linux-kernel - Re: [PATCH] ALSA: hda - allow 40 bit DMA mask for NVidia devices

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Date:   Tue, 18 Oct 2016 12:25:26 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     "Ard Biesheuvel" <ard.biesheuvel@...aro.org>
Cc:     <alsa-devel@...a-project.org>, <perex@...ex.cz>,
        <linux-kernel@...r.kernel.org>, <travis@....com>
Subject: Re: [PATCH] ALSA: hda - allow 40 bit DMA mask for NVidia devices

On Mon, 17 Oct 2016 18:23:59 +0200,
Ard Biesheuvel wrote:
> 
> Commit 49d9e77e72cf ("ALSA: hda - Fix system panic when DMA > 40 bits
> for Nvidia audio controllers") simply disabled any DMA exceeding 32
> bits for NVidia devices, even though they are capable of performing
> DMA up to 40 bits. On some architectures (such as arm64), system memory
> is not guaranteed to be 32-bit addressable by PCI devices, and so this
> change prevents NVidia devices from working on platforms such as AMD
> Seattle.
> 
> Since the original commit already mentioned that up to 40 bits of DMA
> is supported, and given that the code has been updated in the meantime
> to support a 40 bit DMA mask on other devices, revert commit 49d9e77e72cf
> and explicitly set the DMA mask to 40 bits for NVidia devices.
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>

Thanks, applied.  Since this seems causing a real problem, I added Cc
to stable.


Takashi


> ---
>  sound/pci/hda/hda_intel.c | 7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/sound/pci/hda/hda_intel.c b/sound/pci/hda/hda_intel.c
> index c3469f756ec2..c64d986009a9 100644
> --- a/sound/pci/hda/hda_intel.c
> +++ b/sound/pci/hda/hda_intel.c
> @@ -341,8 +341,7 @@ enum {
>  
>  /* quirks for Nvidia */
>  #define AZX_DCAPS_PRESET_NVIDIA \
> -	(AZX_DCAPS_NO_MSI | /*AZX_DCAPS_ALIGN_BUFSIZE |*/ \
> -	 AZX_DCAPS_NO_64BIT | AZX_DCAPS_CORBRP_SELF_CLEAR |\
> +	(AZX_DCAPS_NO_MSI | AZX_DCAPS_CORBRP_SELF_CLEAR |\
>  	 AZX_DCAPS_SNOOP_TYPE(NVIDIA))
>  
>  #define AZX_DCAPS_PRESET_CTHDA \
> @@ -1716,6 +1715,10 @@ static int azx_first_init(struct azx *chip)
>  		}
>  	}
>  
> +	/* NVidia hardware normally only supports up to 40 bits of DMA */
> +	if (chip->pci->vendor == PCI_VENDOR_ID_NVIDIA)
> +		dma_bits = 40;
> +
>  	/* disable 64bit DMA address on some devices */
>  	if (chip->driver_caps & AZX_DCAPS_NO_64BIT) {
>  		dev_dbg(card->dev, "Disabling 64bit DMA\n");
> -- 
> 2.7.4
> 
>