Hi,

On Tue, 1 Mar 2022 at 11:42, Jinlong Mao quic_jinlmao@quicinc.com wrote:

On 2/28/2022 10:51 PM, Suzuki K Poulose wrote:

Hi Jinlong

On 28/02/2022 13:31, Mao Jinlong wrote:

From: Mao Jinlong jinlmao@qti.qualcomm.com

It is possible that when device probe, its child device is not probed. Then it will fail when add sysfs connection for the device. Make device defer probe when the child device is not probed.

Please could you a bit a more specific on the exact issue ? I don't see a problem with probe deferral right now, with coresight/next.

For e.g.,

root@juno-server:~# lsmod Module Size Used by coresight 73728 0 root@juno-server:~# ls /sys/bus/coresight/devices/ root@juno-server:~# modprobe coresight-etm4x root@juno-server:~# lsmod Module Size Used by coresight_etm4x 81920 0 coresight 73728 1 coresight_etm4x root@juno-server:~# ls /sys/bus/coresight/devices/ etm0 etm1

-- Note etm2-etm5 doesn't appear --

root@juno-server:~# modprobe coresight-funnel root@juno-server:~# lsmod Module Size Used by coresight_funnel 20480 0 coresight_etm4x 81920 0 coresight 73728 2 coresight_etm4x,coresight_funnel root@juno-server:~# ls /sys/bus/coresight/devices/ etm0 etm1

-- Still don't appear ---

root@juno-server:~# modprobe coresight-replicator root@juno-server:~# ls /sys/bus/coresight/devices/ etm0 etm1 root@juno-server:~# modprobe coresight-tmc

-- At this stage, the devices automatically get probed and appear -- root@juno-server:~# ls /sys/bus/coresight/devices/ etm0 etm1 etm2 etm3 etm4 etm5 funnel0 funnel1 funnel2 tmc_etf0 tmc_etr0

root@juno-server:~# lsmod Module Size Used by coresight_tmc 40960 0 coresight_replicator 20480 0 coresight_funnel 20480 0 coresight_etm4x 81920 0 coresight 73728 4 coresight_tmc,coresight_etm4x,coresight_replicator,coresight_funnel

So, my question is, what is this patch trying to solve ?

Cheers Suzuki

Hi Suzuki,

This issue happens when race condition happens. The condition is that the device and its child_device's probe happens at the same time.

For example: device0 and its child device device1. Both of them are calling coresight_register function. device0 is calling coresight_fixup_device_conns. device1 is waiting for device0 to release the coresight_mutex. Because device1's csdev node is allocated, coresight_make_links will be called for device0. Then in coresight_add_sysfs_link, has_conns_grp is true for device0, but has_conns_grp is false for device1 as has_conns_grp is set to true in coresight_create_conns_sysfs_group . The probe of device0 will fail for at this condition.

struct coresight_device *coresight_register(struct coresight_desc *desc) { ......... mutex_lock(&coresight_mutex);

ret = coresight_create_conns_sysfs_group(csdev);
if (!ret)
    ret = coresight_fixup_device_conns(csdev);
if (!ret)
    ret = coresight_fixup_orphan_conns(csdev);
if (!ret && cti_assoc_ops && cti_assoc_ops->add)
    cti_assoc_ops->add(csdev);

mutex_unlock(&coresight_mutex);

.........

}

static int coresight_fixup_device_conns(struct coresight_device *csdev) { .......... conn->child_dev = coresight_find_csdev_by_fwnode(conn->child_fwnode);

The issue appears to be a constraint hidden in the lower layers of the code. Would a better solution not be to alter the code here:

if (conn->child_dev && conn->child_dev->has_conns_grp) { ... } else { csdev->orphan = true; }

which would mean that the connection attempt would drop through to label the connection as an orphan, to be cleaned up by the child itself when it runs coresight_fixup_orphan_conns()

Regards

Mike

    if (conn->child_dev) {
        ret = coresight_make_links(csdev, conn,

                       conn->child_dev);

..........

}

int coresight_add_sysfs_link(struct coresight_sysfs_link *info) { ................ if (!info->orig->has_conns_grp || !info->target->has_conns_grp) return -EINVAL;

The probe fail issue is reproduced with reboot stress test on our internal device.

With the patch, the probe fail issue is not reproduced.

Thanks

Jinlong Mao

Signed-off-by: Mao Jinlong jinlmao@qti.qualcomm.com

drivers/hwtracing/coresight/coresight-sysfs.c | 4 +++- 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/drivers/hwtracing/coresight/coresight-sysfs.c b/drivers/hwtracing/coresight/coresight-sysfs.c index 34d2a2d31d00..7df9eb59bf2c 100644 --- a/drivers/hwtracing/coresight/coresight-sysfs.c +++ b/drivers/hwtracing/coresight/coresight-sysfs.c @@ -73,8 +73,10 @@ int coresight_add_sysfs_link(struct coresight_sysfs_link *info) if (!info->orig || !info->target || !info->orig_name || !info->target_name) return -EINVAL;

• if (!info->orig->has_conns_grp || !info->target->has_conns_grp)

• if (!info->orig->has_conns_grp) return -EINVAL;
• if (!info->target->has_conns_grp)

•    return -EPROBE_DEFER;
    /* first link orig->target */
  ret = sysfs_add_link_to_group(&info->orig->dev.kobj,