski+dt@...aro.org; conor+dt@...nel.org;
> devicetree@...r.kernel.org; Sunil Kovvuri Goutham
> <sgoutham@...vell.com>; George Cherian <gcherian@...vell.com>; Anil
> Kumar Reddy H <areddy3@...vell.com>; Tanmay Jagdale
> <tanmay@...vell.com>
> Subject: [EXT] Re: [PATCH v6 5/7] coresight: tmc: Add support for reading
> tracedata from previous boot
>
> External Email
>
> ----------------------------------------------------------------------
> Hi
>
> On 05/01/2024 05:58, Linu Cherian wrote:
> > * Introduce a new mode CS_MODE_READ_PREVBOOT for reading
> tracedata
> > captured in previous boot.
> >
> > * Add special handlers for preparing ETR/ETF for this special mode
> >
> > * User can read the trace data as below
> >
> > For example, for reading trace data from tmc_etf sink
> >
> > 1. cd /sys/bus/coresight/devices/tmc_etfXX/
> >
> > 2. Change mode to READ_PREVBOOT
> >
> > #echo 1 > read_prevboot
>
> I do not like this "new mode" just for reading the crash trace.
> We are in the crash kernel when we have trace metadata available. Could we
> not simply expose this via /dev/tmc_xxx. We can certainly figure this out if
> we are in a crashkernel or not and the trace metadata is valid.
> Also, we should wipe out the trace data/metadata on a normal boot or after
> the crashkernel captures the data.
Somehow couldn’t get the intention behind wiping the tracedata/metadata after retrieval OR its just enough to add a provision to the user for wiping it. Can you please clarify.
We don't expect the user to do tracing in
> the crashkernel, even if the user does it, it is upto the user to overwrite the
> trace. We could even expose a different file for the crash trace/metadata
> (say /dev/tmc_xxx_crash).
>
> But please do not bloat the existing sysfs interface.
>
Since we intend to support the watchdog case as well, we cannot restrict reading the tracedata only from the crashdump kernel. In that regard, using a separate file /dev/tmc_xxx_crash looks better and cleaner option to me.
> Suzuki
>
> >
> > 3. Dump trace buffer data to a file,
> >
> > #dd if=/dev/tmc_etfXX of=~/cstrace.bin
> >
> > 4. Reset back to normal mode
> >
> > #echo 0 > read_prevboot
> >
> > Signed-off-by: Anil Kumar Reddy <areddy3@...vell.com>
> > Signed-off-by: Tanmay Jagdale <tanmay@...vell.com>
> > Signed-off-by: Linu Cherian <lcherian@...vell.com>
> > ---
> > Changelog from v5:
> > * Fixed issues reported by CONFIG_DEBUG_ATOMIC_SLEEP in
> tmc_etr_setup_prevboot_buf
> > and tmc_etb_setup_prevboot_buf
> > - Kmalloc invoked with spinlock taken is now done with GFP_ATOMIC
> > - Removed the requirement for memremap with spinlock taken. This is by
> > making a assumption that the trace buffer address used for capturing
> > trace data during kernel crash/hang would be same as that used
> > for trace data retrieval in the subsequent boot. Added additional
> > verification to ensure this.
