Message-ID: <68dd87c8866f9_298010093@dwillia2-mobl4.notmuch>
Date: Wed, 1 Oct 2025 12:58:00 -0700
From: <dan.j.williams@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>,
	<dan.j.williams@...el.com>
CC: Xu Yilun <yilun.xu@...ux.intel.com>, <linux-coco@...ts.linux.dev>,
	<linux-pci@...r.kernel.org>, <yilun.xu@...el.com>,
	<baolu.lu@...ux.intel.com>, <zhenzhong.duan@...el.com>,
	<aneesh.kumar@...nel.org>, <bhelgaas@...gle.com>, <aik@....com>, LKML
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 2/3] PCI/IDE: Add Address Association Register setup for
 RP

Ilpo Järvinen wrote:
> On Tue, 30 Sep 2025, dan.j.williams@...el.com wrote:
> > Ilpo Järvinen wrote:
> > > On Sun, 28 Sep 2025, Xu Yilun wrote:
> > > 
> > > > Add Address Association Register setup for Root Ports.
> > > > 
> > > > The address ranges for RP side Address Association Registers should
> > > > cover memory addresses for all PFs/VFs/downstream devices of the DSM
> > > > device. A simple solution is to get the aggregated 32-bit and 64-bit
> > > > address ranges from directly connected downstream port (either an RP or
> > > > a switch port) and set into 2 Address Association Register blocks.
> > > > 
> > > > There is a case the platform doesn't require Address Association
> > > > Registers setup and provides no register block for RP (AMD). Will skip
> > > > the setup in pci_ide_stream_setup().
> > > > 
> > > > Also imaging another case where there is only one block for RP.
> > > > Prioritize 64-bit address ranges setup for it. No strong reason for the
> > > > preference until a real use case comes.
> > > > 
> > > > The Address Association Register setup for Endpoint Side is still
> > > > uncertain so isn't supported in this patch.
> > > > 
> > > > Take the oppotunity to export some mini helpers for Address Association
> > > > Registers setup. TDX Connect needs the provided aggregated address
> > > > ranges but will use specific firmware calls for actual setup instead of
> > > > pci_ide_stream_setup().
> > > > 
> > > > Co-developed-by: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
> > > > Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@...nel.org>
> > > > Co-developed-by: Arto Merilainen <amerilainen@...dia.com>
> > > > Signed-off-by: Arto Merilainen <amerilainen@...dia.com>
> > > > Signed-off-by: Xu Yilun <yilun.xu@...ux.intel.com>
> > > > ---
> > > >  include/linux/pci-ide.h | 11 +++++++
> > > >  drivers/pci/ide.c       | 64 ++++++++++++++++++++++++++++++++++++++++-
> > > >  2 files changed, 74 insertions(+), 1 deletion(-)
> > > > 
> > > > diff --git a/include/linux/pci-ide.h b/include/linux/pci-ide.h
> > > > index 5adbd8b81f65..ac84fb611963 100644
> > > > --- a/include/linux/pci-ide.h
> > > > +++ b/include/linux/pci-ide.h
> > > > @@ -6,6 +6,15 @@
> > > >  #ifndef __PCI_IDE_H__
> > > >  #define __PCI_IDE_H__
> > > >  
> > > > +#define SEL_ADDR1_LOWER GENMASK(31, 20)
> > > > +#define SEL_ADDR_UPPER GENMASK_ULL(63, 32)
> > > > +#define PREP_PCI_IDE_SEL_ADDR1(base, limit)                    \
> > > > +	(FIELD_PREP(PCI_IDE_SEL_ADDR_1_VALID, 1) |             \
> > > > +	 FIELD_PREP(PCI_IDE_SEL_ADDR_1_BASE_LOW,          \
> > > > +		    FIELD_GET(SEL_ADDR1_LOWER, (base))) | \
> > > > +	 FIELD_PREP(PCI_IDE_SEL_ADDR_1_LIMIT_LOW,         \
> > > > +		    FIELD_GET(SEL_ADDR1_LOWER, (limit))))
> > > > +
> > > >  #define PREP_PCI_IDE_SEL_RID_2(base, domain)               \
> > > >  	(FIELD_PREP(PCI_IDE_SEL_RID_2_VALID, 1) |          \
> > > >  	 FIELD_PREP(PCI_IDE_SEL_RID_2_BASE, (base)) | \
> > > > @@ -42,6 +51,8 @@ struct pci_ide_partner {
> > > >  	unsigned int default_stream:1;
> > > >  	unsigned int setup:1;
> > > >  	unsigned int enable:1;
> > > > +	struct range mem32;
> > > > +	struct range mem64;
> > > >  };
> > > >  
> > > >  /**
> > > > diff --git a/drivers/pci/ide.c b/drivers/pci/ide.c
> > > > index 7633b8e52399..8db1163737e5 100644
> > > > --- a/drivers/pci/ide.c
> > > > +++ b/drivers/pci/ide.c
> > > > @@ -159,7 +159,11 @@ struct pci_ide *pci_ide_stream_alloc(struct pci_dev *pdev)
> > > >  	struct stream_index __stream[PCI_IDE_HB + 1];
> > > >  	struct pci_host_bridge *hb;
> > > >  	struct pci_dev *rp;
> > > > +	struct pci_dev *br;
> > > 
> > > Why not join with the previous line?
> > > 
> > > >  	int num_vf, rid_end;
> > > > +	struct range mem32 = {}, mem64 = {};
> > > > +	struct pci_bus_region region;
