linux-kernel - Re: [PATCH] PCI: Generic Configuration Access Mechanism support

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Date:	Mon, 19 May 2014 19:03:04 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	Srikanth Thokala <sthokal@...inx.com>
Cc:	bhelgaas@...gle.com, will.deacon@....com, michals@...inx.com,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org
Subject: Re: [PATCH] PCI: Generic Configuration Access Mechanism support

On Sunday 18 May 2014 19:38:45 Srikanth Thokala wrote:
> +
> +	if (cfg->ops->is_valid_cfg_access) {
> +		if (!cfg->ops->is_valid_cfg_access(bus, devfn)) {
> +			*val = PCI_CFG_INVALID_DEVFN;
> +			return PCIBIOS_DEVICE_NOT_FOUND;
> +		}
> +	}

Can you explain why this callback is needed? If the space for the
bus is mapped, any access should just work.

> +
> +/* Generic PCI CAM/ECAM Configuration Bus Operations */
> +
> +struct pci_cfg_bus_ops pci_cfg_cam_bus_ops = {
> +	.bus_shift	= PCI_CFG_CAM_BUS_NUM,
> +	.map_bus	= pci_cfg_map_bus_cam,
> +};
> +EXPORT_SYMBOL_GPL(pci_cfg_cam_bus_ops);
> +
> +struct pci_cfg_bus_ops pci_cfg_ecam_bus_ops = {
> +	.bus_shift	= PCI_CFG_ECAM_BUS_NUM,
> +	.map_bus	= pci_cfg_map_bus_ecam,
> +};
> +EXPORT_SYMBOL_GPL(pci_cfg_ecam_bus_ops);
> +
> +struct pci_ops pci_cfg_ops = {
> +	.read	= pci_cfg_read,
> +	.write	= pci_cfg_write,
> +};
> +EXPORT_SYMBOL_GPL(pci_cfg_ops);


If we can find a way to remove the is_valid_cfg_access() check, we're
probably better off removing the cfg_bus_ops as well, and exporting
two sets of pci_ops. There will be a little more duplication here, but
also less complexity in this module, and more importantly in the drivers
using it.

	Arnd
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