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Re: [PATCH 0/5] PCM mmap (temporary) fixes for non-coherent architecture

To: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Subject: Re: [PATCH 0/5] PCM mmap (temporary) fixes for non-coherent architectures
From: Takashi Iwai <tiwai@suse.de>
Date: Fri, 15 Jan 2010 07:43:45 +0100
Cc: Andreas Mohr <andi@lisas.de>, alsa-devel@alsa-project.org, Ralf Baechle <ralf@linux-mips.org>, Wu Zhangjin <wuzhangjin@gmail.com>, Thomas Bogendoerfer <tsbogend@alpha.franken.de>, linux-mips@linux-mips.org, Kumar Gala <galak@gate.crashing.org>, Becky Bruce <beckyb@kernel.crashing.org>
In-reply-to: <1263526082.724.395.camel@pasglop>
References: <1259248388-20095-1-git-send-email-tiwai@suse.de> <20100101193130.GA21510@rhlx01.hs-esslingen.de> <s5haawj7qlv.wl%tiwai@suse.de> <s5hljg24bl7.wl%tiwai@suse.de> <1263526082.724.395.camel@pasglop>
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At Fri, 15 Jan 2010 14:28:02 +1100,
Benjamin Herrenschmidt wrote:
> 
> 
> > A quick patch below (totally untested!) might do that.
> > It's passing the device struct blindly, so not sure whether this would
> > actually work for all dma_alloc_coherent().
> 
> On archs that have dma_ops such as powerpc (but I think x86 too
> nowadays) you cannot use the USB device for dma_* operations. You need
> to get up to the host controller device...

Yep, I don't think this being a proper fix, too.

> It -might- be worth looking at adding code to the USB stack to propagate
> the parent device dma_ops down to USB devices... hard to tell.

Or we may simply need to drop the mmap support on such architectures...


thanks,

Takashi

> 
> Cheers,
> Ben.
> 
> > 
> > Takashi
> > 
> > ---
> > diff --git a/sound/usb/usbaudio.c b/sound/usb/usbaudio.c
> > index 9edef46..6c82026 100644
> > --- a/sound/usb/usbaudio.c
> > +++ b/sound/usb/usbaudio.c
> > @@ -734,7 +734,7 @@ static void snd_complete_sync_urb(struct urb *urb)
> >     }
> >  }
> >  
> > -
> > +#ifdef USBAUDIO_VMALLOC_BUFFER
> >  /* get the physical page pointer at the given offset */
> >  static struct page *snd_pcm_get_vmalloc_page(struct snd_pcm_substream 
> > *subs,
> >                                          unsigned long offset)
> > @@ -769,6 +769,24 @@ static int snd_pcm_free_vmalloc_buffer(struct 
> > snd_pcm_substream *subs)
> >     return 0;
> >  }
> >  
> > +#define preallocate_buffer(chip, pcm, stream) /* NOP */
> > +
> > +#else
> > +#define snd_pcm_get_vmalloc_page   NULL
> > +#define snd_pcm_alloc_vmalloc_buffer       snd_pcm_lib_malloc_pages
> > +#define snd_pcm_free_vmalloc_buffer        snd_pcm_lib_free_pages
> > +
> > +static int preallocate_buffer(struct snd_usb_audio *chip, struct snd_pcm 
> > *pcm,
> > +                         int stream)
> > +{
> > +   struct snd_pcm_substream *subs = pcm->streams[stream].substream;
> > +   if (!subs)
> > +           return 0;
> > +   return snd_pcm_lib_preallocate_pages(subs, SNDRV_DMA_TYPE_DEV,
> > +                                        chip->card->dev,
> > +                                        1024 * 64, 1024 * 1024);
> > +}
> > +#endif
> >  
> >  /*
> >   * unlink active urbs.
> > @@ -2328,6 +2346,7 @@ static int add_audio_endpoint(struct snd_usb_audio 
> > *chip, int stream, struct aud
> >             err = snd_pcm_new_stream(as->pcm, stream, 1);
> >             if (err < 0)
> >                     return err;
> > +           preallocate_buffer(chip, as->pcm, stream);
> >             init_substream(as, stream, fp);
> >             return 0;
> >     }
> > @@ -2356,6 +2375,7 @@ static int add_audio_endpoint(struct snd_usb_audio 
> > *chip, int stream, struct aud
> >     else
> >             strcpy(pcm->name, "USB Audio");
> >  
> > +   preallocate_buffer(chip, pcm, stream);
> >     init_substream(as, stream, fp);
> >  
> >     list_add(&as->list, &chip->pcm_list);
> 
> 

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