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

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Message-ID: <YR5MaiCZrFJ71AwY@boqun-archlinux>
Date:   Thu, 19 Aug 2021 20:19:54 +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

Hi,

On Mon, Aug 09, 2021 at 04:53:43PM +0100, Lorenzo Pieralisi wrote:
> On Mon, Aug 09, 2021 at 10:38:48PM +0800, Boqun Feng wrote:
> > 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?
> 
> Yes it does and we can start from ARM64 - what I really don't like
> is the arch/arm64 dependency with the HV controller driver as I
> described, being forced to have a struct pci_config_window in the
> driver is not really nice or clean IMO.
> 
> Not that I expect any other PCI host bridge driver with ACPI coming
> anytime soon but even if it is not within set (that we can merge) I'd
> like to see the decoupling rework done asap, let me put it this way.
> 

Just want to check whether the following is a good starter for the
decoupling rework?

	https://lore.kernel.org/lkml/20210811153619.88922-1-boqun.feng@gmail.com/

If so, is there any other concern about taking this patchset? ;-)

Regards,
Boqun

> Thanks,
> Lorenzo
> 
> > 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
> > > >