linux-kernel - Re: [PATCH v6] PCI: quirks: update Cavium ThunderX ACS quirk implementation

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Date:   Tue, 17 Oct 2017 04:29:24 -0700
From:   Vadim Lomovtsev <Vadim.Lomovtsev@...iumnetworks.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     bhelgaas@...gle.com, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org, Wilson.Snyder@...ium.com,
        alex.williamson@...hat.com, David Daney <david.daney@...ium.com>,
        Manish Jaggi <mjaggi@...iumnetworks.com>,
        vadim.lomovtsev@...ium.com
Subject: Re: [PATCH v6] PCI: quirks: update Cavium ThunderX ACS quirk
 implementation

On Mon, Oct 16, 2017 at 04:23:20PM -0500, Bjorn Helgaas wrote:
Hi Bjorn,

> [+cc David, Manish]
> 
> Please use a subject line that tells more about what's going on.
> "Update quirk" doesn't really convey any useful information.
> Something like "Apply Cavium ThunderX ACS quirk only to Root Ports".
> 
> On Wed, Sep 27, 2017 at 11:20:39AM -0700, Vadim Lomovtsev wrote:
> > This commit makes Cavium PCI ACS quirk applicable only to Cavium
> > ThunderX (CN8XXX) family PCIE Root Ports which has limited PCI capabilities
> > in terms of no ACS support advertisement. However, the RTL internally
> > implements similar protection as if ACS had completion/request redirection,
> > upstream forwarding and validation features enabled.
> > 
> > Current quirk implementation doesn't take into account PCIERCs which
> > also needs to be quirked. So the pci device id check mask is updated
> > and check of device ID moved into separate function.
> 
> s/PCIE/PCIe/ above
> 
> s/PCIERCs/PCIe Root Ports/ (I assume, since usually a Root Complex
> itself doesn't appear as a pci_dev)
> 
> > Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@...iumnetworks.com>
> > ---
> > 	v5 -> v6: comment typo fix: change 0xa00 to 0xa000
> > 
> >  drivers/pci/quirks.c | 29 +++++++++++++++++++++--------
> >  1 file changed, 21 insertions(+), 8 deletions(-)
> > 
> > diff --git a/drivers/pci/quirks.c b/drivers/pci/quirks.c
> > index a4d3361..ed6c76d 100644
> > --- a/drivers/pci/quirks.c
> > +++ b/drivers/pci/quirks.c
> > @@ -4211,20 +4211,33 @@ static int pci_quirk_amd_sb_acs(struct pci_dev *dev, u16 acs_flags)
> >  #endif
> >  }
> >  
> > -static int pci_quirk_cavium_acs(struct pci_dev *dev, u16 acs_flags)
> > +/*
> > + * The Cavium downstream ports doesn't advertise their ACS capability registers.
> > + * However, the RTL internally implements similar protection as if
> > + * ACS had completion redirection, forwarding and validation features enabled.
> > + * So by this flags we're asserting that the hardware implements and
> > + * enables equivalent ACS functionality for these flags.
> > + */
> > +#define CAVIUM_CN8XXX_ACS_FLAGS (PCI_ACS_RR | PCI_ACS_CR | PCI_ACS_SV | PCI_ACS_UF)
> 
> You are changing the set of flags, which isn't mentioned in the changelog.
> I think the best thing would be to have two patches: one that changes the
> set of flags and a second that changes the set of affected devices.
> 
> This set of flags was used twice in the original patch, so a #define made
> sense.  But now you only use it once, so there's no benefit in adding the
> #define, and adding it makes the change in the set of flags harder to see.
> 
> > +static __inline__  bool pci_quirk_cavium_acs_match(struct pci_dev *dev)
> 
> No need to use "__inline__" here.  This isn't performance critical,
> and the compiler will probably inline it anyway because there's only
> one use.
>
> >  {
> >  	/*
> > -	 * Cavium devices matching this quirk do not perform peer-to-peer
> > -	 * with other functions, allowing masking out these bits as if they
> > -	 * were unimplemented in the ACS capability.
> > +	 * Effectively selects all downstream ports for whole ThunderX 1 family
> > +	 * by 0xa000 mask (which represents 8 SoCs), while the lower bits of device ID
> > +	 * are used to indicate which subdevice is used within the SoC.
> 
> Please wrap your comments so they fit in 80 columns.
> 
> >  	 */
> > -	acs_flags &= ~(PCI_ACS_SV | PCI_ACS_TB | PCI_ACS_RR |
> > -		       PCI_ACS_CR | PCI_ACS_UF | PCI_ACS_DT);
> > +	return (pci_is_pcie(dev) &&
> > +		(pci_pcie_type(dev) == PCI_EXP_TYPE_ROOT_PORT) &&
> > +		((dev->device & 0xf800) == 0xa000));
> 
> I'm just a little confused by the 0xa000 mask you refer to in the
> comment, because the mask in the code is 0xf800.

Sorry for confusion, will correct it to 0xf800 for comment.

> 
> Previously the quirk applied to all Cavium device IDs in the range
> 0xa000-0xa0ff.  Now it applies to device IDs in the range
> 0xa000-0xa7ff, but only if they are PCIe Root Ports.  Right?

Correct. Since this quirk is necessary for Root Ports only.

Thanks for reply, I'll re-work this one accordingly to your comments and re-send v7.

WBR,
Vadim

> 
> > +}
> >  
> > -	if (!((dev->device >= 0xa000) && (dev->device <= 0xa0ff)))
> > +static int pci_quirk_cavium_acs(struct pci_dev *dev, u16 acs_flags)
> > +{
> > +	if (!pci_quirk_cavium_acs_match(dev))
> >  		return -ENOTTY;
> >  
> > -	return acs_flags ? 0 : 1;
> > +	return acs_flags & ~(CAVIUM_CN8XXX_ACS_FLAGS) ? 0 : 1;
> >  }
> >  
> >  static int pci_quirk_xgene_acs(struct pci_dev *dev, u16 acs_flags)
> > -- 
> > 2.4.11
> >