Re: Patch "ALSA: ctxfi: Fallback DMA mask to 32bit" has been added to the 4.4-stable tree

[Greg KH <gregkh@linuxfoundation.org>]

On Sat, Mar 11, 2017 at 04:28:53PM +0100, Jiri Slaby wrote:
> On 03/08/2017, 11:27 AM, gregkh@linuxfoundation.org wrote:
> > From 15c75b09f8d190f89ab4db463b87d411ca349dfe Mon Sep 17 00:00:00 2001
> > From: Takashi Iwai <tiwai@suse.de>
> > Date: Tue, 28 Feb 2017 17:16:48 +0100
> > Subject: ALSA: ctxfi: Fallback DMA mask to 32bit
> > 
> > From: Takashi Iwai <tiwai@suse.de>
> > 
> > commit 15c75b09f8d190f89ab4db463b87d411ca349dfe upstream.
> > 
> > Currently ctxfi driver tries to set only the 64bit DMA mask on 64bit
> > architectures, and bails out if it fails.  This causes a problem on
> > some platforms since the 64bit DMA isn't always guaranteed.  We should
> > fall back to the default 32bit DMA when 64bit DMA fails.
> > 
> > Fixes: 6d74b86d3c0f ("ALSA: ctxfi - Allow 64bit DMA")
> > Signed-off-by: Takashi Iwai <tiwai@suse.de>
> > Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
> ...
> > @@ -1904,19 +1898,18 @@ static int hw_card_start(struct hw *hw)
> >  {
> >  	int err;
> >  	struct pci_dev *pci = hw->pci;
> > +	const unsigned int dma_bits = BITS_PER_LONG;
> >  
> >  	err = pci_enable_device(pci);
> >  	if (err < 0)
> >  		return err;
> >  
> >  	/* Set DMA transfer mask */
> > -	if (dma_set_mask(&pci->dev, CT_XFI_DMA_MASK) < 0 ||
> > -	    dma_set_coherent_mask(&pci->dev, CT_XFI_DMA_MASK) < 0) {
> > -		dev_err(hw->card->dev,
> > -			"architecture does not support PCI busmaster DMA with mask 0x%llx\n",
> > -			CT_XFI_DMA_MASK);
> > -		err = -ENXIO;
> > -		goto error1;
> > +	if (dma_set_mask(&pci->dev, DMA_BIT_MASK(dma_bits))) {
> 
> I believe the condition is inverted here.
> 
> > +		dma_set_coherent_mask(&pci->dev, DMA_BIT_MASK(dma_bits));
> > +	} else {
> > +		dma_set_mask(&pci->dev, DMA_BIT_MASK(32));
> > +		dma_set_coherent_mask(&pci->dev, DMA_BIT_MASK(32));

As this matches what is in Linus's tree, that means I didn't mess up the
backport :)

But I don't understand the issue, what is wrong here?  Should it try 32
first?

Takashi, any thoughts?

thanks,

greg k-h