On Sun, 01 Mar 2015 17:23:11 -0500
, Peter Hurley <peter@xxxxxxxxxxxxxxxxxx>
wrote:
> Hi Kevin,
>
> On 11/24/2014 06:36 PM, Kevin Cernekee wrote:
> > If an earlycon (stdout-path) node is being used, check for "big-endian"
> > or "native-endian" properties and pass the appropriate iotype to the
> > driver.
> >
> > Note that LE sets UPIO_MEM (8-bit) but BE sets UPIO_MEM32BE (32-bit). The
> > big-endian property only really makes sense in the context of 32-bit
> > registers, since 8-bit accesses never require data swapping.
> >
> > At some point, the of_earlycon code may want to pass in the reg-io-width,
> > reg-offset, and reg-shift parameters too.
> >
> > Signed-off-by: Kevin Cernekee <cernekee@xxxxxxxxx>
> > ---
> > drivers/of/fdt.c | 7 ++++++-
> > drivers/tty/serial/earlycon.c | 4 ++--
> > include/linux/serial_core.h | 2 +-
> > 3 files changed, 9 insertions(+), 4 deletions(-)
> >
> > diff --git a/drivers/of/fdt.c b/drivers/of/fdt.c
> > index 658656f..9d21472 100644
> > --- a/drivers/of/fdt.c
> > +++ b/drivers/of/fdt.c
> > @@ -794,6 +794,8 @@ int __init early_init_dt_scan_chosen_serial(void)
> >
> > while (match->compatible[0]) {
> > unsigned long addr;
> > + unsigned char iotype = UPIO_MEM;
> > +
> > if (fdt_node_check_compatible(fdt, offset, match->compatible)) {
> > match++;
> > continue;
> > @@ -803,7 +805,10 @@ int __init early_init_dt_scan_chosen_serial(void)
> > if (!addr)
> > return -ENXIO;
> >
> > - of_setup_earlycon(addr, match->data);
> > + if (of_fdt_is_big_endian(fdt, offset))
> > + iotype = UPIO_MEM32BE;
> > +
> > + of_setup_earlycon(addr, iotype, match->data);
>
> I know these got ACKs already but as you point out in the commit log,
> earlycon _will_ need reg-io-width, reg-offset and reg-shift. Since the
> distinction between early_init_dt_scan_chosen_serial() and
> of_setup_earlycon() is arbitrary, I'd rather see of_setup_earlycon()
> taught to properly decode of_serial driver bindings instead of a
> stack of parameters to of_setup_earlycon().
>
> In fact, this patch allows a mis-defined devicetree to bring up a
> functioning earlycon because the 'big-endian' property is directly
> associated with UPIO_MEM32BE, which will create incompatibility problems
> when DT earlycon is fixed to decode the of_serial DT bindings.
That's a good point. This hasn't been merged yet, so there isn't any
impact on addressing this. I would propose that for consistency, the
earlycon code should always default to 8-bit access. if big-endian
accesses are required, then reg-io-width + big-endian must be specified.
Something like the following would do it and would be future-proof. We
can add support for 16 or 64bit big or little endian access if it ever
became necessary.
static int of_flat_dt_get_iotype(unsigned long node)
{
int size, width = 1;
__be32 *prop;
bool bigendian = false;
if (of_get_flat_dt_prop(node, "big-endian", NULL));
bigendian = true;
prop = of_get_flat_dt_prop(node, "reg-io-width", &size);
if (prop) {
if (size != sizeof(u32))
return -EINVAL;
width = fdt32_to_cpu(*prop);
}
switch (width) {
case 1:
return UPIO_MEM; /* big-endian flag has no effect */
case 4:
return bigendian ? UPIO_MEM32BE : UPIO_MEM32;
default:
return -EINVAL;
}
}
...
iotype = of_fdt_get_iotype(fdt, offset);
if (iotype == UPIO_INVAL)
/*fail*/
g.
