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 12:40:41 +0200
From:   Greg KH <gregkh@...uxfoundation.org>
To:     Rajat Khandelwal <rajat.khandelwal@...ux.intel.com>
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

On Tue, Apr 18, 2023 at 03:53:46PM +0530, Rajat Khandelwal wrote:
> Hi,
> 
> On 4/18/2023 3:48 PM, Greg KH wrote:
> > On Tue, Apr 18, 2023 at 03:10:47PM +0530, Rajat Khandelwal wrote:
> > > 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?
> > You might tomorrow.  So please don't create problems like this when you
> > do not have to.
> 
> We still didn't arrive on a culminating note. :)
> What do you suggest I could do for now? This would be a useful debug tool
> for us since we deal with it quite often.

Then do it properly please.  Look at the /sys/kernel/debug/usb/
directory for examples, specifically /sys/kernel/debug/xhci/.

> If we don't have anything constraining this for now, can we keep it like
> this?

No.