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

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Date:	Thu, 18 Oct 2012 17:11:04 +0300
From:	Andy Shevchenko <andy.shevchenko@...il.com>
To:	balbi@...com
Cc:	Andy Shevchenko <andriy.shevchenko@...ux.intel.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

On Thu, Oct 18, 2012 at 4:59 PM, Felipe Balbi <balbi@...com> wrote:
> 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.

I will do separate patch for this. If Viresh and/or Vinoud is okay
with it, user will see fat message.

-- 
With Best Regards,
Andy Shevchenko
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