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

From: [email-masked] (Lorenzo Pieralisi)
Date: Fri, 22 Sep 2017 10:45:46 +0100

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.

Lorenzo