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

Miquel Raynal
2023-10-23T07:49:08Z

Hi Frank,

Frank.li@nxp.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@nxp.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@nxp.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@nxp.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@nxp.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@nxp.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