netdev - Re: [PATCH net-next v7 7/9] ethtool: cmis_cdb: Add a layer for supporting CDB commands

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Message-ID: <baf84bde-79d3-4570-a1df-e6adbe14c823@lunn.ch>
Date: Wed, 26 Jun 2024 15:40:08 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Danielle Ratson <danieller@...dia.com>
Cc: "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
	"davem@...emloft.net" <davem@...emloft.net>,
	"edumazet@...gle.com" <edumazet@...gle.com>,
	"kuba@...nel.org" <kuba@...nel.org>,
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	"corbet@....net" <corbet@....net>,
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	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	mlxsw <mlxsw@...dia.com>, Ido Schimmel <idosch@...dia.com>,
	Petr Machata <petrm@...dia.com>
Subject: Re: [PATCH net-next v7 7/9] ethtool: cmis_cdb: Add a layer for
 supporting CDB commands

> > > > +int ethtool_cmis_wait_for_cond(struct net_device *dev, u8 flags, u8 flag,
> > > > +			       u16 max_duration, u32 offset,
> > > > +			       bool (*cond_success)(u8), bool (*cond_fail)(u8),
> > > > +			       u8 *state)
> > > > +{
> > > > +	const struct ethtool_ops *ops = dev->ethtool_ops;
> > > > +	struct ethtool_module_eeprom page_data = {0};
> > > > +	struct cmis_wait_for_cond_rpl rpl = {};
> > > > +	struct netlink_ext_ack extack = {};
> > > > +	unsigned long end;
> > > > +	int err;
> > > > +
> > > > +	if (!(flags & flag))
> > > > +		return 0;
> > > > +
> > > > +	if (max_duration == 0)
> > > > +		max_duration = U16_MAX;
> > > > +
> > > > +	end = jiffies + msecs_to_jiffies(max_duration);
> > > > +	do {
> > > > +		ethtool_cmis_page_init(&page_data, 0, offset, sizeof(rpl));
> > > > +		page_data.data = (u8 *)&rpl;
> > > > +
> > > > +		err = ops->get_module_eeprom_by_page(dev, &page_data,
> > > &extack);
> > > > +		if (err < 0) {
> > > > +			if (extack._msg)
> > > > +				netdev_err(dev, "%s\n", extack._msg);
> > > > +			continue;
> > >
> > > continue here is interested. Say you get -EIO because the module has
> > > been ejected. I would say that is fatal. Won't this spam the logs, as
> > > fast as the I2C bus can fail, without the 20ms sleep, for 65535 jiffies?
> > 
> > If the module is ejected from some reason, it might span the logs I guess.

Please could you test it.

65535 jiffies is i think 655 seconds? That is probably too long to
loop when the module has been ejected. Maybe replace it with HZ?

Maybe netdev_err() should become netdev_dbg()? And please add a 20ms
delay before the continue.

> > > > +		}
> > > > +
> > > > +		if ((*cond_success)(rpl.state))
> > > > +			return 0;
> > > > +
> > > > +		if (*cond_fail && (*cond_fail)(rpl.state))
> > > > +			break;
> > > > +
> > > > +		msleep(20);
> > > > +	} while (time_before(jiffies, end));
> > >
> > > Please could you implement this using iopoll.h. This appears to have
> > > the usual problem. Say msleep(20) actually sleeps a lot longer,
> > > because the system is busy doing other things. time_before(jiffies,
> > > end)) is false, because of the long delay, but in fact the operation
> > > has completed without error. Yet you return EBUSY. iopoll.h gets this
> > > correct, it does one more evaluation of the condition after exiting
> > > the loop to handle this issue.
> > 
> > OK.
> 
> Hi Andrew,
> 
> Therefore, unfortunately in this case I'd rather stay with the origin code.

O.K. Please evaluate the condition again after the while() just so
ETIMEDOUT is not returned in error.

	Andrew