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Date: Wed, 9 Nov 2022 21:16:53 +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,
Darren Kenny <darren.kenny@...cle.com>
Subject: Re: [RFC] iommu/vt-d: set default value of INTEL_IOMMU_FLOPPY_WA to n
On 2022/11/9 20:16, Harshit Mogalapalli wrote:
>
>
> 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")
As long as floppy driver exists in the tree, we have to include above
code. Otherwise, floppy drivers don't work. At least we can easily find
drivers/block/floppy.c which is still maintained (check MAINTAINERS).:-)
Best regards,
baolu
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