linux-kernel - Re: [PATCH] dma-debug: New interfaces to debug dma mapping errors

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Date:	Mon, 17 Sep 2012 08:25:16 -0700
From:	Greg KH <greg@...ah.com>
To:	Shuah Khan <shuah.khan@...com>
Cc:	konrad.wilk@...cle.com, joerg.roedel@....com, tglx@...utronix.de,
	mingo@...hat.com, hpa@...or.com, rob@...dley.net,
	akpm@...ux-foundation.org, bhelgaas@...gle.com,
	stern@...land.harvard.edu, devel@...uxdriverproject.org,
	x86@...nel.org, LKML <linux-kernel@...r.kernel.org>,
	linux-doc@...r.kernel.org, shuahkhan@...il.com
Subject: Re: [PATCH] dma-debug: New interfaces to debug dma mapping errors

On Mon, Sep 17, 2012 at 08:45:58AM -0600, Shuah Khan wrote:
> On Sun, 2012-09-16 at 19:07 -0700, Greg KH wrote:
> > On Sun, Sep 16, 2012 at 06:52:51PM -0600, Shuah Khan wrote:
> > > +void debug_dma_dump_map_errors(struct device *dev, int all)
> > > +{
> > > +	if (all) {
> > > +		dev_info(dev,
> > > +			 "DMA-API: DMA map error summary:\n"
> > > +			 "DMA map errors returned = %d\n"
> > > +			 "DMA map errors not checked = %d\n"
> > > +			 "DMA unmap errors = %d\n"
> > > +			 "SWIOTLB overflow triggers = %d\n",
> > > +			 dev->dma_map_errors,
> > > +			 dev->dma_map_errors_not_checked,
> > > +			 dev->dma_unmap_errors,
> > > +			 dev->iotlb_overflow_cnt);
> > > +		return;
> > > +	}
> > > +
> > > +	if (dev->dma_map_errors_not_checked) {
> > > +		dev_err(dev,
> > > +			"DMA-API: Driver failed to check\n"
> > > +			"%d out of a total of %d DMA map errors returned\n"
> > > +			"by DMA mapping interfaces\n",
> > > +			dev->dma_map_errors_not_checked,
> > > +			dev->dma_map_errors);
> > > +	}
> > > +
> > > +	if (dev->dma_unmap_errors) {
> > > +		dev_err(dev,
> > > +			"DMA-API: Driver tried to free invalid\n"
> > > +			"DMA addresses %d times\n",
> > > +			dev->dma_unmap_errors);
> > > +	}
> > > +
> > > +	if (dev->iotlb_overflow_cnt) {
> > > +		dev_err(dev,
> > > +			"DMA-API: SWIOTLB overflow buffer triggered %d times\n",
> > > +			dev->iotlb_overflow_cnt);
> > > +	}
> > > +}
> > > +EXPORT_SYMBOL(debug_dma_dump_map_errors);
> > 
> > Don't use syslog for stuff like this, that's not good.  Why not use
> > debugfs?
> 
> This debug interface debug_dma_dump_map_errors() is enabled only when
> CONFIG_DMA_API_DEBUG is enabled, however I agree that debugfs is a
> better choice than logging to syslog. I created debugfs interfaces for
> these error counts at system level. Are recommending the same approach
> for per device counts as well? 

No, I have no idea about that (but hint, I really don't like adding
stuff to struct device for something like this, especially with a #ifdef
in it, that seems really wrong here.)  All I wanted to point out was
that do not use the syslog for this, use debugfs instead.

greg k-h
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