> >
> > * Fixed a memory leak in tmc_read_unprepare_etr in READ_PREVBOOT
> mode
> >
> >
> > .../coresight/coresight-etm4x-core.c | 1 +
> > .../hwtracing/coresight/coresight-tmc-core.c | 96 ++++++++++-
> > .../hwtracing/coresight/coresight-tmc-etf.c | 73 +++++++++
> > .../hwtracing/coresight/coresight-tmc-etr.c | 154 +++++++++++++++++-
> > drivers/hwtracing/coresight/coresight-tmc.h | 6 +
> > include/linux/coresight.h | 13 ++
> > 6 files changed, 341 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > index 34aee59dd147..c26b5f72a494 100644
> > --- a/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-etm4x-core.c
> > @@ -1010,6 +1010,7 @@ static void etm4_disable(struct coresight_device
> > *csdev,
> >
> > switch (mode) {
> > case CS_MODE_DISABLED:
> > + case CS_MODE_READ_PREVBOOT:
> > 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 4d7530d6ac91..e6525c3dcf66 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc-core.c
> > +++ b/drivers/hwtracing/coresight/coresight-tmc-core.c
> > @@ -103,6 +103,60 @@ u32 tmc_get_memwidth_mask(struct
> tmc_drvdata *drvdata)
> > return mask;
> > }
> >
> > +int tmc_read_prepare_prevboot(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 prevboot mode preparation */
> > + ret = prevboot_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_prevboot(struct tmc_drvdata *drvdata) {
> > + struct coresight_device *csdev = drvdata->csdev;
> > +
> > + /* Sink specific prevboot mode preparation */
> > + return prevboot_ops(csdev)->unprepare(csdev);
> > +}
> > +
> > static int tmc_read_prepare(struct tmc_drvdata *drvdata)
> > {
> > int ret = 0;
> > @@ -153,6 +207,10 @@ static int tmc_open(struct inode *inode, struct file
> *file)
> > struct tmc_drvdata *drvdata = container_of(file->private_data,
> > struct tmc_drvdata,
> miscdev);
> >
> > + /* Advertise if we are opening with a special mode */
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT)
> > + dev_dbg(&drvdata->csdev->dev, "TMC read mode for
> previous boot\n");
> > +
> > ret = tmc_read_prepare(drvdata);
> > if (ret)
> > return ret;
> > @@ -331,9 +389,44 @@ static ssize_t buffer_size_store(struct device
> > *dev,
> >
> > static DEVICE_ATTR_RW(buffer_size);
> >
> > +static ssize_t read_prevboot_show(struct device *dev,
> > + struct device_attribute *attr, char *buf) {
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > +
> > + return sprintf(buf, "%#x\n", (drvdata->mode ==
> > +CS_MODE_READ_PREVBOOT)); }
> > +
> > +static ssize_t read_prevboot_store(struct device *dev,
> > + struct device_attribute *attr,
> > + const char *buf, size_t size)
> > +{
> > + int ret;
> > + unsigned long val, flags;
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(dev->parent);
> > +
> > + ret = kstrtoul(buf, 0, &val);
> > + if (ret)
> > + return ret;
> > +
> > + spin_lock_irqsave(&drvdata->spinlock, flags);
> > +
> > + if (val && (drvdata->mode == CS_MODE_DISABLED))
> > + drvdata->mode = CS_MODE_READ_PREVBOOT;
> > + else if (!val && (drvdata->mode == CS_MODE_READ_PREVBOOT))
> > + drvdata->mode = CS_MODE_DISABLED;
> > +
> > + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> > +
> > + return size;
> > +}
> > +
> > +static DEVICE_ATTR_RW(read_prevboot);
> > +
> > static struct attribute *coresight_tmc_attrs[] = {
> > &dev_attr_trigger_cntr.attr,
> > &dev_attr_buffer_size.attr,
> > + &dev_attr_read_prevboot.attr,
> > NULL,
> > };
> >
> > @@ -635,7 +728,8 @@ static void tmc_shutdown(struct amba_device
> *adev)
> >
> > spin_lock_irqsave(&drvdata->spinlock, flags);
> >
