linux-kernel - Re: [PATCH] usb: typec: intel_pmc_mux: Expose IOM port status to debugfs

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Message-ID: <c82c6577-a363-241b-ffd6-f5c4c9ed838d@linux.intel.com>
Date:   Tue, 4 Apr 2023 22:48:38 +0530
From:   Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     heikki.krogerus@...ux.intel.com, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] usb: typec: intel_pmc_mux: Expose IOM port status to
 debugfs

Hi,

On 3/30/2023 4:31 PM, Greg KH wrote:
> On Thu, Mar 30, 2023 at 04:18:21PM +0530, Rajat Khandelwal wrote:
>> IOM status has a crucial role during debugging to check the
>> current state of the type-C port.
>> There are ways to fetch the status, but all those require the
>> IOM port status offset, which could change with platform.
>>
>> Make a debugfs directory for intel_pmc_mux and expose the status
>> under it per port basis.
>>
>> Signed-off-by: Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
>> Reviewed-by: Heikki Krogerus <heikki.krogerus@...ux.intel.com>
>> ---
>>   drivers/usb/typec/mux/intel_pmc_mux.c | 44 +++++++++++++++++++++++++++
>>   1 file changed, 44 insertions(+)
>>
>> diff --git a/drivers/usb/typec/mux/intel_pmc_mux.c b/drivers/usb/typec/mux/intel_pmc_mux.c
>> index 34e4188a40ff..c99d20888f5d 100644
>> --- a/drivers/usb/typec/mux/intel_pmc_mux.c
>> +++ b/drivers/usb/typec/mux/intel_pmc_mux.c
>> @@ -15,6 +15,7 @@
>>   #include <linux/usb/typec_mux.h>
>>   #include <linux/usb/typec_dp.h>
>>   #include <linux/usb/typec_tbt.h>
>> +#include <linux/debugfs.h>
>>   
>>   #include <asm/intel_scu_ipc.h>
>>   
>> @@ -145,6 +146,8 @@ struct pmc_usb {
>>   	u32 iom_port_status_offset;
>>   };
>>   
>> +static struct dentry *pmc_mux_debugfs_root;
> Why not just look up the dentry and delete it when you want it with a
> call to debugfs_lookup_and_remove() instead?  That way you don't have to
> keep it around (hint, pass it back from your call to
> pmc_mux_debugfs_init() or better yet, don't even have a
> pmc_mux_debugfs_init() function as it only contains one line and is
> only called in one place.
>
> This will save you the storage space of this variable if debugfs is not
> enabled in your kernel.  A small amount, yes, but it's nicer, right?

I see. Yes, though a small amount, you're anyways right.

1. Though a single-line function, I explicitly defined it to make it more readable.
ATM, maintaining a small different framework within the file for another function
(debugfs) somehow presents a more 'organized' code to me, if that makes sense? :)

2. About the suggestion of not keeping the debugfs_root static throughout the
execution, I can change it as per your suggestion, but I'd like to keep it this
way, if that's ok? This way, it would fit nice in the future if more variables
are to be added.

Let me know your thoughts.

Thanks
Rajat

>
> thanks,
>
> greg k-h