[PATCH v2 1/1] iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA

[PATCH v2 1/1] iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA

[Lu Baolu]

Commit 62edf5dc4a524 ("intel-iommu: Restore DMAR_BROKEN_GFX_WA option for
broken graphics drivers") was introduced 24 years ago as a temporary
workaround for graphics drivers that used physical addresses for DMA and
avoided DMA APIs. This workaround was disabled by default.

As 24 years have passed, it is expected that graphics driver developers
have migrated their drivers to use kernel DMA APIs. Therefore, this
workaround is no longer required and could been removed.

The Intel iommu driver also provides a "igfx_off" option to turn off
the DAM translation for the graphic dedicated IOMMU. Hence, there is
really no good reason to keep this config option.

Suggested-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
---
 drivers/iommu/intel/iommu.c |  4 ----
 drivers/iommu/intel/Kconfig | 11 -----------
 2 files changed, 15 deletions(-)

Change log:
v2:
 - Add igfx_off option to commit message and Cc Intel graphic
   maintainers.

v1: https://lore.kernel.org/linux-iommu/20240127064512.16744-1-baolu.lu@linux.intel.com/

diff --git a/drivers/iommu/intel/iommu.c b/drivers/iommu/intel/iommu.c
index 6fb5f6fceea1..fc52fcd786aa 100644
--- a/drivers/iommu/intel/iommu.c
+++ b/drivers/iommu/intel/iommu.c
@@ -2660,10 +2660,6 @@ static int __init init_dmars(void)
 		iommu_set_root_entry(iommu);
 	}
 
-#ifdef CONFIG_INTEL_IOMMU_BROKEN_GFX_WA
-	dmar_map_gfx = 0;
-#endif
-
 	if (!dmar_map_gfx)
 		iommu_identity_mapping |= IDENTMAP_GFX;
 
diff --git a/drivers/iommu/intel/Kconfig b/drivers/iommu/intel/Kconfig
index 012cd2541a68..d2d34eb28d94 100644
--- a/drivers/iommu/intel/Kconfig
+++ b/drivers/iommu/intel/Kconfig
@@ -64,17 +64,6 @@ config INTEL_IOMMU_DEFAULT_ON
 	  one is found. If this option is not selected, DMAR support can
 	  be enabled by passing intel_iommu=on to the kernel.
 
-config INTEL_IOMMU_BROKEN_GFX_WA
-	bool "Workaround broken graphics drivers (going away soon)"
-	depends on BROKEN && X86
-	help
-	  Current Graphics drivers tend to use physical address
-	  for DMA and avoid using DMA APIs. Setting this config
-	  option permits the IOMMU driver to set a unity map for
-	  all the OS-visible memory. Hence the driver can continue
-	  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
-- 
2.34.1

RE: [PATCH v2 1/1] iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA

[Tian, Kevin]

> From: Lu Baolu <baolu.lu@linux.intel.com>
> Sent: Tuesday, January 30, 2024 2:08 PM
> 
> Commit 62edf5dc4a524 ("intel-iommu: Restore DMAR_BROKEN_GFX_WA
> option for
> broken graphics drivers") was introduced 24 years ago as a temporary
> workaround for graphics drivers that used physical addresses for DMA and
> avoided DMA APIs. This workaround was disabled by default.
> 
> As 24 years have passed, it is expected that graphics driver developers
> have migrated their drivers to use kernel DMA APIs. Therefore, this
> workaround is no longer required and could been removed.
> 
> The Intel iommu driver also provides a "igfx_off" option to turn off
> the DAM translation for the graphic dedicated IOMMU. Hence, there is
> really no good reason to keep this config option.
> 

s/DAM/DMA/

Re: [PATCH v2 1/1] iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA

[Baolu Lu]

On 2024/1/30 14:24, Tian, Kevin wrote:
>> From: Lu Baolu <baolu.lu@linux.intel.com>
>> Sent: Tuesday, January 30, 2024 2:08 PM
>>
>> Commit 62edf5dc4a524 ("intel-iommu: Restore DMAR_BROKEN_GFX_WA
>> option for
>> broken graphics drivers") was introduced 24 years ago as a temporary
>> workaround for graphics drivers that used physical addresses for DMA and
>> avoided DMA APIs. This workaround was disabled by default.
>>
>> As 24 years have passed, it is expected that graphics driver developers
>> have migrated their drivers to use kernel DMA APIs. Therefore, this
>> workaround is no longer required and could been removed.
>>
>> The Intel iommu driver also provides a "igfx_off" option to turn off
>> the DAM translation for the graphic dedicated IOMMU. Hence, there is
>> really no good reason to keep this config option.
>>
> 
> s/DAM/DMA/

Fixed. :-)

Best regards,
baolu

Re: [PATCH v2 1/1] iommu/vt-d: Remove INTEL_IOMMU_BROKEN_GFX_WA

[Baolu Lu]

On 1/30/24 2:08 PM, Lu Baolu wrote:
> Commit 62edf5dc4a524 ("intel-iommu: Restore DMAR_BROKEN_GFX_WA option for
> broken graphics drivers") was introduced 24 years ago as a temporary
> workaround for graphics drivers that used physical addresses for DMA and
> avoided DMA APIs. This workaround was disabled by default.
> 
> As 24 years have passed, it is expected that graphics driver developers
> have migrated their drivers to use kernel DMA APIs. Therefore, this
> workaround is no longer required and could been removed.
> 
> The Intel iommu driver also provides a "igfx_off" option to turn off
> the DAM translation for the graphic dedicated IOMMU. Hence, there is
> really no good reason to keep this config option.
> 
> Suggested-by: Kevin Tian<kevin.tian@intel.com>
> Signed-off-by: Lu Baolu<baolu.lu@linux.intel.com>
> Reviewed-by: Kevin Tian<kevin.tian@intel.com>
> ---
>   drivers/iommu/intel/iommu.c |  4 ----
>   drivers/iommu/intel/Kconfig | 11 -----------
>   2 files changed, 15 deletions(-)

I have queued this patch for v6.9.

Best regards,
baolu