> > - if (drvdata->mode == CS_MODE_DISABLED)
> > + if (drvdata->mode == CS_MODE_DISABLED ||
> > + drvdata->mode == CS_MODE_READ_PREVBOOT)
> > goto out;
> >
> > if (drvdata->config_type == TMC_CONFIG_TYPE_ETR) diff --git
> > a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > index b53cef7628ff..72c2315f4e23 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> > @@ -648,6 +648,56 @@ static int tmc_panic_sync_etf(struct
> coresight_device *csdev)
> > return 0;
> > }
> >
> > +static int tmc_etb_setup_prevboot_buf(struct tmc_drvdata *drvdata) {
> > + unsigned long size;
> > + struct tmc_crash_metadata *mdata;
> > + struct device *dev = &drvdata->csdev->dev;
> > +
> > + mdata = drvdata->crash_mdata.vaddr;
> > + size = mdata->size << 2;
> > +
> > + /*
> > + * Buffer address given by metadata for retrieval of trace data
> > + * from previous boot is expected to be same as the reserved
> > + * trace buffer memory region provided through DTS
> > + */
> > + if (is_tmc_reserved_region_valid(dev->parent)
> > + && (drvdata->crash_tbuf.paddr == mdata->trc_paddr))
> > + drvdata->buf = drvdata->crash_tbuf.vaddr;
> > + else {
> > + dev_dbg(dev, "Trace buffer address of previous boot
> invalid\n");
> > + return -EINVAL;
> > + }
> > +
> > + drvdata->len = size;
> > + return 0;
> > +}
> > +
> > +static void tmc_etb_free_prevboot_buf(struct tmc_drvdata *drvdata) {
> > + void *buf = drvdata->buf;
> > +
> > + if (!buf)
> > + return;
> > + drvdata->buf = NULL;
> > +}
> > +
> > +static int tmc_etb_prepare_prevboot(struct coresight_device *csdev) {
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(csdev-
> >dev.parent);
> > +
> > + return tmc_etb_setup_prevboot_buf(drvdata);
> > +}
> > +
> > +static int tmc_etb_unprepare_prevboot(struct coresight_device *csdev)
> > +{
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(csdev-
> >dev.parent);
> > +
> > + tmc_etb_free_prevboot_buf(drvdata);
> > + return 0;
> > +}
> > +
> > static const struct coresight_ops_sink tmc_etf_sink_ops = {
> > .enable = tmc_enable_etf_sink,
> > .disable = tmc_disable_etf_sink,
> > @@ -665,6 +715,11 @@ static const struct coresight_ops_panic
> tmc_etf_sync_ops = {
> > .sync = tmc_panic_sync_etf,
> > };
> >
> > +static const struct coresight_ops_prevboot tmc_etf_prevboot_ops = {
> > + .prepare = tmc_etb_prepare_prevboot,
> > + .unprepare = tmc_etb_unprepare_prevboot,
> > +};
> > +
> > const struct coresight_ops tmc_etb_cs_ops = {
> > .sink_ops = &tmc_etf_sink_ops,
> > };
> > @@ -673,6 +728,7 @@ const struct coresight_ops tmc_etf_cs_ops = {
> > .sink_ops = &tmc_etf_sink_ops,
> > .link_ops = &tmc_etf_link_ops,
> > .panic_ops = &tmc_etf_sync_ops,
> > + .prevboot_ops = &tmc_etf_prevboot_ops,
> > };
> >
> > int tmc_read_prepare_etb(struct tmc_drvdata *drvdata) @@ -693,6
> > +749,14 @@ int tmc_read_prepare_etb(struct tmc_drvdata *drvdata)
> > goto out;
> > }
> >
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT) {
> > + ret = tmc_read_prepare_prevboot(drvdata);
> > + if (ret)
> > + goto out;
> > + else
> > + goto mode_valid;
> > + }
> > +
> > /* Don't interfere if operated from Perf */
> > if (drvdata->mode == CS_MODE_PERF) {
> > ret = -EINVAL;
> > @@ -716,6 +780,7 @@ int tmc_read_prepare_etb(struct tmc_drvdata
> *drvdata)
> > __tmc_etb_disable_hw(drvdata);
> > }
> >
> > +mode_valid:
> > drvdata->reading = true;
> > out:
> > spin_unlock_irqrestore(&drvdata->spinlock, flags); @@ -735,8
> > +800,16 @@ int tmc_read_unprepare_etb(struct tmc_drvdata *drvdata)
> > drvdata->config_type != TMC_CONFIG_TYPE_ETF))
