linux-kernel - Re: [PATCH v2] usb: typec: intel_pmc_mux: Expose IOM port status to debugfs

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Date:   Tue, 18 Apr 2023 15:10:47 +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 v2] usb: typec: intel_pmc_mux: Expose IOM port status to
 debugfs

Hi,

On 4/17/2023 11:42 AM, Greg KH wrote:
> On Mon, Apr 17, 2023 at 11:28:18AM +0530, Rajat Khandelwal wrote:
>> Hi,
>>
>> On 4/15/2023 11:01 AM, Greg KH wrote:
>>> On Fri, Apr 14, 2023 at 01:49:10PM +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>
>>>> ---
>>>>
>>>> v2:
>>>> 1. Remove static declaration of the debugfs root for 'intel_pmc_mux'
>>>> 2. Remove explicitly defined one-liner functions
>>>>
>>>>    drivers/usb/typec/mux/intel_pmc_mux.c | 34 +++++++++++++++++++++++++++
>>>>    1 file changed, 34 insertions(+)
>>>>
>>>> diff --git a/drivers/usb/typec/mux/intel_pmc_mux.c b/drivers/usb/typec/mux/intel_pmc_mux.c
>>>> index 34e4188a40ff..1d43b111781e 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>
>>>> @@ -639,9 +640,34 @@ static int pmc_usb_probe_iom(struct pmc_usb *pmc)
>>>>    	return 0;
>>>>    }
>>>> +static int port_iom_status_show(struct seq_file *s, void *unused)
>>>> +{
>>>> +	struct pmc_usb_port *port = s->private;
>>>> +
>>>> +	update_port_status(port);
>>>> +	seq_printf(s, "0x%08x\n", port->iom_status);
>>>> +
>>>> +	return 0;
>>>> +}
>>>> +DEFINE_SHOW_ATTRIBUTE(port_iom_status);
>>>> +
>>>> +static void pmc_mux_port_debugfs_init(struct pmc_usb_port *port,
>>>> +				      struct dentry *pmc_mux_debugfs_root)
>>>> +{
>>>> +	struct dentry *debugfs_dir;
>>>> +	char name[6];
>>>> +
>>>> +	snprintf(name, sizeof(name), "port%d", port->usb3_port - 1);
>>>> +
>>>> +	debugfs_dir = debugfs_create_dir(name, pmc_mux_debugfs_root);
>>>> +	debugfs_create_file("iom_status", 0400, debugfs_dir, port,
>>>> +			    &port_iom_status_fops);
>>>> +}
>>>> +
>>>>    static int pmc_usb_probe(struct platform_device *pdev)
>>>>    {
>>>>    	struct fwnode_handle *fwnode = NULL;
>>>> +	struct dentry *pmc_mux_debugfs_root;
>>>>    	struct pmc_usb *pmc;
>>>>    	int i = 0;
>>>>    	int ret;
>>>> @@ -674,6 +700,8 @@ static int pmc_usb_probe(struct platform_device *pdev)
>>>>    	if (ret)
>>>>    		return ret;
>>>> +	pmc_mux_debugfs_root = debugfs_create_dir("intel_pmc_mux", NULL);
>>> What happens when you have more than one device in the system at the
>>> same time?
>> I'm sorry I didn't understand the question. We would have separate directories
>> for all the ports which would contain the 'iom_status' file, thus representing
>> status for all the ports individually.
>> Can you rephrase the question since I guess you had something else in mind?
> Can you please show the output of the directory
> /sys/kernel/debug/intel_pmc_mux/ with multiple pmc devices in the system
> at the same time?

Sorry, I don't own a system with multiple PMCs. Anyways, do we even have
a system with such design?

Thanks
Rajat

>
> This code seems to want to create that directory for every platform
> device that matches this signature, so that implies you can not have
> more than one of them at a time, which is not good and an artificial
> restriction you are placing on the driver.
>
> thanks,
>
> greg k-h