Re: [PATCH v4] PCI: Unify ECAM constants in native PCI Express drivers

[Florian Fainelli <f.fainelli@gmail.com>]

On 10/4/2020 5:38 PM, Krzysztof Wilczyński wrote:
> Unify ECAM-related constants into a single set of standard constants
> defining memory address shift values for the byte-level address that can
> be used when accessing the PCI Express Configuration Space, and then
> move native PCI Express controller drivers to use newly introduced
> definitions retiring any driver-specific ones.
> 
> The ECAM ("Enhanced Configuration Access Mechanism") is defined by the
> PCI Express specification (see PCI Express Base Specification, Revision
> 5.0, Version 1.0, Section 7.2.2, p. 676), thus most hardware should
> implement it the same way.  Most of the native PCI Express controller
> drivers define their ECAM-related constants, many of these could be
> shared, or use open-coded values when setting the .bus_shift field of
> the struct pci_ecam_ops.
> 
> All of the newly added constants should remove ambiguity and reduce the
> number of open-coded values, and also correlate more strongly with the
> descriptions in the aforementioned specification (see Table 7-1
> "Enhanced Configuration Address Mapping", p. 677).
> 
> There is no change to functionality.
> 
> Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
> Signed-off-by: Krzysztof Wilczyński <kw@linux.com>
> ---

[snip]

>   
> -/* Configuration space read/write support */
> -static inline int brcm_pcie_cfg_index(int busnr, int devfn, int reg)
> -{
> -	return ((PCI_SLOT(devfn) & 0x1f) << PCIE_EXT_SLOT_SHIFT)
> -		| ((PCI_FUNC(devfn) & 0x07) << PCIE_EXT_FUNC_SHIFT)
> -		| (busnr << PCIE_EXT_BUSNUM_SHIFT)
> -		| (reg & ~3);
> -}
> -
>   static void __iomem *brcm_pcie_map_conf(struct pci_bus *bus, unsigned int devfn,
>   					int where)
>   {
> @@ -590,7 +578,7 @@ static void __iomem *brcm_pcie_map_conf(struct pci_bus *bus, unsigned int devfn,
>   		return PCI_SLOT(devfn) ? NULL : base + where;
>   
>   	/* For devices, write to the config space index register */
> -	idx = brcm_pcie_cfg_index(bus->number, devfn, 0);
> +	idx = PCIE_ECAM_BUS(bus->number) | PCIE_ECAM_DEVFN(devfn);

This appears to be correct, so:

Acked-by: Florian Fainelli <f.fainelli@gmail.com>

however, I would have defined a couple of additional helper macros and do:

	idx = PCIE_ECAM_BUS(bus->number) | PCIE_ECAM_DEV(devfn) | 
PCIE_ECAM_FUN(devfn);

for clarity.

[snip]

> +/*
> + * Memory address shift values for the byte-level address that
> + * can be used when accessing the PCI Express Configuration Space.
> + */
> +
> +/*
> + * Enhanced Configuration Access Mechanism (ECAM)
> + *
> + * See PCI Express Base Specification, Revision 5.0, Version 1.0,
> + * Section 7.2.2, Table 7-1, p. 677.
> + */
> +#define PCIE_ECAM_BUS_SHIFT	20 /* Bus Number */
> +#define PCIE_ECAM_DEV_SHIFT	15 /* Device Number */
> +#define PCIE_ECAM_FUN_SHIFT	12 /* Function Number */
> +
> +#define PCIE_ECAM_BUS(x)	(((x) & 0xff) << PCIE_ECAM_BUS_SHIFT)
> +#define PCIE_ECAM_DEVFN(x)	(((x) & 0xff) << PCIE_ECAM_FUN_SHIFT)

For instance, adding these two:

#define PCIE_ECAM_DEV(x)		(((x) & 0x1f) << PCIE_ECAM_DEV_SHIFT)
#define PCIE_ECAM_FUN(x)		(((x) & 0x7) << PCIE_ECAM_FUN_SHIFT)

may be clearer for use in drivers like pcie-brcmstb.c that used to treat 
the device function in terms of device and function (though it was 
called slot there).
-- 
Florian

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