> > return -EINVAL;
> >
> > +
> > spin_lock_irqsave(&drvdata->spinlock, flags);
> >
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT) {
> > + tmc_read_unprepare_prevboot(drvdata);
> > + drvdata->reading = false;
> > + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> > + return 0;
> > + }
> > +
> > /* Re-enable the TMC if need be */
> > if (drvdata->mode == CS_MODE_SYSFS) {
> > /* There is no point in reading a TMC in HW FIFO mode */ diff
> > --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > index 23eb35f50571..ab7521bbb2f5 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> > @@ -1166,7 +1166,12 @@ ssize_t tmc_etr_get_sysfs_trace(struct
> tmc_drvdata *drvdata,
> > {
> > s64 offset;
> > ssize_t actual = len;
> > - struct etr_buf *etr_buf = drvdata->sysfs_buf;
> > + struct etr_buf *etr_buf;
> > +
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT)
> > + etr_buf = drvdata->prevboot_buf;
> > + else
> > + etr_buf = drvdata->sysfs_buf;
> >
> > if (pos + actual > etr_buf->len)
> > actual = etr_buf->len - pos;
> > @@ -1873,6 +1878,130 @@ static int tmc_panic_sync_etr(struct
> coresight_device *csdev)
> > return 0;
> > }
> >
> > +static int tmc_etr_setup_prevboot_buf(struct tmc_drvdata *drvdata) {
> > + int rc = 0;
> > + u64 trace_addr;
> > + struct etr_buf *etr_buf;
> > + struct etr_flat_buf *resrv_buf;
> > + struct tmc_crash_metadata *mdata;
> > + struct device *dev = &drvdata->csdev->dev;
> > +
> > + mdata = drvdata->crash_mdata.vaddr;
> > +
> > + etr_buf = kzalloc(sizeof(*etr_buf), GFP_ATOMIC);
> > + if (!etr_buf) {
> > + rc = -ENOMEM;
> > + goto out;
> > + }
> > + etr_buf->size = drvdata->crash_tbuf.size;
> > +
> > + resrv_buf = kzalloc(sizeof(*resrv_buf), GFP_ATOMIC);
> > + if (!resrv_buf) {
> > + rc = -ENOMEM;
> > + goto rmem_err;
> > + }
> > +
> > + /*
> > + * Buffer address given by metadata for retrieval of trace data
> > + * from previous boot is expected to be same as the reserved
> > + * trace buffer memory region provided through DTS
> > + */
> > + if (is_tmc_reserved_region_valid(dev->parent)
> > + && (drvdata->crash_tbuf.paddr == mdata->trc_paddr))
> > + resrv_buf->vaddr = drvdata->crash_tbuf.vaddr;
> > + else {
> > + dev_dbg(dev, "Trace buffer address of previous boot
> invalid\n");
> > + rc = -EINVAL;
> > + goto map_err;
> > + }
> > +
> > + resrv_buf->size = etr_buf->size;
> > + resrv_buf->dev = &drvdata->csdev->dev;
> > + etr_buf->hwaddr = trace_addr;
> > + etr_buf->mode = ETR_MODE_RESRV;
> > + etr_buf->private = resrv_buf;
> > + etr_buf->ops = etr_buf_ops[ETR_MODE_RESRV];
> > +
> > + drvdata->prevboot_buf = etr_buf;
> > +
> > + return 0;
> > +
> > +map_err:
> > + kfree(resrv_buf);
> > +
> > +rmem_err:
> > + kfree(etr_buf);
> > +
> > +out:
> > + return rc;
> > +}
> > +
> > +static int tmc_etr_sync_prevboot_buf(struct tmc_drvdata *drvdata) {
> > + u32 status;
> > + u64 rrp, rwp, dba;
> > + struct tmc_crash_metadata *mdata;
> > + struct etr_buf *etr_buf = drvdata->prevboot_buf;
> > +
> > + mdata = drvdata->crash_mdata.vaddr;
> > +
> > + rrp = mdata->rrp;
> > + rwp = mdata->rwp;
> > + dba = mdata->dba;
> > + status = mdata->sts;
> > +
> > + etr_buf->full = !!(status & TMC_STS_FULL);
> > +
> > + /* Sync the buffer pointers */
> > + etr_buf->offset = rrp - dba;
> > + if (etr_buf->full)
> > + etr_buf->len = etr_buf->size;
> > + else
> > + etr_buf->len = rwp - rrp;
> > +
> > + /* Additional sanity checks for validating metadata */
> > + if ((etr_buf->offset > etr_buf->size) ||
> > + (etr_buf->len > etr_buf->size)) {
