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

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Message-ID: <C825CC85444ED85D+20250905011637.GA1091337@nic-Precision-5820-Tower>
Date: Fri, 5 Sep 2025 09:16:37 +0800
From: Yibo Dong <dong100@...se.com>
To: Andrew Lunn <andrew@...n.ch>
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 02:05:57PM +0200, Andrew Lunn wrote:
> 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
> 

Got it, I will update this.

Thanks for your feedback.