Re: [PATCH V1] PCI/AER: Configure ECRC only AER is native

From: Bjorn Helgaas <helgaas@kernel.org>
To: Sathyanarayanan Kuppuswamy  <sathyanarayanan.kuppuswamy@linux.intel.com>
Cc: Vidya Sagar <vidyas@nvidia.com>,
	bhelgaas@google.com, ruscur@russell.cc, oohall@gmail.com,
	treding@nvidia.com, jonathanh@nvidia.com, mmaddireddy@nvidia.com,
	kthota@nvidia.com, linux-pci@vger.kernel.org,
	linux-kernel@vger.kernel.org, vsethi@nvidia.com,
	linuxppc-dev@lists.ozlabs.org, sagar.tv@gmail.com
Subject: Re: [PATCH V1] PCI/AER: Configure ECRC only AER is native
Date: Wed, 11 Jan 2023 17:10:33 -0600	[thread overview]
Message-ID: <20230111231033.GA1714672@bhelgaas> (raw)
In-Reply-To: <a9126d49-6e98-956c-f4a3-699cc86d8b11@linux.intel.com>

On Wed, Jan 11, 2023 at 01:42:21PM -0800, Sathyanarayanan Kuppuswamy wrote:
> On 1/11/23 12:31 PM, Vidya Sagar wrote:
> > As the ECRC configuration bits are part of AER registers, configure
> > ECRC only if AER is natively owned by the kernel.
> 
> ecrc command line option takes "bios/on/off" as possible options. It
> does not clarify whether "on/off" choices can only be used if AER is
> owned by OS or it can override the ownership of ECRC configuration 
> similar to pcie_ports=native option. Maybe that needs to be clarified.

Good point, what do you think of an update like this:

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 6cfa6e3996cf..f7b40a439194 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -4296,7 +4296,9 @@
 				specified, e.g., 12@pci:8086:9c22:103c:198f
 				for 4096-byte alignment.
 		ecrc=		Enable/disable PCIe ECRC (transaction layer
-				end-to-end CRC checking).
+				end-to-end CRC checking).  Only effective
+				if OS has native AER control (either granted by
+				ACPI _OSC or forced via "pcie_ports=native").
 				bios: Use BIOS/firmware settings. This is the
 				the default.
 				off: Turn ECRC off

I don't know whether the "ecrc=" parameter is really needed.  If we
were adding it today, I would ask "why not enable ECRC wherever it is
supported?"  If there are devices where it's broken, we could always
add quirks to disable it on a case-by-case basis.

But I think the patch below is the right thing to do for now.  Vidya,
did you trip over an issue because of this, e.g., a conflict between
firmware use of AER and Linux use of it?  If so, maybe we could
mention a symptom on the commit log.  But my guess is you probably
found this by inspection.

Bjorn

> > Signed-off-by: Vidya Sagar <vidyas@nvidia.com>
> > ---
> >  drivers/pci/pcie/aer.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/drivers/pci/pcie/aer.c b/drivers/pci/pcie/aer.c
> > index e2d8a74f83c3..730b47bdcdef 100644
> > --- a/drivers/pci/pcie/aer.c
> > +++ b/drivers/pci/pcie/aer.c
> > @@ -184,6 +184,9 @@ static int disable_ecrc_checking(struct pci_dev *dev)
> >   */
> >  void pcie_set_ecrc_checking(struct pci_dev *dev)
> >  {
> > +	if (!pcie_aer_is_native(dev))
> > +		return;
> > +
> >  	switch (ecrc_policy) {
> >  	case ECRC_POLICY_DEFAULT:
> >  		return;
> 
> -- 
> Sathyanarayanan Kuppuswamy
> Linux Kernel Developer
