linux-kernel - Re: [PATCH v2 1/2] powerpc/pci: Add config option for using OF 'reg' for PCI domain

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Message-ID: <20220715171132.ujaexzm4ipad7o4f@pali>
Date:   Fri, 15 Jul 2022 19:11:32 +0200
From:   Pali Rohár <pali@...nel.org>
To:     "Guilherme G. Piccoli" <gpiccoli@...lia.com>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Guowen Shan <gshan@...hat.com>,
        Tyrel Datwyler <tyreld@...ux.ibm.com>,
        linuxppc-dev@...ts.ozlabs.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/2] powerpc/pci: Add config option for using OF 'reg'
 for PCI domain

On Friday 15 July 2022 11:55:04 Guilherme G. Piccoli wrote:
> On 06/07/2022 07:21, Pali Rohár wrote:
> > [...] 
> > Fix this issue and introduce a new option CONFIG_PPC_PCI_DOMAIN_FROM_OF_REG.
> > When this option is disabled then powerpc kernel would assign PCI domains
> > in the similar way like it is doing kernel for other architectures,
> > starting from zero and also how it was done prior that commit.
> 
> I found this sentence a bit weird, "in the similar way like it is doing
> kernel for other architectures", but other than that:

If you have some idea how to improve commit description, let me know and
I can change it.

> Reviewed-by: Guilherme G. Piccoli <gpiccoli@...lia.com>
> 
> Thanks for the improvement!
> Cheers,
> 
> 
> Guilherme
> 
> 
> > 
> > This option is by default enabled for powernv and pseries platform for which
> > was that commit originally intended.
> > 
> > With this change upgrading kernels from LTS 4.4 version does not change PCI
> > domain on smaller embedded platforms with fixed number of PCIe controllers.
> > And also ensure that PCI domain zero is present as before that commit.
> > 
> > Fixes: 63a72284b159 ("powerpc/pci: Assign fixed PHB number based on device-tree properties")
> > Signed-off-by: Pali Rohár <pali@...nel.org>
> > ---
> > Changes in v2:
> > * Enable CONFIG_PPC_PCI_DOMAIN_FROM_OF_REG by default on powernv and pseries
> > ---
> >  arch/powerpc/Kconfig             | 11 +++++++++++
> >  arch/powerpc/kernel/pci-common.c |  4 ++--
> >  2 files changed, 13 insertions(+), 2 deletions(-)
> > 
> > diff --git a/arch/powerpc/Kconfig b/arch/powerpc/Kconfig
> > index f66084bc1dfe..053a88e84049 100644
> > --- a/arch/powerpc/Kconfig
> > +++ b/arch/powerpc/Kconfig
> > @@ -386,6 +386,17 @@ config PPC_OF_PLATFORM_PCI
> >  	depends on PCI
> >  	depends on PPC64 # not supported on 32 bits yet
> >  
> > +config PPC_PCI_DOMAIN_FROM_OF_REG
> > +	bool "Use OF reg property for PCI domain"
> > +	depends on PCI
> > +	default y if PPC_PSERIES || PPC_POWERNV
> > +	help
> > +	  By default PCI domain for host bridge during its registration is
> > +	  chosen as the lowest unused PCI domain number.
> > +
> > +	  When this option is enabled then PCI domain can be determined
> > +	  also from lower bits of the OF / Device Tree 'reg' property.
> > +
> >  config ARCH_SUPPORTS_UPROBES
> >  	def_bool y
> >  
> > diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> > index 068410cd54a3..7f959df34833 100644
> > --- a/arch/powerpc/kernel/pci-common.c
> > +++ b/arch/powerpc/kernel/pci-common.c
> > @@ -74,7 +74,6 @@ void __init set_pci_dma_ops(const struct dma_map_ops *dma_ops)
> >  static int get_phb_number(struct device_node *dn)
> >  {
> >  	int ret, phb_id = -1;
> > -	u32 prop_32;
> >  	u64 prop;
> >  
> >  	/*
> > @@ -83,7 +82,8 @@ static int get_phb_number(struct device_node *dn)
> >  	 * reading "ibm,opal-phbid", only present in OPAL environment.
> >  	 */
> >  	ret = of_property_read_u64(dn, "ibm,opal-phbid", &prop);
> > -	if (ret) {
> > +	if (ret && IS_ENABLED(CONFIG_PPC_PCI_DOMAIN_FROM_OF_REG)) {
> > +		u32 prop_32;
> >  		ret = of_property_read_u32_index(dn, "reg", 1, &prop_32);
> >  		prop = prop_32;
> >  	}