Re: [PATCH] coresight: Defer probe when the child dev is not probed

[Suzuki K Poulose <suzuki.poulose@arm.com>]

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

> 
> 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,