Re: [PATCH] platform/powernv: Avoid re-registration of imc debugfs directory

[Anju T Sudhakar <anju@linux.vnet.ibm.com>]

Hi,

On 8/21/19 10:16 AM, Oliver O'Halloran wrote:
> On Wed, Aug 21, 2019 at 2:10 PM Anju T Sudhakar <anju@linux.vnet.ibm.com> wrote:
>> export_imc_mode_and_cmd() function which creates the debugfs interface for
>> imc-mode and imc-command, is invoked when each nest pmu units is
>> registered.
>> When the first nest pmu unit is registered, export_imc_mode_and_cmd()
>> creates 'imc' directory under `/debug/powerpc`. In the subsequent
>> invocations debugfs_create_dir() function returns, since the directory
>> already exists.
>>
>> The recent commit <c33d442328f55> (debugfs: make error message a bit more
>> verbose), throws a warning if we try to invoke `debugfs_create_dir()`
>> with an already existing directory name.
>>
>> Address this warning by lookup for an existing 'imc' directory,
>> and do not invoke debugfs_create_dir(), if the debugfs interface for
>> imc already exists.
>>
>> This patch is based on:
>>     https://lists.ozlabs.org/pipermail/linuxppc-dev/2019-July/192979.html
>>
>> Signed-off-by: Anju T Sudhakar <anju@linux.vnet.ibm.com>
>> Tested-by: Nageswara R Sastry <rnsastry@linux.vnet.ibm.com>
>> ---
>>   arch/powerpc/platforms/powernv/opal-imc.c | 13 +++++++++----
>>   1 file changed, 9 insertions(+), 4 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/powernv/opal-imc.c b/arch/powerpc/platforms/powernv/opal-imc.c
>> index e04b20625cb9..fc2f0e60a44d 100644
>> --- a/arch/powerpc/platforms/powernv/opal-imc.c
>> +++ b/arch/powerpc/platforms/powernv/opal-imc.c
>> @@ -55,14 +55,19 @@ static void export_imc_mode_and_cmd(struct device_node *node,
>>          static u64 loc, *imc_mode_addr, *imc_cmd_addr;
>>          char mode[16], cmd[16];
>>          u32 cb_offset;
>> +       struct dentry *dir = NULL;
>>          struct imc_mem_info *ptr = pmu_ptr->mem_info;
>>
>> +
>> +       /* Return, if 'imc' interface already exists */
>> +       dir = debugfs_lookup("imc", powerpc_debugfs_root);
>> +       if (dir) {
>> +               dput(dir);
>> +               return;
>> +       }
>>          imc_debugfs_parent = debugfs_create_dir("imc", powerpc_debugfs_root);
> Is there a reason why we create the debugfs directory here and not in
> opal_imc_counters_probe()? There's logic to remove the debugfs
> directory in _probe() already so it seems like a more natural place to
> it.
>
Good point. But we can only create the parent directory,

i.e 'imc' directory in `_probe()` function and the entries can be

created only here. The reason is, this debugfs entries are only for

IMC nest units. So, to get the imc mode and command values from

the nest memory region we need the relevant offsets from the control 
block structure.

Since imc_get_mem_addr_nest() function reads this address

for each chip, we invoke the function to create the debugfs

entries after this values are populated(i.e export_imc_mode_and_cmd() in 
invoked by

imc_get_mem_addr_nest()).

Also, if we create the parent directory in `_probe()` function,

we need to track whether the entries(i.e imc_cmd and imc_mode) are 
created or not.


Regards,

Anju