> > + dev_dbg(&drvdata->csdev->dev,
> > + "Offset and length invalid in tmc crash metadata\n");
> > + return -EINVAL;
> > + }
> > +
> > + return 0;
> > +}
> > +
> > +static void tmc_etr_free_prevboot_buf(struct tmc_drvdata *drvdata) {
> > + struct etr_buf *etr_buf = drvdata->prevboot_buf;
> > +
> > + if (!etr_buf)
> > + return;
> > + drvdata->prevboot_buf = NULL;
> > +}
> > +
> > +static int tmc_etr_prepare_prevboot(struct coresight_device *csdev) {
> > + int ret = 0;
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(csdev-
> >dev.parent);
> > +
> > + ret = tmc_etr_setup_prevboot_buf(drvdata);
> > + if (ret)
> > + goto out;
> > + ret = tmc_etr_sync_prevboot_buf(drvdata);
> > +
> > +out:
> > + return ret;
> > +}
> > +
> > +static int tmc_etr_unprepare_prevboot(struct coresight_device *csdev)
> > +{
> > + struct tmc_drvdata *drvdata = dev_get_drvdata(csdev-
> >dev.parent);
> > +
> > + tmc_etr_free_prevboot_buf(drvdata);
> > + return 0;
> > +}
> > +
> > static const struct coresight_ops_sink tmc_etr_sink_ops = {
> > .enable = tmc_enable_etr_sink,
> > .disable = tmc_disable_etr_sink,
> > @@ -1885,9 +2014,15 @@ static const struct coresight_ops_panic
> tmc_etr_sync_ops = {
> > .sync = tmc_panic_sync_etr,
> > };
> >
> > +static const struct coresight_ops_prevboot tmc_etr_prevboot_ops = {
> > + .prepare = tmc_etr_prepare_prevboot,
> > + .unprepare = tmc_etr_unprepare_prevboot,
> > +};
> > +
> > const struct coresight_ops tmc_etr_cs_ops = {
> > .sink_ops = &tmc_etr_sink_ops,
> > .panic_ops = &tmc_etr_sync_ops,
> > + .prevboot_ops = &tmc_etr_prevboot_ops,
> > };
> >
> > int tmc_read_prepare_etr(struct tmc_drvdata *drvdata) @@ -1899,12
> > +2034,21 @@ int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
> > if (WARN_ON_ONCE(drvdata->config_type !=
> TMC_CONFIG_TYPE_ETR))
> > return -EINVAL;
> >
> > +
> > spin_lock_irqsave(&drvdata->spinlock, flags);
> > if (drvdata->reading) {
> > ret = -EBUSY;
> > goto out;
> > }
> >
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT) {
> > + ret = tmc_read_prepare_prevboot(drvdata);
> > + if (ret)
> > + goto out;
> > + else
> > + goto mode_valid;
> > + }
> > +
> > /*
> > * We can safely allow reads even if the ETR is operating in PERF
> mode,
> > * since the sysfs session is captured in mode specific data.
> > @@ -1919,6 +2063,7 @@ int tmc_read_prepare_etr(struct tmc_drvdata
> *drvdata)
> > if (drvdata->mode == CS_MODE_SYSFS)
> > __tmc_etr_disable_hw(drvdata);
> >
> > +mode_valid:
> > drvdata->reading = true;
> > out:
> > spin_unlock_irqrestore(&drvdata->spinlock, flags); @@ -1937,6
> > +2082,12 @@ int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
> >
> > spin_lock_irqsave(&drvdata->spinlock, flags);
> >
> > + if (drvdata->mode == CS_MODE_READ_PREVBOOT) {
> > + sysfs_buf = drvdata->prevboot_buf;
> > + tmc_read_unprepare_prevboot(drvdata);
> > + goto out;
> > + }
> > +
> > /* RE-enable the TMC if need be */
> > if (drvdata->mode == CS_MODE_SYSFS) {
> > /*
> > @@ -1954,6 +2105,7 @@ int tmc_read_unprepare_etr(struct tmc_drvdata
> *drvdata)
> > drvdata->sysfs_buf = NULL;
> > }
> >
> > +out:
> > drvdata->reading = false;
> > spin_unlock_irqrestore(&drvdata->spinlock, flags);
> >
> > diff --git a/drivers/hwtracing/coresight/coresight-tmc.h
> > b/drivers/hwtracing/coresight/coresight-tmc.h
> > index 6f13caae6495..6e1e910d5ea4 100644
> > --- a/drivers/hwtracing/coresight/coresight-tmc.h
> > +++ b/drivers/hwtracing/coresight/coresight-tmc.h
> > @@ -216,6 +216,9 @@ struct tmc_resrv_buf {
> > * @idr_mutex: Access serialisation for idr.
