linux-kernel - Re: [RFC] iommu/vt-d: set default value of INTEL_IOMMU_FLOPPY

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Date:   Wed, 9 Nov 2022 15:05:57 +0800
From:   Baolu Lu <baolu.lu@...ux.intel.com>
To:     Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Cc:     baolu.lu@...ux.intel.com, konrad.wilk@...cle.com,
        harshit.m.mogalapalli@...il.com,
        David Woodhouse <dwmw2@...radead.org>,
        Joerg Roedel <joro@...tes.org>, Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org
Subject: Re: [RFC] iommu/vt-d: set default value of INTEL_IOMMU_FLOPPY_WA to n

On 2022/11/8 20:58, Harshit Mogalapalli wrote:
> It is likely that modern intel motherboard will not ship with a
> floppy connection anymore, so let us disable it by default, as it
> gets turned on when we do a make defconfig.
> 
> Suggested-by: Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>
> Signed-off-by: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
> ---
>   drivers/iommu/intel/Kconfig | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
> index b7dff5092fd2..c783ae85ca9b 100644
> --- a/drivers/iommu/intel/Kconfig
> +++ b/drivers/iommu/intel/Kconfig
> @@ -76,7 +76,7 @@ config INTEL_IOMMU_BROKEN_GFX_WA
>   	  option is removed in the 2.6.32 kernel.
>   
>   config INTEL_IOMMU_FLOPPY_WA
> -	def_bool y
> +	def_bool n
>   	depends on X86
>   	help
>   	  Floppy disk drivers are known to bypass DMA API calls

Nobody selects or depends on this. How about removing this bool? Only
less than 10 lines of code are impacted and are not in any performance
path.

diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index b7dff5092fd2..5e077d1c5f5d 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -75,15 +75,6 @@ config INTEL_IOMMU_BROKEN_GFX_WA
  	  to use physical addresses for DMA, at least until this
  	  option is removed in the 2.6.32 kernel.

-config INTEL_IOMMU_FLOPPY_WA
-	def_bool y
-	depends on X86
-	help
-	  Floppy disk drivers are known to bypass DMA API calls
-	  thereby failing to work when IOMMU is enabled. This
-	  workaround will setup a 1:1 mapping for the first
-	  16MiB to make floppy (an ISA device) work.
-
  config INTEL_IOMMU_SCALABLE_MODE_DEFAULT_ON
  	bool "Enable Intel IOMMU scalable mode by default"
  	default y
diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 48cdcd0a5cf3..22801850f339 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4567,7 +4567,6 @@ static void intel_iommu_get_resv_regions(struct 
device *device,
  	}
  	rcu_read_unlock();

-#ifdef CONFIG_INTEL_IOMMU_FLOPPY_WA
  	if (dev_is_pci(device)) {
  		struct pci_dev *pdev = to_pci_dev(device);

@@ -4579,7 +4578,6 @@ static void intel_iommu_get_resv_regions(struct 
device *device,
  				list_add_tail(&reg->list, head);
  		}
  	}
-#endif /* CONFIG_INTEL_IOMMU_FLOPPY_WA */

  	reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
  				      IOAPIC_RANGE_END - IOAPIC_RANGE_START + 1,

Best regards,
baolu