linux-kernel - Re: [PATCH v4 1/1] xhci: Correctly handle last TRB of isoc TD on Etron xHCI host

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Message-ID: <20250207105124.3cb2e6ae@foxbook>
Date: Fri, 7 Feb 2025 10:51:24 +0100
From: Michał Pecio <michal.pecio@...il.com>
To: Kuangyi Chiang <ki.chiang65@...il.com>
Cc: gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
 linux-usb@...r.kernel.org, mathias.nyman@...el.com, stable@...r.kernel.org
Subject: Re: [PATCH v4 1/1] xhci: Correctly handle last TRB of isoc TD on
 Etron xHCI host

On Fri, 7 Feb 2025 14:59:25 +0800, Kuangyi Chiang wrote:
> >  
> > >       case COMP_STOPPED:
> > > +             /* Think of it as the final event if TD had an error */
> > > +             if (td->error_mid_td)
> > > +                     td->error_mid_td = false;
> > >               sum_trbs_for_length = true;
> > >               break;  
> >
> > What was the reason for this part?  
>
> To prevent the driver from printing the following debug message twice:
>
> "Error mid isoc TD, wait for final completion event"
>
> This can happen if the driver queues a Stop Endpoint command after
> mid isoc TD error occurred, see my debug messages below:

I see. Not sure if it's a big problem, dynamic debug is disabled by
default and anyone using it needs to read the code anyway to understand
what those messages mean. And when you read the code it becomes obvious
why the message can show up twice (or even more, in fact).

I would even say that it is helpful, because it shows that control flow
passes exactly as expected when the Stopped event is handled. And it's
nothing new, this debug code always worked like that on all HCs.

Regards,
Michal