linux-kernel - Re: [PATCHv2 3/4] dw_dmac: change {dev

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Date:	Thu, 18 Oct 2012 16:59:27 +0300
From:	Felipe Balbi <balbi@...com>
To:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
CC:	<balbi@...com>, Viresh Kumar <viresh.linux@...il.com>,
	Vinod Koul <vinod.koul@...el.com>,
	<linux-kernel@...r.kernel.org>,
	spear-devel <spear-devel@...t.st.com>
Subject: Re: [PATCHv2 3/4] dw_dmac: change {dev_}printk() to corresponding
 macros

Hi,

On Thu, Oct 18, 2012 at 02:09:43PM +0300, Andy Shevchenko wrote:
> On Thu, 2012-10-18 at 13:34 +0300, Felipe Balbi wrote: 
> > On Thu, Oct 18, 2012 at 11:15:31AM +0300, Andy Shevchenko wrote:
> > > On Wed, 2012-10-17 at 16:53 +0300, Felipe Balbi wrote: 
> > > > On Wed, Oct 17, 2012 at 04:36:58PM +0300, Andy Shevchenko wrote:
> > > > > On Wed, 2012-10-17 at 16:09 +0300, Felipe Balbi wrote: 
> 
> > > > > > > diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c
> 
> > > > > > > @@ -492,10 +491,8 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
> > > > > > >  	 * controller flagged an error instead of scribbling over
> > > > > > >  	 * random memory locations.
> > > > > > >  	 */
> > > > > > > -	dev_printk(KERN_CRIT, chan2dev(&dwc->chan),
> > > > > > > -			"Bad descriptor submitted for DMA!\n");
> > > > > > > -	dev_printk(KERN_CRIT, chan2dev(&dwc->chan),
> > > > > > > -			"  cookie: %d\n", bad_desc->txd.cookie);
> > > > > > > +	dev_crit(chan2dev(&dwc->chan), "Bad descriptor submitted for DMA!\n");
> > > > > > > +	dev_crit(chan2dev(&dwc->chan), "  cookie: %d\n", bad_desc->txd.cookie);
> > > > > > 
> > > > > > now this is critical, indeed. I would suggest using dev_WARN_ONCE() so
> > > > > > that it's noisy enough to catch the failing user.
> > > > > To this and upper comment, there is an explanation why it's critical. I
> > > > > guess the WARN_ONCE is not good enough, for example if we have more than
> > > > > one user making such noise.
> > > > 
> > > > then use dev_WARN()
> > > I can't see how dev_WARN could be more useful here than the dev_crit. In
> > > current message we have channel and cookie to link back to the user.
> > > What does WARN add meaningful?
> > 
> > a dump_stack()
> 
> How could it be useful? The dwc_handle_error is called from a tasklet
> that is called from scheduler asynchronously. The tasklet is queued in
> interrupt handler.

even if it's not useful, it's a lot more verbose and more likely to get
user's attention. If someone's passing broken DMA descriptor, it should
be a really big fat warning so we can get user reports early enoough.

Anyway, it's your call, I don't mind really.

-- 
balbi

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