linux-kernel - Re: [PATCH v5 1/6] PCI/IOV: Restore VF resizable BAR state after reset

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Message-ID: <xbtcs6tzggmpv4icelgzhpixad23evefcf6jjsxi74qkjvxyue@mzb67hniua4o>
Date: Mon, 17 Mar 2025 12:21:56 +0100
From: Michał Winiarski <michal.winiarski@...el.com>
To: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
CC: <linux-pci@...r.kernel.org>, <intel-xe@...ts.freedesktop.org>,
	<dri-devel@...ts.freedesktop.org>, LKML <linux-kernel@...r.kernel.org>,
	"Bjorn Helgaas" <bhelgaas@...gle.com>, Christian König
	<christian.koenig@....com>, Krzysztof Wilczyński
	<kw@...ux.com>, Rodrigo Vivi <rodrigo.vivi@...el.com>, Michal Wajdeczko
	<michal.wajdeczko@...el.com>, Lucas De Marchi <lucas.demarchi@...el.com>,
	Thomas Hellström <thomas.hellstrom@...ux.intel.com>,
	"Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>, Maxime Ripard
	<mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>, David Airlie
	<airlied@...il.com>, Simona Vetter <simona@...ll.ch>, Matt Roper
	<matthew.d.roper@...el.com>
Subject: Re: [PATCH v5 1/6] PCI/IOV: Restore VF resizable BAR state after
 reset

On Thu, Mar 13, 2025 at 11:50:37AM +0200, Ilpo Järvinen wrote:
> On Thu, 13 Mar 2025, Ilpo Järvinen wrote:
> 
> > On Wed, 12 Mar 2025, Michał Winiarski wrote:
> > 
> > > Similar to regular resizable BAR, VF BAR can also be resized, e.g. by
> > > the system firmware or the PCI subsystem itself.
> > > 
> > > Add the capability ID and restore it as a part of IOV state.
> > > 
> > > See PCIe r4.0, sec 9.3.7.4.
> > > 
> > > Signed-off-by: Michał Winiarski <michal.winiarski@...el.com>
> > > Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@...ux.intel.com>
> > > Reviewed-by: Christian König <christian.koenig@....com>
> > > ---
> > >  drivers/pci/iov.c             | 29 ++++++++++++++++++++++++++++-
> > >  include/uapi/linux/pci_regs.h |  1 +
> > >  2 files changed, 29 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/pci/iov.c b/drivers/pci/iov.c
> > > index 121540f57d4bf..eb4d33eacacb8 100644
> > > --- a/drivers/pci/iov.c
> > > +++ b/drivers/pci/iov.c
> > > @@ -7,6 +7,7 @@
> > >   * Copyright (C) 2009 Intel Corporation, Yu Zhao <yu.zhao@...el.com>
> > >   */
> > >  
> > > +#include <linux/bitfield.h>
> > >  #include <linux/pci.h>
> > >  #include <linux/slab.h>
> > >  #include <linux/export.h>
> > > @@ -868,6 +869,30 @@ static void sriov_release(struct pci_dev *dev)
> > >  	dev->sriov = NULL;
> > >  }
> > >  
> > > +static void sriov_restore_vf_rebar_state(struct pci_dev *dev)
> > > +{
> > > +	unsigned int pos, nbars, i;
> > > +	u32 ctrl;
> > > +
> > > +	pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_VF_REBAR);
> > > +	if (!pos)
> > > +		return;
> > 
> > FYI, the commit f7c9bb759161 ("PCI: Cache offset of Resizable BAR 
> > capability") which is currently in pci/enumeration makes this simpler.
> 
> I'm sorry, I realized it's not the same capability but you should do 
> similar thing for VF rebar capability as caching the value of 
> pci_find_ext_capability() avoids some slowness during save/restore.

The series was based on pci/resource due to other dependencies.
But yeah - point taken, I'll use caching in next revision.

Thanks,
-Michał

> 
> -- 
>  i.
> 
> > > +	pci_read_config_dword(dev, pos + PCI_REBAR_CTRL, &ctrl);
> > > +	nbars = FIELD_GET(PCI_REBAR_CTRL_NBAR_MASK, ctrl);
> > > +
> > > +	for (i = 0; i < nbars; i++, pos += 8) {
> > > +		int bar_idx, size;
> > > +
> > > +		pci_read_config_dword(dev, pos + PCI_REBAR_CTRL, &ctrl);
> > > +		bar_idx = FIELD_GET(PCI_REBAR_CTRL_BAR_IDX, ctrl);
> > > +		size = pci_rebar_bytes_to_size(dev->sriov->barsz[bar_idx]);
> > > +		ctrl &= ~PCI_REBAR_CTRL_BAR_SIZE;
> > > +		ctrl |= FIELD_PREP(PCI_REBAR_CTRL_BAR_SIZE, size);
> > > +		pci_write_config_dword(dev, pos + PCI_REBAR_CTRL, ctrl);
> > > +	}
> > > +}
> > > +
> > >  static void sriov_restore_state(struct pci_dev *dev)
> > >  {
> > >  	int i;
> > > @@ -1027,8 +1052,10 @@ resource_size_t pci_sriov_resource_alignment(struct pci_dev *dev, int resno)
> > >   */
> > >  void pci_restore_iov_state(struct pci_dev *dev)
> > >  {
> > > -	if (dev->is_physfn)
> > > +	if (dev->is_physfn) {
> > > +		sriov_restore_vf_rebar_state(dev);
> > >  		sriov_restore_state(dev);
> > > +	}
> > >  }
> > >  
> > >  /**
> > > diff --git a/include/uapi/linux/pci_regs.h b/include/uapi/linux/pci_regs.h
> > > index 3c2558b98d225..aadd483c47d6f 100644
> > > --- a/include/uapi/linux/pci_regs.h
> > > +++ b/include/uapi/linux/pci_regs.h
> > > @@ -744,6 +744,7 @@
> > >  #define PCI_EXT_CAP_ID_L1SS	0x1E	/* L1 PM Substates */
> > >  #define PCI_EXT_CAP_ID_PTM	0x1F	/* Precision Time Measurement */
> > >  #define PCI_EXT_CAP_ID_DVSEC	0x23	/* Designated Vendor-Specific */
> > > +#define PCI_EXT_CAP_ID_VF_REBAR 0x24	/* VF Resizable BAR */
> > >  #define PCI_EXT_CAP_ID_DLF	0x25	/* Data Link Feature */
> > >  #define PCI_EXT_CAP_ID_PL_16GT	0x26	/* Physical Layer 16.0 GT/s */
> > >  #define PCI_EXT_CAP_ID_NPEM	0x29	/* Native PCIe Enclosure Management */
> > > 
> > 
> >