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Date: Wed, 9 Nov 2022 17:46:06 +0530
From: Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
To: Baolu Lu <baolu.lu@...ux.intel.com>
Cc: 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,
Darren Kenny <darren.kenny@...cle.com>,
Harshit Mogalapalli <harshit.m.mogalapalli@...cle.com>
Subject: Re: [RFC] iommu/vt-d: set default value of INTEL_IOMMU_FLOPPY_WA to n
On 09/11/22 12:35 pm, Baolu Lu wrote:
> 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(®->list, head);
> }
> }
> -#endif /* CONFIG_INTEL_IOMMU_FLOPPY_WA */
>
> reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
> IOAPIC_RANGE_END - IOAPIC_RANGE_START + 1,
>
Hi Baolu,
I have a question:
Shouldn't we remove the code between ifdef-endif statements?
I mean something like this:
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..2c416ad3204e 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -4567,20 +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);
-
- if ((pdev->class >> 8) == PCI_CLASS_BRIDGE_ISA) {
- reg = iommu_alloc_resv_region(0, 1UL << 24, prot,
- IOMMU_RESV_DIRECT_RELAXABLE,
- GFP_KERNEL);
- if (reg)
- list_add_tail(®->list, head);
- }
- }
-#endif /* CONFIG_INTEL_IOMMU_FLOPPY_WA */
-
reg = iommu_alloc_resv_region(IOAPIC_RANGE_START,
IOAPIC_RANGE_END -
IOAPIC_RANGE_START + 1,
0, IOMMU_RESV_MSI, GFP_KERNEL);
This code is introduced in Commit d850c2ee5fe2 ("iommu/vt-d: Expose ISA
direct mapping region via iommu_get_resv_regions")
If others don't have an objection I can send a patch with the above diff.
Note: I am unsure about the code internals.
Thanks,
Harshit
> Best regards,
> baolu
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