netdev - Re: [PATCH net-next v3 13/14] net: ethernet: qualcomm: Add PPE debugfs support for PPE counters

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Message-ID: <72171304-9a98-4734-85a3-d1302d053602@lunn.ch>
Date: Fri, 14 Feb 2025 15:02:54 +0100
From: Andrew Lunn <andrew@...n.ch>
To: Jie Luo <quic_luoj@...cinc.com>
Cc: Andrew Lunn <andrew+netdev@...n.ch>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Lei Wei <quic_leiwei@...cinc.com>,
	Suruchi Agarwal <quic_suruchia@...cinc.com>,
	Pavithra R <quic_pavir@...cinc.com>,
	Simon Horman <horms@...nel.org>, Jonathan Corbet <corbet@....net>,
	Kees Cook <kees@...nel.org>,
	"Gustavo A. R. Silva" <gustavoars@...nel.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	linux-arm-msm@...r.kernel.org, netdev@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-hardening@...r.kernel.org,
	quic_kkumarcs@...cinc.com, quic_linchen@...cinc.com,
	srinivas.kandagatla@...aro.org, bartosz.golaszewski@...aro.org,
	john@...ozen.org
Subject: Re: [PATCH net-next v3 13/14] net: ethernet: qualcomm: Add PPE
 debugfs support for PPE counters

> > > +/* The number of packets dropped because of no buffer available, no PPE
> > > + * buffer assigned to these packets.
> > > + */
> > > +static void ppe_port_rx_drop_counter_get(struct ppe_device *ppe_dev,
> > > +					 struct seq_file *seq)
> > > +{
> > > +	u32 reg, drop_cnt = 0;
> > > +	int ret, i, tag = 0;
> > > +
> > > +	PRINT_COUNTER_PREFIX("PRX_DROP_CNT", "SILENT_DROP:");
> > > +	for (i = 0; i < PPE_DROP_CNT_TBL_ENTRIES; i++) {
> > > +		reg = PPE_DROP_CNT_TBL_ADDR + i * PPE_DROP_CNT_TBL_INC;
> > > +		ret = ppe_pkt_cnt_get(ppe_dev, reg, PPE_PKT_CNT_SIZE_1WORD,
> > > +				      &drop_cnt, NULL);
> > > +		if (ret) {
> > > +			seq_printf(seq, "ERROR %d\n", ret);
> > > +			return;
> > > +		}
> > 
> > This is an error getting the value from the hardware? You should not
> > put that into the debugfs itself, you want the read() call to return
> > it.
> > 
> 
> Yes, this error code is returned by regmap read functions in
> ppe_pkt_cnt_get() when the hardware counter read fails. I will
> remove it from debugfs file and instead log the error to the
> console (dev_info).

and return it to user space via the read() call. These functions
normally return the number of bytes put into the buffer. But you can
also return a negative error code which gets passed back to user space
instead.

	Andrew