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Re: SB16 build error.

To: Ralf Baechle <ralf@linux-mips.org>
Subject: Re: SB16 build error.
From: Takashi Iwai <tiwai@suse.de>
Date: Thu, 30 Jun 2011 14:38:20 +0200
Cc: Jaroslav Kysela <perex@perex.cz>, alsa-devel@alsa-project.org, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, florian@linux-mips.org, Florian Fainelli <florian@openwrt.org>, linux-arch@vger.kernel.org, Richard Henderson <rth@twiddle.net>, Ivan Kokshaysky <ink@jurassic.park.msu.ru>, Matt Turner <mattst88@gmail.com>, Benjamin Herrenschmidt <benh@kernel.crashing.org>, Paul Mackerras <paulus@samba.org>, "David S. Miller" <davem@davemloft.net>, sparclinux@vger.kernel.org
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At Thu, 30 Jun 2011 13:32:12 +0100,
Ralf Baechle wrote:
> 
> On Thu, Jun 30, 2011 at 01:28:03PM +0200, Takashi Iwai wrote:
> 
> > > > I have no idea how big the soundblaster microcode being loaded actually 
> > > > is,
> > > > that is if the reduced size of 0x1f00 will be sufficient.
> > > 
> > > The files found in /lib/firmware/sb16 are all under 2kB, thus likely
> > > sufficient.
> > 
> > Too shortly answered.  It turned out that some CSP codes (like Qsound)
> > can be above that size, it's almost 12kB.  So the size in the original
> > code is really the necessary requirement, and the patch breaks for
> > such a case.
> > 
> > An ugly workaround would be to fake the ioctl size.  But this is
> > certainly to be avoided, since it has been broken on the specific
> > platforms for ages, thus breaking for them would be mostly harmless,
> > too.
> > 
> > > > Aside of that I
> > > > don't see a problem - I don't see how the old ioctl can possibly have 
> > > > been
> > > > used before so there isn't a compatibility problem.
> > > > 
> > > > Or you could entirely sidestep the problem and use request_firmware() 
> > > > but
> > > > I guess that's more effort than you want to invest.
> > > 
> > > Yeah, that's another option I thought of.  But it's too intrusive for
> > > 3.0-rc6, so I'd like waive it for 3.1.
> > 
> > Actually the request_firmware() was implemented for some auto-loadable
> > CSP codes.  Others need the manual loading, so it is via ioctl.  It
> > can be converted, but I don't think it makes sense for such old
> > stuff.  After all, it still works with x86-ISA as is.
> 
> In userland an empty definition will be used for _IOC_TYPECHECK so there
> won't be an error.  So userland already is already using the existing
> value for SNDRV_SB_CSP_IOCTL_LOAD_CODE ...

Right.  It has an invalid direction (3), but apps won't care such
details anyway.

> With a crude hack like
> 
> #define SNDRV_SB_CSP_IOCTL_LOAD_CODE                          \
>       _IOC(_IOC_WRITE,'H', 0x11, sizeof(struct snd_sb_csp_microcode))
> 
> error checking can be bypassed and all will be fine as long as the
> resulting value doesn't result in in a a duplicate case value - which it
> doesn't, at least not in my testing.
> 
> Should work but isn't nice.

Indeed.  But which is uglier is hard to answer :)

If you are fine with the hacked ioctl number above, I can put it
with some comments.  This won't break anything, at least.


thanks,

Takashi

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