Re: [PATCH] PCI: Add PCIE ACS quirk for IPROC PAXB

[Alex Williamson <alex.williamson@redhat.com>]

On Thu, 5 Sep 2019 17:26:49 -0500
Bjorn Helgaas <helgaas@kernel.org> wrote:

> [+cc Alex]
> 
> On Tue, Aug 20, 2019 at 10:09:45AM +0530, Srinath Mannam wrote:
> > From: Abhinav Ratna <abhinav.ratna@broadcom.com>
> > 
> > IPROC PAXB RC doesn't support ACS capabilities and control registers.
> > Add quirk to have separate IOMMU groups for all EPs and functions connected
> > to root port, by masking RR/CR/SV/UF bits.
> > 
> > Signed-off-by: Abhinav Ratna <abhinav.ratna@broadcom.com>
> > Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>  
> 
> I tentatively applied this to pci/misc with Scott's ack for v5.4.
> 
> I tweaked the patch itself to follow the style of similar quirks
> (interdiff is below, plus a diff of the commit log).  Please make sure
> I didn't break it.
> 
> I also went out on a limb and reworded the comment to give what I
> *think* is the justification for this patch, as opposed to merely a
> description of the code.  I'm making a lot of assumptions there, so
> please confirm that they're correct, or supply alternate justification
> if they're not.

Agreed, this really needs to be the vendor vouching for ACS equivalent
functionality, not simply splitting IOMMU groups because it's
inconvenient.  Thanks,

Alex

> 
> > ---
> >  drivers/pci/quirks.c | 16 ++++++++++++++++
> >  1 file changed, 16 insertions(+)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index 0f16acc..f9584c0 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4466,6 +4466,21 @@ static int pci_quirk_mf_endpoint_acs(struct pci_dev *dev, u16 acs_flags)
> >  	return acs_flags ? 0 : 1;
> >  }
> >  
> > +static int pcie_quirk_brcm_bridge_acs(struct pci_dev *dev, u16 acs_flags)
> > +{
> > +	/*
> > +	 * IPROC PAXB RC doesn't support ACS capabilities and control registers.
> > +	 * Add quirk to to have separate IOMMU groups for all EPs and functions
> > +	 * connected to root port, by masking RR/CR/SV/UF bits.
> > +	 */
> > +
> > +	u16 flags = (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_SV);
> > +	int ret = acs_flags & ~flags ? 0 : 1;
> > +
> > +	return ret;
> > +}
> > +
> > +
> >  static const struct pci_dev_acs_enabled {
> >  	u16 vendor;
> >  	u16 device;
> > @@ -4559,6 +4574,7 @@ static const struct pci_dev_acs_enabled {
> >  	{ PCI_VENDOR_ID_AMPERE, 0xE00A, pci_quirk_xgene_acs },
> >  	{ PCI_VENDOR_ID_AMPERE, 0xE00B, pci_quirk_xgene_acs },
> >  	{ PCI_VENDOR_ID_AMPERE, 0xE00C, pci_quirk_xgene_acs },
> > +	{ PCI_VENDOR_ID_BROADCOM, 0xD714, pcie_quirk_brcm_bridge_acs },
> >  	{ 0 }
> >  };  
> 
> diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> index 77c0330ac922..2edbce35e8c5 100644
> --- a/drivers/pci/quirks.c
> +++ b/drivers/pci/quirks.c
> @@ -4466,21 +4466,19 @@ static int pci_quirk_mf_endpoint_acs(struct pci_dev *dev, u16 acs_flags)
>  	return acs_flags ? 0 : 1;
>  }
>  
> -static int pcie_quirk_brcm_bridge_acs(struct pci_dev *dev, u16 acs_flags)
> +static int pci_quirk_brcm_acs(struct pci_dev *dev, u16 acs_flags)
>  {
>  	/*
> -	 * IPROC PAXB RC doesn't support ACS capabilities and control registers.
> -	 * Add quirk to to have separate IOMMU groups for all EPs and functions
> -	 * connected to root port, by masking RR/CR/SV/UF bits.
> +	 * iProc PAXB Root Ports don't advertise an ACS capability, but
> +	 * they do not allow peer-to-peer transactions between Root Ports.
> +	 * Allow each Root Port to be in a separate IOMMU group by masking
> +	 * SV/RR/CR/UF bits.
>  	 */
> +	acs_flags &= ~(PCI_ACS_SV | PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF);
>  
> -	u16 flags = (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_SV);
> -	int ret = acs_flags & ~flags ? 0 : 1;
> -
> -	return ret;
> +	return acs_flags ? 0 : 1;
>  }
>  
> -
>  static const struct pci_dev_acs_enabled {
>  	u16 vendor;
>  	u16 device;
> @@ -4574,7 +4572,7 @@ static const struct pci_dev_acs_enabled {
>  	{ PCI_VENDOR_ID_AMPERE, 0xE00A, pci_quirk_xgene_acs },
>  	{ PCI_VENDOR_ID_AMPERE, 0xE00B, pci_quirk_xgene_acs },
>  	{ PCI_VENDOR_ID_AMPERE, 0xE00C, pci_quirk_xgene_acs },
> -	{ PCI_VENDOR_ID_BROADCOM, 0xD714, pcie_quirk_brcm_bridge_acs },
> +	{ PCI_VENDOR_ID_BROADCOM, 0xD714, pci_quirk_brcm_acs },
>  	{ 0 }
>  };
>  
> 
> 
> 
> @@ -1,49 +1,49 @@
> -commit b50ae502eff0
> +commit 46b2c32df7a4
>  Author: Abhinav Ratna <abhinav.ratna@broadcom.com>
>  Date:   Tue Aug 20 10:09:45 2019 +0530
>  
> -    PCI: Add PCIE ACS quirk for IPROC PAXB
> +    PCI: Add ACS quirk for iProc PAXB
>      
> -    IPROC PAXB RC doesn't support ACS capabilities and control registers.
> -    Add quirk to have separate IOMMU groups for all EPs and functions connected
> -    to root port, by masking RR/CR/SV/UF bits.
> +    iProc PAXB Root Ports don't advertise an ACS capability, but they do not
> +    allow peer-to-peer transactions between Root Ports.  Add an ACS quirk so
> +    each Root Port can be in a separate IOMMU group.
>      
> +    [bhelgaas: commit log, comment, use common implementation style]
>      Link: https://lore.kernel.org/r/1566275985-25670-1-git-send-email-srinath.mannam@broadcom.com
>      Signed-off-by: Abhinav Ratna <abhinav.ratna@broadcom.com>
>      Signed-off-by: Srinath Mannam <srinath.mannam@broadcom.com>
>      Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> +    Acked-by: Scott Branden <scott.branden@broadcom.com>
>