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: <17fb8d12-60f9-09d5-91fa-09d5a5a9a4fd@igalia.com>
Date:   Fri, 15 Jul 2022 11:55:04 -0300
From:   "Guilherme G. Piccoli" <gpiccoli@...lia.com>
To:     Pali Rohár <pali@...nel.org>,
        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>
Cc:     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 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:

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;
>  	}