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

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Message-ID: <CAKv+Gu9xTbnt+qoDjj3CHMbFTf_TWsF-QdCZnAS3dKZ+EBfOpQ@mail.gmail.com>
Date:   Tue, 18 Oct 2016 13:49:09 +0100
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     Mike Travis <travis@....com>
Cc:     Takashi Iwai <tiwai@...e.de>, alsa-devel@...a-project.org,
        perex@...ex.cz,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ALSA: hda - allow 40 bit DMA mask for NVidia devices

On 18 October 2016 at 13:46, Mike Travis <travis@....com> wrote:
>
> Have you tested this change on a system which has physical
> addressing > 40 bits to insure that addresses > 40 bits are
> not simply truncated to an incorrect (mod 40) address?

The device should never see addresses > 40 bits, given that the DMA
mask is set to 40 bits not 64.

> By not restricting the addresses to 32 bits you are not
> restricting the device to the DMA32 zone.
>
> This is what caused the original panic on UV systems.
>
> Btw, the newest nVidia GPUs have > 40 bits of DMA address bits.
>

Thanks,
Ard.