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

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Date:   Mon, 17 Apr 2023 08:12:36 +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 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?

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