Message-ID: <20170201151807.GA15793@bhelgaas-glaptop.roam.corp.google.com>
Date:   Wed, 1 Feb 2017 09:18:07 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Vadim Lomovtsev <Vadim.Lomovtsev@...iumnetworks.com>
Cc:     David.Daney@...ium.com, tn@...ihalf.com,
        linux-kernel@...r.kernel.org,
        stemerkhanov@...IUMNETWORKS.onmicrosoft.com,
        linux-pci@...r.kernel.org, bhelgaas@...gle.com,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH] PCI: ACPI: Fix ThunderX PEM initialization

On Wed, Feb 01, 2017 at 04:53:25AM -0800, Vadim Lomovtsev wrote:
> On Tue, Jan 31, 2017 at 02:31:09PM -0600, Bjorn Helgaas wrote:
> > On Tue, Jan 31, 2017 at 06:57:20AM -0800, Vadim Lomovtsev wrote:
> > > On Tue, Jan 31, 2017 at 08:25:25AM -0600, Bjorn Helgaas wrote:
> > > > On Tue, Jan 31, 2017 at 02:28:30AM -0800, Vadim Lomovtsev wrote:
> > > > > Hi Bjorn,
> > > > > 
> > > > > On Mon, Jan 30, 2017 at 03:12:37PM -0600, Bjorn Helgaas wrote:
> > > > > > Hi Vadim,
> > > > > > 
> > > > > > On Mon, Jan 30, 2017 at 08:25:52AM -0800, Vadim Lomovtsev wrote:
> > > > > > > This patch is to address PEM initialization issue
> > > > > > > which causes network issues.
> > > > > > > 
> > > > > > > It is necessary to search for _HID:PNP0A08 while requesting
> > > > > > > PEM resources via ACPI instead of "THRX0002".
> > > > > > > 
> > > > > > > Signed-off-by: Vadim Lomovtsev <Vadim.Lomovtsev@...iumnetworks.com>
> > > > > > > ---
> > > > > > >  drivers/pci/host/pci-thunder-pem.c | 2 +-
> > > > > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > > > > > 
> > > > > > > diff --git a/drivers/pci/host/pci-thunder-pem.c b/drivers/pci/host/pci-thunder-pem.c
> > > > > > > index af722eb..aec30b8 100644
> > > > > > > --- a/drivers/pci/host/pci-thunder-pem.c
> > > > > > > +++ b/drivers/pci/host/pci-thunder-pem.c
> > > > > > > @@ -331,7 +331,7 @@ static int thunder_pem_acpi_init(struct pci_config_window *cfg)
> > > > > > >  	if (!res_pem)
> > > > > > >  		return -ENOMEM;
> > > > > > >  
> > > > > > > -	ret = acpi_get_rc_resources(dev, "THRX0002", root->segment, res_pem);
> > > > > > > +	ret = acpi_get_rc_resources(dev, "PNP0A08", root->segment, res_pem);
> > > > > > 
> > > > > > This doesn't smell right: PNP0A08 is the generic ACPI ID.  There's no
> > > > > > guarantee that if we find a PNP0A08 device, it is a ThunderX device.
> > > > > > 
> > > > > > I think the only way to call thunder_pem_acpi_init() is via an MCFG
> > > > > > quirk that mentions thunder_pem_ecam_ops, which means we only call it
> > > > > > if we find an MCFG with "CAVIUM" "THUNDERX" OEM and table IDs, so it's
> > > > > > probably safe in that sense.
> > > > > 
> > > > > Agree, it is not the best solution.
> > > > > We will implement such approach and send for review. 
> > > > > 
> > > > > > 
> > > > > > But it's an abuse of the ACPI _HID model.  If you match a device using
> > > > > > PNP0A08, all you can assume about it is that it uses the generic
> > > > > > PNP0A08 programming model, and I don't think that includes "the first
> > > > > > memory resource in _CRS contains ECAM space and MSI-X tables."
> > > > > > 
> > > > > > I expect this is a teething issue because you have firmware in the
> > > > > > field that uses PNP0A08 and it's not feasible to update it.  If that's
> > > > > > the case, the changelog should have details about it and we should
> > > > > > have a comment in the code, because I don't think this is the model we
> > > > > > want to end up with in future releases.
> > > > > 
> > > > > It could become so. However, for now I didn't get any reports on that,
> > > > > (may be I miss something) except some internal emailings.
> > > > > At my testing HW I was able to see some issues related to acpi-PEM stuff.
> > > > > 
> > > > > Thanks for feed-back, we will prepare another patch or patchset
> > > > > implementing approach you've highlighted.
> > > > 
> > > > The approach I would like best is to search for THRX0002, because then
> > > > you know you have a ThunderX PEM device, and you can assume
> > > > device-specific details about its _CRS.
> > > >
> > > > But that's what the existing code does, and apparently that doesn't
> > > > work.  My guess is that you have firmware in the field where the host
> > > > bridge has only PNP0A08 (and maybe PNP0A03) as device IDs.
> > > 
> > > Because there is no such ACPI ID as "THRX0002" registered
> > > (http://www.uefi.org/acpi_id_list).
> > 
> > To be pedantically correct, I think you want "THRX" registered.  Then
> > you can manage the "0002" part internally without registering each
> > individual device.
> 
> Not sure if it would be registered that way, because (AFAIK)
> it expected to be string constructed from Vendor ID (not the Product ID) plus
> four hex digit manged internaly. So we suggest to change it to 177DXXXX
> which corresponds to Cavium PCI ID https://pci-ids.ucw.cz/pci.ids.
> It's also possible to use the 3-digit PNP ID, "CAV", to construct these
> _HID/_CID/_SUB values (http://www.uefi.org/pnp_id_list).

My point was that you only need to register the prefix ("CAV" or
"THRX") of the PNP or ACPI ID.  Then you manage the suffixes
internally.  You as long as you register "CAV" or "THRX", you can
assign and use "THRX0002" yourself without registering that
specifically.

> So the FW will be updated accordingly.
> 
> For old FW we'll implement fallback scenario gathering resource info
> via _CRS object (comments will be provided in the code also).
> 
> > 
> > > From the other hand we may gather device resources through
> > > _CRS (we have acpi_device already set by this moment) but
> > > we need to be sure that we're running at Cavium ThunderX board then.
> > > 
> > > To do that we may add _SUB value (accrodingly to spec) with
> > > exact ID string (a full PCI ID value "177DA22D" is suggested).
> > > This will eventually become the main method of finding out
> > > whether we run on a ThunderX PEM.
> > 
> > I don't understand why you would use _SUB.  I think the correct way to
> > handle this is to use a _HID of "THRX0002" with a _CID of "PNP0A08".
> > Is there some existing _SUB usage you're using as an example?
> 
> Here we were talking about extra quirk to match PEM and ECAM and thus make
> a decision. This object could also store some vendor-specific IDs.
> To be honest I didn't see usage in kernel (didn't search), but ACPI Spec
> provide an example as (p 6.1.9) :
>   Name (_SUB, "MSFT3000")// Vendor-defined subsystem
> 
> However this is still debatable and we probably stick to _HID while
> implementing additional match functions.

If you want a driver to bind to a specific device, e.g., the ThunderX
PCI host bridge, the firmware should use a unique _HID in the ACPI
namespace and the driver should claim that _HID.

It's conceivable that you could use _SUB, but that's needlessly
different from everything else.

Bjorn

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