linux-kernel - Re: [PATCH net-next v10 3/5] net: rnpgbe: Add basic mbx ops support

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Message-ID: <908e4c95-81cb-4a95-9235-2d2c8c80d80c@lunn.ch>
Date: Thu, 4 Sep 2025 14:05:57 +0200
From: Andrew Lunn <andrew@...n.ch>
To: Yibo Dong <dong100@...se.com>
Cc: andrew+netdev@...n.ch, davem@...emloft.net, edumazet@...gle.com,
	kuba@...nel.org, pabeni@...hat.com, horms@...nel.org,
	corbet@....net, gur.stavi@...wei.com, maddy@...ux.ibm.com,
	mpe@...erman.id.au, danishanwar@...com, lee@...ger.us,
	gongfan1@...wei.com, lorenzo@...nel.org, geert+renesas@...der.be,
	Parthiban.Veerasooran@...rochip.com, lukas.bulwahn@...hat.com,
	alexanderduyck@...com, richardcochran@...il.com, kees@...nel.org,
	gustavoars@...nel.org, rdunlap@...radead.org,
	vadim.fedorenko@...ux.dev, netdev@...r.kernel.org,
	linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-hardening@...r.kernel.org
Subject: Re: [PATCH net-next v10 3/5] net: rnpgbe: Add basic mbx ops support

On Thu, Sep 04, 2025 at 11:19:48AM +0800, Yibo Dong wrote:
> On Thu, Sep 04, 2025 at 12:24:17AM +0200, Andrew Lunn wrote:
> > >  struct mucse_mbx_info {
> > > +	struct mucse_mbx_stats stats;
> > > +	u32 timeout;
> > > +	u32 usec_delay;
> > > +	u16 size;
> > > +	u16 fw_req;
> > > +	u16 fw_ack;
> > > +	/* lock for only one use mbx */
> > > +	struct mutex lock;
> > >  	/* fw <--> pf mbx */
> > >  	u32 fw_pf_shm_base;
> > >  	u32 pf2fw_mbox_ctrl;
> > 
> > > +/**
> > > + * mucse_obtain_mbx_lock_pf - Obtain mailbox lock
> > > + * @hw: pointer to the HW structure
> > > + *
> > > + * This function maybe used in an irq handler.
> > > + *
> > > + * Return: 0 if we obtained the mailbox lock or else -EIO
> > > + **/
> > > +static int mucse_obtain_mbx_lock_pf(struct mucse_hw *hw)
> > > +{
> > > +	struct mucse_mbx_info *mbx = &hw->mbx;
> > > +	int try_cnt = 5000;
> > > +	u32 reg;
> > > +
> > > +	reg = PF2FW_MBOX_CTRL(mbx);
> > > +	while (try_cnt-- > 0) {
> > > +		mbx_ctrl_wr32(mbx, reg, MBOX_PF_HOLD);
> > > +		/* force write back before check */
> > > +		wmb();
> > > +		if (mbx_ctrl_rd32(mbx, reg) & MBOX_PF_HOLD)
> > > +			return 0;
> > > +		udelay(100);
> > > +	}
> > > +	return -EIO;
> > > +}
> > 
> > If there is a function which obtains a lock, there is normally a
> > function which releases a lock. But i don't see it.
> > 
> 
> The lock is relased when send MBOX_CTRL_REQ in mucse_write_mbx_pf:
> 
> mbx_ctrl_wr32(mbx, ctrl_reg, MBOX_CTRL_REQ);
> 
> Set MBOX_PF_HOLD(bit3) to hold the lock, clear bit3 to release, and set
> MBOX_CTRL_REQ(bit0) to send the req. req and lock are different bits in
> one register. So we send the req along with releasing lock (set bit0 and
> clear bit3).
> Maybe I should add comment like this?
> 
> /* send the req along with releasing the lock */
> mbx_ctrl_wr32(mbx, ctrl_reg, MBOX_CTRL_REQ);

As i said, functions like this come in pairs. obtain/release,
lock/unlock. When reading code, you want to be able to see both of the
pair in a function, to know the unlock is not missing. The kernel even
has tools which will validate all paths through a function releasing
locks. Often error paths get this wrong.

So please make this a function, give it a name which makes it obvious
it is the opposite of mucse_obtain_mbx_lock_pf().

	Andrew