On Mon, 9 May 2011, Jan Andersson wrote:
> This patch adds support for big endian mmio to the UHCI HCD. Big endian
> mmio is supported by adding a flag bit to the UHCI HCD replicating the
> solution used in the EHCI HCD.
>
> When adding big endian support this patch also adds a check to see if we
> need to support HCs with PCI I/O registers when we support HCs with MMIO.
>
> This patch also adds 'const' to the register access functions' uhci_hcd
> argument.
>
> Signed-off-by: Jan Andersson <jan@xxxxxxxxxxx>
> diff --git a/drivers/usb/host/uhci-hcd.h b/drivers/usb/host/uhci-hcd.h
> index a4e64d0..31f110f 100644
> --- a/drivers/usb/host/uhci-hcd.h
> +++ b/drivers/usb/host/uhci-hcd.h
...
> +#if defined(CONFIG_USB_UHCI_BIG_ENDIAN_MMIO)
Isn't "#ifdef" more common?
> +/* Support (non-PCI) big endian host controllers */
> +#define uhci_big_endian_mmio(u) ((u)->big_endian_mmio)
> +#else
> +#define uhci_big_endian_mmio(u) 0
> +#endif
>
> -static inline u32 uhci_readl(struct uhci_hcd *uhci, int reg)
> +static inline u32 uhci_readl(const struct uhci_hcd *uhci, int reg)
> {
> if (uhci_has_pci_registers(uhci))
> return inl(uhci->io_addr + reg);
> +#if defined(CONFIG_USB_UHCI_BIG_ENDIAN_MMIO)
> + else if (uhci_big_endian_mmio(uhci))
> + return readl_be(uhci->regs + reg);
> +#endif
> else
> return readl(uhci->regs + reg);
> }
I have to admit, this whole business is kind of confusing. The same is
true of the implementation in ehci.h (obviously, since this is more or
less a direct copy).
In principle, the device can use either big- or little-endian mmio, and
the CPU can be either big- or little-endian. If the two agree then no
change should be needed, otherwise the values should have to be
byte-swapped. But that doesn't appear to be what this code does.
Probably I'm just misunderstanding something.
Alan Stern
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