> > * @sysfs_buf: SYSFS buffer for ETR.
> > * @perf_buf: PERF buffer for ETR.
> > + * @prevboot_buf: Previous boot buffer for ETR. This is a special purpose
> > + * buffer that is used only for mapping the trace buffer from
> > + * previous boot and not for capturing trace.
> > * @crash_tbuf: Used by ETR as hardware trace buffer and for trace data
> > * retention (after crash) only when ETR_MODE_RESRV buffer
> > * mode is enabled. Used by ETF for trace data retention
> > @@ -247,6 +250,7 @@ struct tmc_drvdata {
> > struct mutex idr_mutex;
> > struct etr_buf *sysfs_buf;
> > struct etr_buf *perf_buf;
> > + struct etr_buf *prevboot_buf;
> > struct tmc_resrv_buf crash_tbuf;
> > struct tmc_resrv_buf crash_mdata;
> > };
> > @@ -298,6 +302,8 @@ void tmc_flush_and_stop(struct tmc_drvdata
> *drvdata);
> > void tmc_enable_hw(struct tmc_drvdata *drvdata);
> > void tmc_disable_hw(struct tmc_drvdata *drvdata);
> > u32 tmc_get_memwidth_mask(struct tmc_drvdata *drvdata);
> > +int tmc_read_prepare_prevboot(struct tmc_drvdata *drvdata); int
> > +tmc_read_unprepare_prevboot(struct tmc_drvdata *drvdata);
> >
> > /* ETB/ETF functions */
> > int tmc_read_prepare_etb(struct tmc_drvdata *drvdata); diff --git
> > a/include/linux/coresight.h b/include/linux/coresight.h index
> > 4fd518738958..9f84decf1d7a 100644
> > --- a/include/linux/coresight.h
> > +++ b/include/linux/coresight.h
> > @@ -294,6 +294,7 @@ enum cs_mode {
> > CS_MODE_DISABLED,
> > CS_MODE_SYSFS,
> > CS_MODE_PERF,
> > + CS_MODE_READ_PREVBOOT, /* Trace data from previous boot */
> > };
> >
> > #define source_ops(csdev) csdev->ops->source_ops
> > @@ -302,6 +303,7 @@ enum cs_mode {
> > #define helper_ops(csdev) csdev->ops->helper_ops
> > #define ect_ops(csdev) csdev->ops->ect_ops
> > #define panic_ops(csdev) csdev->ops->panic_ops
> > +#define prevboot_ops(csdev) csdev->ops->prevboot_ops
> >
> > /**
> > * struct coresight_ops_sink - basic operations for a sink @@
> > -381,12 +383,23 @@ struct coresight_ops_panic {
> > int (*sync)(struct coresight_device *csdev);
> > };
> >
> > +/**
> > + * struct coresight_ops_prevboot - Generic device ops for prevboot
> > +mode
> > + *
> > + * @prepare : Preparation for prevboot mode
> > + */
> > +struct coresight_ops_prevboot {
> > + int (*prepare)(struct coresight_device *csdev);
> > + int (*unprepare)(struct coresight_device *csdev); };
> > +
> > struct coresight_ops {
> > const struct coresight_ops_sink *sink_ops;
> > const struct coresight_ops_link *link_ops;
> > const struct coresight_ops_source *source_ops;
> > const struct coresight_ops_helper *helper_ops;
> > const struct coresight_ops_panic *panic_ops;
> > + const struct coresight_ops_prevboot *prevboot_ops;
> > };
> >
> > #if IS_ENABLED(CONFIG_CORESIGHT)
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