Re: [RFC PATCH kernel] powerpc/pci: Get rid of unused @parent pointer in pci_controller

[Benjamin Herrenschmidt <benh@kernel.crashing.org>]

On Mon, 2017-11-06 at 14:24 +1100, Alexey Kardashevskiy wrote:
> The @parent pointer is supposed to point to a device which represents
> a PCI controller, however it is never set to anything and remains NULL;
> it is also quite common to pass NULL to pci_create_root_bus().
> 
> Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
> ---

It's used for anything using of_pci_phb_probe() such as Cell.


> 
> This @parent is NULL for every PHB in garrison machines, for example.
> Where would this pointer be really used?
> 
> I wonder how does setting it make any difference in sysfs for CXL vphb?
> 
> In general, I'd think that @parent makes sense and every PHB
> has a parent device struct like any other device and the platform
> code binds a correct device driver to a PHB and we can avoid
> having PNV_PHB_IODA2&co switches but for some reason PHBs are
> hardcoded in the platform code.
> 
> ---
>  arch/powerpc/include/asm/pci-bridge.h | 1 -
>  arch/powerpc/kernel/pci-common.c      | 2 +-
>  drivers/misc/cxl/vphb.c               | 3 ---
>  3 files changed, 1 insertion(+), 5 deletions(-)
> 
> diff --git a/arch/powerpc/include/asm/pci-bridge.h b/arch/powerpc/include/asm/pci-bridge.h
> index 752718a2949d..ad88ddeaa6b7 100644
> --- a/arch/powerpc/include/asm/pci-bridge.h
> +++ b/arch/powerpc/include/asm/pci-bridge.h
> @@ -60,7 +60,6 @@ struct pci_controller {
>  #endif
>  	struct device_node *dn;
>  	struct list_head list_node;
> -	struct device *parent;
>  
>  	int first_busno;
>  	int last_busno;
> diff --git a/arch/powerpc/kernel/pci-common.c b/arch/powerpc/kernel/pci-common.c
> index 02831a396419..597576777c34 100644
> --- a/arch/powerpc/kernel/pci-common.c
> +++ b/arch/powerpc/kernel/pci-common.c
> @@ -1681,7 +1681,7 @@ void pcibios_scan_phb(struct pci_controller *hose)
>  	pci_add_resource(&resources, &hose->busn);
>  
>  	/* Create an empty bus for the toplevel */
> -	bus = pci_create_root_bus(hose->parent, hose->first_busno,
> +	bus = pci_create_root_bus(NULL, hose->first_busno,
>  				  hose->ops, hose, &resources);
>  	if (bus == NULL) {
>  		pr_err("Failed to create bus for PCI domain %04x\n",
> diff --git a/drivers/misc/cxl/vphb.c b/drivers/misc/cxl/vphb.c
> index 512a4897dbf6..ae3fe1563812 100644
> --- a/drivers/misc/cxl/vphb.c
> +++ b/drivers/misc/cxl/vphb.c
> @@ -232,9 +232,6 @@ int cxl_pci_vphb_add(struct cxl_afu *afu)
>  	if (!phb)
>  		return -ENODEV;
>  
> -	/* Setup parent in sysfs */
> -	phb->parent = parent;
> -
>  	/* Setup the PHB using arch provided callback */
>  	phb->ops = &cxl_pcie_pci_ops;
>  	phb->cfg_addr = NULL;