linux-kernel - Re: [PATCH v6 8/8] PCI: hv: Turn on the host bridge probing on ARM64

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Date:   Mon, 9 Aug 2021 22:38:48 +0800
From:   Boqun Feng <boqun.feng@...il.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>,
        Marc Zyngier <maz@...nel.org>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will@...nel.org>,
        "K. Y. Srinivasan" <kys@...rosoft.com>,
        Haiyang Zhang <haiyangz@...rosoft.com>,
        Stephen Hemminger <sthemmin@...rosoft.com>,
        Wei Liu <wei.liu@...nel.org>, Dexuan Cui <decui@...rosoft.com>,
        Rob Herring <robh@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linux-hyperv@...r.kernel.org, linux-pci@...r.kernel.org,
        Sunil Muthuswamy <sunilmut@...rosoft.com>,
        Mike Rapoport <rppt@...nel.org>
Subject: Re: [PATCH v6 8/8] PCI: hv: Turn on the host bridge probing on ARM64

On Tue, Aug 03, 2021 at 06:14:51PM +0100, Lorenzo Pieralisi wrote:
> On Tue, Jul 27, 2021 at 02:06:57AM +0800, Boqun Feng wrote:
> > Now we have everything we need, just provide a proper sysdata type for
> > the bus to use on ARM64 and everything else works.
> > 
> > Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> > ---
> >  drivers/pci/controller/pci-hyperv.c | 7 +++++++
> >  1 file changed, 7 insertions(+)
> > 
> > diff --git a/drivers/pci/controller/pci-hyperv.c b/drivers/pci/controller/pci-hyperv.c
> > index e6276aaa4659..62dbe98d1fe1 100644
> > --- a/drivers/pci/controller/pci-hyperv.c
> > +++ b/drivers/pci/controller/pci-hyperv.c
> > @@ -40,6 +40,7 @@
> >  #include <linux/kernel.h>
> >  #include <linux/module.h>
> >  #include <linux/pci.h>
> > +#include <linux/pci-ecam.h>
> >  #include <linux/delay.h>
> >  #include <linux/semaphore.h>
> >  #include <linux/irqdomain.h>
> > @@ -448,7 +449,11 @@ enum hv_pcibus_state {
> >  };
> >  
> >  struct hv_pcibus_device {
> > +#ifdef CONFIG_X86
> >  	struct pci_sysdata sysdata;
> > +#elif defined(CONFIG_ARM64)
> > +	struct pci_config_window sysdata;
> 
> This is ugly. HV does not need pci_config_window at all right
> (other than arm64 pcibios_root_bridge_prepare()) ?
> 

Right.

> The issue is that in HV you have to have *some* sysdata != NULL, it is
> just some data to retrieve the hv_pcibus_device.
> 
> Mmaybe we can rework ARM64 ACPI code to store the acpi_device in struct
> pci_host_bridge->private instead of retrieving it from pci_config_window
> so that we decouple HV from the ARM64 back-end.
> 
> HV would just set struct pci_host_bridge->private == NULL.
> 

Works for me, but please note that pci_sysdata is an x86-specific
structure, so we still need to define a fake pci_sysdata inside
pci-hyperv.c, like:

	#ifndef CONFIG_X86
	struct pci_sysdata { };
	#end

> I need to think about this a bit, I don't think it should block
> this series though but it would be nicer.

After a quick look into the code, seems that what we need to do is to
add an additional parameter for acpi_pci_root_create() and introduce a
slightly different version of pci_create_root_bus(). A question is:
should we only do this for ARM64, or should we also do this for
other acpi_pci_root_create() users (x86 and ia64)? Another question
comes to my mind is, while we are at it, is there anything else that we
want to move from sysdata to ->private? These questions are out of scope
of this patchset, I think. Maybe it's better that we address them in the
future, and I can send out separate RFC patches to start the discussion.
Does that sound like a plan to you?

Regards,
Boqun

> 
> Lorenzo
> 
> > +#endif
> >  	struct pci_host_bridge *bridge;
> >  	struct fwnode_handle *fwnode;
> >  	/* Protocol version negotiated with the host */
> > @@ -3075,7 +3080,9 @@ static int hv_pci_probe(struct hv_device *hdev,
> >  			 dom_req, dom);
> >  
> >  	hbus->bridge->domain_nr = dom;
> > +#ifdef CONFIG_X86
> >  	hbus->sysdata.domain = dom;
> > +#endif
> >  
> >  	hbus->hdev = hdev;
> >  	INIT_LIST_HEAD(&hbus->children);
> > -- 
> > 2.32.0
> >