> > > > +	struct resource *res;
> > > >  
> > > >  	if (!pci_is_pcie(pdev))
> > > >  		return NULL;
> > > > @@ -206,6 +210,24 @@ struct pci_ide *pci_ide_stream_alloc(struct pci_dev *pdev)
> > > >  	else
> > > >  		rid_end = pci_dev_id(pdev);
> > > >  
> > > > +	br = pci_upstream_bridge(pdev);
> > > > +	if (!br)
> > > > +		return NULL;
> > > > +
> > > > +	res = &br->resource[PCI_BRIDGE_MEM_WINDOW];
> > > 
> > > pci_resource_n()
> > > 
> > > > +	if (res->flags & IORESOURCE_MEM) {
> > > > +		pcibios_resource_to_bus(br->bus, &region, res);
> > > > +		mem32.start = region.start;
> > > > +		mem32.end = region.end;
> > > > +	}
> > > > +
> > > > +	res = &br->resource[PCI_BRIDGE_PREF_MEM_WINDOW];
> > > 
> > > Ditto.
> > > 
> > > > +	if (res->flags & IORESOURCE_PREFETCH) {
> > > 
> > > While I don't know much about what's going on here, is this assuming the 
> > > bridge window is not disabled solely based on this flag check?
> > 
> > Indeed it does seem to be assumining that the flag is only set when the
> > resource is valid and active.
> > 
> > > Previously inactive bridge window flags were reset but that's no longer 
> > > the case after the commit 8278c6914306 ("PCI: Preserve bridge window 
> > > resource type flags") (currently in pci/resource)?
> > 
> > Thanks for the heads up. It does seem odd that both IORESOURCE_UNSET and
> > IORESOURCE_DISABLED are both being set and the check allows for either.
> 
> I'm a bit lost on what check you're referring to.
> 
> If you refer to the check in pci_bus_alloc_from_region() added by that 
> commit, now that I relook at it, it would probably be better written as 
> !r->parent (a TODO entry added to verify it).
> 
> > Is that assuming that other call paths not touched in that set may only
> > set one of those flags?
> 
> Presence of either of those flags indicates the bridge window resource is 
> not usable "normally". There's also res->parent which directly tells if 
> the resource is assigned. Out of those three, res->parent is the preferred 
> way to know if the resource is usable normally (aka. "assigned"), however, 
> res->parent check can only be used if this code runs late enough.
> 
> To me IORESOURCE_UNSET looks unnecessary flag and would want to get rid of 
> it entirely as res->parent mostly tells the same information. But I don't 
> expect that to be an easy change, and there's also the init transient 
> where res->parent is not yet set which complicates things.
> 
> But until IORESOURCE_UNSET is gone, it alone can indicate the resource is 
> not in usable state. And so can IORESOURCE_DISABLED.
> 
> The resource fitting code clears DISABLED (while sizing bridge windows) 
> before UNSET (on assignment), so they have different meaning even if 
> there's overlap on the consumer side depending on use case. The resource 
> fitting/assignment code cares for this distinction, see e.g. 
> pdev_resource_assignable() which only checks for DISABLED because, well, 
> we're about to attempt to turn UNSET into !UNSET.

Thanks for the details!

> > Otherwise, the change to mark the resource as zero-sized feels a better
> > / more explicit protocol than checking for flags. IDE setup only cares
> > that any downstream MMIO get included in the stream.
> 
> If this particular code here runs after resources have been assigned by 
> the kernel, please check res->parent to know if the resource is assigned 
> or not.
> 
> I'm considering adding resource_assigned() helper for this purpose as 
> res->parent check looks too odd and may alienate developers from using it 
> if they don't know about the internals of the resource management.
> 
> If the bridge window resource is assigned, it should have the expected 
> flags and IMO it's useless to check for the flags (if flags are not right 
> for the bridge window resources that is assigned, we've a bug elsewhere in 
> the code).
> 
> 
> As a sidenote, there are lots of !res->flags and !pci_resource_len(...), 
> etc. checks which are often custom implementations resource_assigned(), 
> they all are landmines that make my life harder as I'd want to make 
> further improvements to resource behavior.

A resource_assigned() helper sounds good to me. I will fold that into
this patch for now, but feel free to pull that out and merge separately
if you need it in other places.

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