On Wed, 12 Nov 2014 12:54:02 -0800
, Kevin Cernekee <cernekee@xxxxxxxxx>
wrote:
> SoC peripherals can come in several different flavors:
>
> - little-endian: registers always need to be accessed in LE mode (so the
> kernel should perform a swap if the CPU is running BE)
>
> - big-endian: registers always need to be accessed in BE mode (so the
> kernel should perform a swap if the CPU is running LE)
>
> - native-endian: the bus will automatically swap accesses, so the kernel
> should never swap
> Introduce a function that checks an OF device node to see whether it
> contains a "big-endian" or "native-endian" property. For the former case,
> always return true. For the latter case, return true iff the kernel was
> built for BE (implying that the BE MMIO accessors do not perform a swap).
> Otherwise return false, assuming LE registers.
>
> LE registers are assumed by default because most existing drivers (libahci,
> serial8250, usb) always use readl/writel in the absence of instructions
> to the contrary, so that will be our fallback.
This is proposing a new binding, or at least a common pattern to be used
by other bindings. It should be documented under
Documentation/devicetree/bindings/. I suggest creating a new file under
bindings/common-properties.txt
Otherwise looks fine to me. We'll give it a week to see if there are any
other comments, but I think this looks fine.
g.
>
> Signed-off-by: Kevin Cernekee <cernekee@xxxxxxxxx>
> ---
> drivers/of/base.c | 23 +++++++++++++++++++++++
> include/linux/of.h | 6 ++++++
> 2 files changed, 29 insertions(+)
>
> diff --git a/drivers/of/base.c b/drivers/of/base.c
> index 81c095f..35d95a1 100644
> --- a/drivers/of/base.c
> +++ b/drivers/of/base.c
> @@ -552,6 +552,29 @@ bool of_device_is_available(const struct device_node *device)
> EXPORT_SYMBOL(of_device_is_available);
>
> /**
> + * of_device_is_big_endian - check if a device has BE registers
> + *
> + * @device: Node to check for endianness
> + *
> + * Returns true if the device has a "big-endian" property, or if the kernel
> + * was compiled for BE *and* the device has a "native-endian" property.
> + * Returns false otherwise.
> + *
> + * Callers would nominally use ioread32be/iowrite32be if
> + * of_device_is_big_endian() == true, or readl/writel otherwise.
> + */
> +bool of_device_is_big_endian(const struct device_node *device)
> +{
> + if (of_property_read_bool(device, "big-endian"))
> + return true;
> + if (IS_ENABLED(CONFIG_CPU_BIG_ENDIAN) &&
> + of_property_read_bool(device, "native-endian"))
> + return true;
> + return false;
> +}
> +EXPORT_SYMBOL(of_device_is_big_endian);
> +
> +/**
> * of_get_parent - Get a node's parent if any
> * @node: Node to get parent
> *
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 7aaaa59..fc70b01 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -276,6 +276,7 @@ extern int of_property_read_string_helper(struct device_node *np,
> extern int of_device_is_compatible(const struct device_node *device,
> const char *);
> extern bool of_device_is_available(const struct device_node *device);
> +extern bool of_device_is_big_endian(const struct device_node *device);
> extern const void *of_get_property(const struct device_node *node,
> const char *name,
> int *lenp);
> @@ -431,6 +432,11 @@ static inline bool of_device_is_available(const struct device_node *device)
> return false;
> }
>
> +static inline bool of_device_is_big_endian(const struct device_node *device)
> +{
> + return false;
> +}
> +
> static inline struct property *of_find_property(const struct device_node *np,
> const char *name,
> int *lenp)
> --
> 2.1.1
>
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