Subject: [PATCH] ACPI/IORT: Fix PCI ACS enablement

From: [email-masked] (Lorenzo Pieralisi)
Date: Thu, 28 Sep 2017 16:46:25 +0100

On Sat, Sep 23, 2017 at 10:26:29AM +0800, Zhou Wang wrote:
> On 2017/9/22 17:45, Lorenzo Pieralisi wrote:
> > On Thu, Sep 21, 2017 at 07:32:58PM +0800, Zhou Wang wrote:
> >> On 2017/9/20 1:05, Lorenzo Pieralisi wrote:
> >>> commit f6810c15cf97 ("iommu/arm-smmu: Clean up early-probing
> >>> workarounds") removed kernel code that was allowing to initialize
> >>> and probe the SMMU devices early (ie earlier than PCI devices through
> >>> linker script callback entries) in the boot process because it was not
> >>> needed any longer in that the SMMU devices/drivers now support deferred
> >>> probing.
> >>>
> >>> Since the SMMUs probe routines are also in charge of requesting global
> >>> PCI ACS kernel enablement, commit f6810c15cf97 ("iommu/arm-smmu: Clean
> >>> up early-probing workarounds") also postponed PCI ACS enablement to
> >>> SMMUs devices probe time, which may be too late given that PCI devices
> >>> needs to detect if PCI ACS is enabled to init the respective capability
> >>> through the following call path:
> >>>
> >>> pci_device_add()
> >>>  -> pci_init_capabilities()
> >>>   -> pci_enable_acs()
> >>>
> >>> Add code in the ACPI IORT SMMU platform devices initialization path
> >>> (that is called before ACPI PCI enumeration) to detect if an SMMU is
> >>> present in HW and enable PCI ACS if it actually is, restoring the
> >>> correct PCI ACS enablement sequencing.
> >>>
> >>> Fixes: f6810c15cf97 ("iommu/arm-smmu: Clean up early-probing
> >>> Signed-workarounds")
> >>> Signed-off-by: Lorenzo Pieralisi <[email-masked]>
> >>> Cc: Will Deacon <[email-masked]>
> >>> Cc: Robin Murphy <[email-masked]>
> >>> Cc: Zhou Wang <[email-masked]>
> >>> Cc: Alex Williamson <[email-masked]>
> >>> ---
> >>>  drivers/acpi/arm64/iort.c | 11 +++++++++++
> >>>  1 file changed, 11 insertions(+)
> >>>
> >>> diff --git a/drivers/acpi/arm64/iort.c b/drivers/acpi/arm64/iort.c
> >>> index 9565d57..71a7694 100644
> >>> --- a/drivers/acpi/arm64/iort.c
> >>> +++ b/drivers/acpi/arm64/iort.c
> >>> @@ -1184,6 +1184,7 @@ static void __init iort_init_platform_devices(void)
> >>>  	struct acpi_table_iort *iort;
> >>>  	struct fwnode_handle *fwnode;
> >>>  	int i, ret;
> >>> +	bool smmu_detected = false;
> >>>  
> >>>  	/*
> >>>  	 * iort_table and iort both point to the start of IORT table, but
> >>> @@ -1218,11 +1219,21 @@ static void __init iort_init_platform_devices(void)
> >>>  				acpi_free_fwnode_static(fwnode);
> >>>  				return;
> >>>  			}
> >>> +
> >>> +			smmu_detected = true;
> >>>  		}
> >>>  
> >>>  		iort_node = ACPI_ADD_PTR(struct acpi_iort_node, iort_node,
> >>>  					 iort_node->length);
> >>>  	}
> >>> +
> >>> +	/*
> >>> +	 * If IORT reports an SMMU component make sure PCI ACS is
> >>> +	 * requested so that PCI devices can enable it in their
> >>> +	 * capabilities.
> >>> +	 */
> >>> +	if (smmu_detected)
> >>> +		pci_request_acs();
> >>>  }
> >>>  
> >>>  void __init acpi_iort_init(void)
> >>>
> >>
> >> Hi Lorenzo,
> >>
> >> I tested this patch, it works well in my HiSilicon Hip08 based system.
> >> However, setting ACS flag at the stage of SMMU device init seems not good,
> >> I mean what if in one system there are only platform devices connected to
> >> SMMU device.
> > 
> > That's a fair point if you explain to me how current pci_request_acs()
> > usage copes with your remark above.
> 
> The current pci_request_acs usage for ARM SMMU-V3 sets ACS flags under CONFIG_PCI.
> However, as mentioned in your commit message, this setting is too late.
> 
> For the usage of X86 and AMD, as I am not familiar with the devices used in these
> two platforms, maybe the default devices in these platforms are PCIe based :)

I do not understand what your point is. ACS enablement is a global flag,
that is currently set whenever an x86/AMD/ARM IOMMU is detected/probed
AFAICS.

I agree that ACS enablement should be done before PCI enumeration,
for other comments either you are questioning the current policy
behind ACS enablement in the kernel - which can be a fair point - or
I do not understand what you mean.

Let me know since I would like to queue this patch unless I hear
a compelling objection to it.

Lorenzo