netdev - Re: [PATCH net-next v4] ptp: ocp: Expose various resources on the timecard.

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Message-ID: <20210805172623.mwyh4wt3gupfiurd@bsd-mbp.dhcp.thefacebook.com>
Date:   Thu, 5 Aug 2021 10:26:23 -0700
From:   Jonathan Lemon <jonathan.lemon@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, richardcochran@...il.com, kernel-team@...com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net-next v4] ptp: ocp: Expose various resources on the
 timecard.

On Thu, Aug 05, 2021 at 06:03:26AM -0700, Jakub Kicinski wrote:
> On Wed, 4 Aug 2021 16:52:23 -0700 Jonathan Lemon wrote:
> > > > +static int
> > > > +ptp_ocp_devlink_info_get(struct devlink *devlink, struct devlink_info_req *req,
> > > > +			 struct netlink_ext_ack *extack)
> > > > +{
> > > > +	struct ptp_ocp *bp = devlink_priv(devlink);
> > > > +	char buf[32];
> > > > +	int err;
> > > > +
> > > > +	err = devlink_info_driver_name_put(req, KBUILD_MODNAME);
> > > > +	if (err)
> > > > +		return err;
> > > > +
> > > > +	if (bp->pending_image) {
> > > > +		err = devlink_info_version_stored_put(req,
> > > > +						      "timecard", "pending");  
> > > 
> > > "pending" is not a version. It seems you're talking to the flash
> > > directly, why not read the version?  
> > 
> > We're not talking to the flash yet.  We're writing a new image, but don't
> > know the image version, since it's not accessible from the FPGA blob.  So
> > since we're don't know what the stored image is until we reboot, I've set
> > it to 'pending' here - aka "pending reboot".  Could also be "unknown".
> 
> Having the driver remember that the device was flashed is not a solid
> indication that the image is actually different. It may be that user
> flashed the same version, driver may get reloaded and lose the
> indication.. Let's not make a precedent for (ab) use of the version
> field to indicate reset required.

I'd like to have some way to remind/tell the user that a reset is required.

Right now, I can only get the running version from the FPGA register, so
after flashing, there's no way for me to know what's on the flash (or if 
the flash write failed).  Setting "pending" or "reboot" works for most
cases - but obviously fails if the driver is reloaded. 

But most users won't do rmmod/insmod, just a reboot.


> > > > +	}
> > > > +
> > > > +	if (bp->image) {
> > > > +		u32 ver = ioread32(&bp->image->version);
> > > > +
> > > > +		if (ver & 0xffff) {
> > > > +			sprintf(buf, "%d", ver);
> > > > +			err = devlink_info_version_running_put(req,
> > > > +							       "timecard",
> > > > +							       buf);
> > > > +		} else {
> > > > +			sprintf(buf, "%d", ver >> 16);
> > > > +			err = devlink_info_version_running_put(req,
> > > > +							       "golden flash",
> > > > +							       buf);  
> > > 
> > > What's the difference between "timecard" and "golden flash"?  
> > 
> > There are two images stored in flash: "golden image", an image that
> > just provides flash functionality, and the actual featured FPGA image.
> > 
> > > Why call firmware for a timecard timecard? We don't call NIC
> > > firmware "NIC".  
> > 
> > I didn't see a standard string to use.  I can call it 'fw.version', just
> > needed to differentiate it between the 'golden flash' loader and actual
> > firmware.
> 
> Is the 'golden flash' a backup in case full featured image does not
> work or 'first stage' image/'loader'? IIUC it's the latter so maybe
> we can just use "loader"? "fw" for the actual image would be better 
> than "fw.version" the entire string is a version after all.

Undetermined.  I believe that /currently/ it is the same image, but
that is just happenstance.  The vendor says the only functionality 
that the golden image guarantees is flashing - the rest of the FPGA
may or may not work.

I'll use "fw" and "loader".


> > > > +static void
> > > > +ptp_ocp_devlink_health_register(struct devlink *devlink)
> > > > +{
> > > > +	struct ptp_ocp *bp = devlink_priv(devlink);
> > > > +	struct devlink_health_reporter *r;
> > > > +
> > > > +	r = devlink_health_reporter_create(devlink, &ptp_ocp_health_ops, 0, bp);
> > > > +	if (IS_ERR(r))
> > > > +		dev_err(&bp->pdev->dev, "Failed to create reporter, err %ld\n",
> > > > +			PTR_ERR(r));
> > > > +	bp->health = r;
> > > > +}  
> > > 
> > > What made you use devlink health here? Why not just print that "No GPS
> > > signal" message to the logs? Devlink health is supposed to give us
> > > meaningful context dumps and remediation, here neither is used.  
> > 
> > The initial idea was to use 'devlink monitor' report the immediate
> > failure of the GNSS signal (rather than going through the kernel logs)
> > The 'devlink health' also keeps a count of how often the GPS signal
> > is lost.
> > 
> > Our application guys decided to use a different monitoring method,
> > so I can rip this out if objectionable. 
> 
> Great, thanks!