linux-kernel - Re: [PATCH] pci: print out DMA mask info

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Message-ID: <20081012071157.GA20056@colo.lackof.org>
Date:	Sun, 12 Oct 2008 01:11:57 -0600
From:	Grant Grundler <grundler@...isc-linux.org>
To:	Yinghai Lu <yinghai@...nel.org>
Cc:	Grant Grundler <grundler@...isc-linux.org>,
	Matthew Wilcox <matthew@....cx>,
	Jesse Barnes <jbarnes@...tuousgeek.org>,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] pci: print out DMA mask info

On Thu, Oct 09, 2008 at 04:05:57PM -0700, Yinghai Lu wrote:
> Grant Grundler wrote:
> > On Thu, Oct 09, 2008 at 02:51:32PM -0700, Yinghai Lu wrote:
> >> On Thu, Oct 9, 2008 at 2:35 PM, Matthew Wilcox <matthew@....cx> wrote:
> >>> Why's that interesting to the sysadmin of the machine?  To the driver
> >>> writer, certainly.  But what's the use of it to the people using the
> >>> machine?
> > ...
> >> make linux kernel act like black box as other os?
> > 
> > I don't understand your reply.
> > If someone thinks linux is a black box, printing this message won't help them.
> > 
> could find out easily why some driver doesn't set dma mask correctly.
> like why 
> 	qlogic qla2xxx only set consistent to 64bit,
> 	emulex lpfc not set consistent to 64bit

I agree making the information available is a good idea. It's just
not going to help anyone 99% of the time and isn't a requirement for
booting the machine.

> > 
> > "To flag use of bounce buffer or other suboptimal behaviors" could be debated.
> > 
> > 
> > Regarding associating the output with other PCI messages, I'd hope the fact
> > that the /sys entry is in the same directory as other sys files would be
> > enough clue to associate those together. e.g.:
> > grundler <2068>cd /sys/bus/pci/devices/0000\:01\:00.0/
> > grundler <2069>ls
> > broken_parity_status  driver@  irq         resource0   subsystem_device
> > bus@                  enable   local_cpus  resource1   subsystem_vendor
> > class                 i2c-0/   modalias    resource3   uevent
> > config                i2c-1/   power/      rom         vendor
> > device                i2c-2/   resource    subsystem@
> > 
> 
> add dma_mask coherent_dma_mask here?

Yes, if there is no other more obvious place.
It's just a suggestion which I happen to think is better than
adding more boot time messages.

thanks,
grant
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