linux-kernel - Re: [PATCH v2 Resent 6/6] i3c: master: svc: fix random hot join failure since timeout errory

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Message-ID: <20231023094853.2510967f@xps-13>
Date:   Mon, 23 Oct 2023 09:48:53 +0200
From:   Miquel Raynal <miquel.raynal@...tlin.com>
To:     Frank Li <Frank.li@....com>
Cc:     alexandre.belloni@...tlin.com, conor.culhane@...vaco.com,
        imx@...ts.linux.dev, joe@...ches.com,
        linux-i3c@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 Resent 6/6] i3c: master: svc: fix random hot join
 failure since timeout errory

Hi Frank,

Frank.li@....com wrote on Fri, 20 Oct 2023 15:58:25 -0400:

> On Fri, Oct 20, 2023 at 07:03:37PM +0200, Miquel Raynal wrote:
> > Hi Frank,
> > 
> > Frank.li@....com wrote on Fri, 20 Oct 2023 11:47:48 -0400:
> >   
> > > On Fri, Oct 20, 2023 at 05:20:06PM +0200, Miquel Raynal wrote:  
> > > > Hi Frank,
> > > > 
> > > > Frank.li@....com wrote on Fri, 20 Oct 2023 10:47:52 -0400:
> > > >     
> > > > > On Fri, Oct 20, 2023 at 04:35:25PM +0200, Miquel Raynal wrote:    
> > > > > > Hi Frank,
> > > > > > 
> > > > > > Frank.li@....com wrote on Fri, 20 Oct 2023 10:18:55 -0400:
> > > > > >       
> > > > > > > On Fri, Oct 20, 2023 at 04:06:45PM +0200, Miquel Raynal wrote:      
> > > > > > > > Hi Frank,
> > > > > > > > 
> > > > > > > > Frank.li@....com wrote on Thu, 19 Oct 2023 11:39:42 -0400:
> > > > > > > >         
> > > > > > > > > On Thu, Oct 19, 2023 at 08:44:52AM +0200, Miquel Raynal wrote:        
> > > > > > > > > > Hi Frank,
> > > > > > > > > > 
> > > > > > > > > > Frank.Li@....com wrote on Wed, 18 Oct 2023 11:59:26 -0400:
> > > > > > > > > >           
> > > > > > > > > > > master side report:
> > > > > > > > > > >   silvaco-i3c-master 44330000.i3c-master: Error condition: MSTATUS 0x020090c7, MERRWARN 0x00100000
> > > > > > > > > > > 
> > > > > > > > > > > BIT 20: TIMEOUT error
> > > > > > > > > > >   The module has stalled too long in a frame. This happens when:
> > > > > > > > > > >   - The TX FIFO or RX FIFO is not handled and the bus is stuck in the
> > > > > > > > > > > middle of a message,
> > > > > > > > > > >   - No STOP was issued and between messages,
> > > > > > > > > > >   - IBI manual is used and no decision was made.          
> > > > > > > > > > 
> > > > > > > > > > I am still not convinced this should be ignored in all cases.
> > > > > > > > > > 
> > > > > > > > > > Case 1 is a problem because the hardware failed somehow.          
> > > > > > > > > 
> > > > > > > > > But so far, no action to handle this case in current code.        
> > > > > > > > 
> > > > > > > > Yes, but if you detect an issue and ignore it, it's not better than
> > > > > > > > reporting it without handling it. Instead of totally ignoring this I
> > > > > > > > would at least write a debug message (identical to what's below) before
> > > > > > > > returning false, even though I am not convinced unconditionally
> > > > > > > > returning false here is wise. If you fail a hardware sequence because
> > > > > > > > you added a printk, it's a problem. Maybe you consider this line as
> > > > > > > > noise, but I believe it's still an error condition. Maybe, however,
> > > > > > > > this bit gets set after the whole sequence, and this is just a "bus
> > > > > > > > is idle" condition. If that's the case, then you need some
> > > > > > > > additional heuristics to properly ignore the bit?
> > > > > > > >         
> > > > > > > 
> > > > > > >                 dev_err(master->dev,                                       
> > > > > > >                         "Error condition: MSTATUS 0x%08x, MERRWARN 0x%08x\n",
> > > > > > >                         mstatus, merrwarn);
> > > > > > > +
> > > > > > > +		/* ignore timeout error */
> > > > > > > +		if (merrwarn & SVC_I3C_MERRWARN_TIMEOUT)
> > > > > > > +			return false;
> > > > > > > +
> > > > > > > 
> > > > > > > Is it okay move SVC_I3C_MERRWARN_TIMEOUT after dev_err?      
> > > > > > 
> > > > > > I think you mentioned earlier that the problem was not the printk but
> > > > > > the return value. So perhaps there is a way to know if the timeout
> > > > > > happened after a transaction and was legitimate or not?      
> > > > > 
> > > > > Error message just annoise user, don't impact function. But return false
> > > > > let IBI thread running to avoid dead lock. 
> > > > >     
> > > > > > 
> > > > > > In any case we should probably lower the log level for this error.      
> > > > > 
> > > > > Only SVC_I3C_MERRWARN_TIMEOUT is warning
> > > > > 
> > > > > Maybe below logic is better
> > > > > 
> > > > > 	if (merrwarn & SVC_I3C_MERRWARN_TIMEOUT) {
> > > > > 		dev_dbg(master->dev, 
> > > > >                         "Error condition: MSTATUS 0x%08x, MERRWARN 0x%08x\n",
> > > > > 			mstatus, merrwarn);
> > > > > 		return false;
> > > > > 	} 
> > > > > 	
> > > > > 	dev_err(master->dev,                                     
> > > > >                 "Error condition: MSTATUS 0x%08x, MERRWARN 0x%08x\n",
> > > > >                  mstatus, merrwarn); 
> > > > > 	....
> > > > >     
> > > > 
> > > > Yes, this looks better but I wonder if we should add an additional
> > > > condition to just return false in this case;     
> > > 
> > > What's additional condition we can check?  
> > 
> > Well, you're the one bothered with an error case which is not a real
> > error. You're saying "this error is never a problem" and I am saying
> > that I believe it is not a problem is your particular case, but in
> > general there might be situations where it *is* a problem. So you need
> > to find proper conditions to check against in order to determine
> > whether this is just an info with no consequence or an error.  
> 
> I checked R** code of this TIMEOUT, which is quite simple, set to 1 if SDA
> is low over 100us if I understand correctly. I also checked, if I add delay
> before emit stop, TIMEOUT will be set. (Read can auto emit stop accoring to
> RDTERM, so just saw TIMEOUT at write transaction).
> 
> TIMEOUT just means condition "I3C bus's SDA low over 100us" happened since
> written 1 to TIMEOUT.
> 
> I think "I3C bus's SDA over 100us" means nothing for linux drivers.
> 
> I think there are NO sitation where it *is* a problem. If it was problem,
> there are NO solution to resolve it at linux driver side. And I think it
> already happen many times silencely. 

Ok then, I'll opt for your last proposal of printing the error message
at the debug loglevel and return false.

Thanks,
Miquèl