linux-kernel - Re: [PATCH] ALSA: emu10k1: Stop using iommu

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Message-ID: <s5ha6cz7lxt.wl-tiwai@suse.de>
Date:   Tue, 05 Apr 2022 14:29:34 +0200
From:   Takashi Iwai <tiwai@...e.de>
To:     Robin Murphy <robin.murphy@....com>
Cc:     perex@...ex.cz, tiwai@...e.com, iommu@...ts.linux-foundation.org,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ALSA: emu10k1: Stop using iommu_present()

On Tue, 05 Apr 2022 14:13:33 +0200,
Robin Murphy wrote:
> 
> iommu_get_domain_for_dev() is already perfectly happy to return NULL
> if the given device has no IOMMU. Drop the unnecessary check.
> 
> Signed-off-by: Robin Murphy <robin.murphy@....com>

This will change the code behavior.  The current code does nothing if
no IOMMU is found, but after your removal of the check, the code
reaches to emu->iommu_workaround = true incorrectly.


thanks,

Takashi

> ---
>  sound/pci/emu10k1/emu10k1_main.c | 3 ---
>  1 file changed, 3 deletions(-)
> 
> diff --git a/sound/pci/emu10k1/emu10k1_main.c b/sound/pci/emu10k1/emu10k1_main.c
> index 86cc1ca025e4..5ffab343b89c 100644
> --- a/sound/pci/emu10k1/emu10k1_main.c
> +++ b/sound/pci/emu10k1/emu10k1_main.c
> @@ -1751,9 +1751,6 @@ static void snd_emu10k1_detect_iommu(struct snd_emu10k1 *emu)
>  
>  	emu->iommu_workaround = false;
>  
> -	if (!iommu_present(emu->card->dev->bus))
> -		return;
> -
>  	domain = iommu_get_domain_for_dev(emu->card->dev);
>  	if (domain && domain->type == IOMMU_DOMAIN_IDENTITY)
>  		return;
> -- 
> 2.28.0.dirty
>