Re: [PATCH v3 2/3] checks: Add bus checks for simple-bus buses

[David Gibson <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org>]

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On Tue, Mar 07, 2017 at 07:51:15AM -0600, Rob Herring wrote:
> On Mon, Mar 6, 2017 at 9:41 PM, David Gibson
> <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> > On Mon, Mar 06, 2017 at 04:48:18AM -0600, Rob Herring wrote:
> >> On Thu, Mar 2, 2017 at 8:12 PM, David Gibson
> >> <david-xT8FGy+AXnRB3Ne2BGzF6laj5H9X9Tb+@public.gmane.org> wrote:
> >> > On Tue, Feb 28, 2017 at 04:43:09PM -0600, Rob Herring wrote:
> >> >> Add checks to identify simple-bus bus types and checks for child
> >> >> devices. Simple-bus type is generally identified by "simple-bus"
> >> >> compatible string. We also treat the root as a simple-bus, but only for
> >> >> child nodes with reg property.
> >> >>
> >> >> Signed-off-by: Rob Herring <robh-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> >> >> ---
> >> >> v2:
> >> >> - new patch
> >> >>
> >> >>  checks.c | 69 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >> >>  1 file changed, 69 insertions(+)
> >> >>
> >> >> diff --git a/checks.c b/checks.c
> >> >> index 5ed91ac50a10..c4865b4c8da0 100644
> >> >> --- a/checks.c
> >> >> +++ b/checks.c
> >> >> @@ -817,6 +817,72 @@ static void check_pci_device_reg(struct check *c, struct dt_info *dti, struct no
> >> >>  }
> >> >>  WARNING(pci_device_reg, check_pci_device_reg, NULL, &reg_format);
> >> >>
> >> >> +static const struct bus_type simple_bus = {
> >> >> +     .name = "simple-bus",
> >> >> +};
> >> >> +
> >> >> +static bool node_is_compatible(struct node *node, const char *compat)
> >> >> +{
> >> >> +     struct property *prop;
> >> >> +     const char *str;
> >> >> +
> >> >> +     prop = get_property(node, "compatible");
> >> >> +     if (!prop)
> >> >> +             return false;
> >> >> +
> >> >> +     for (str = prop->val.val; str < prop->val.val + prop->val.len; str += strlen(str) + 1) {
> >> >
> >> > This isn't safe if the compatible property is filled with garbage (not
> >> > '\0' terminated) - the strlen() could access beyond the end of the
> >> > property value.
> >>
> >> Okay, I guess I can check that prop->val.val[prop->val.len - 1] == 0 up front.
> >
> > Sure.  Or use strnlen.
> 
> Duh...
> 
> >> >> +             if (streq(str, compat))
> >> >> +                     return true;
> >> >> +     }
> >> >> +     return false;
> >> >> +}
> >> >> +
> >> >> +static void check_simple_bus_bridge(struct check *c, struct dt_info *dti, struct node *node)
> >> >> +{
> >> >> +     if (node_is_compatible(node, "simple-bus") || !node->parent)
> >> >> +             node->bus = &simple_bus;
> >> >
> >> > I don't think it's correct to assume the root bus is always a
> >> > simple-bus.  If it is, it really should be listed explicitly in the
> >> > root node's compatible property.
> >>
> >> It is in the sense that Linux treats the root the same and creates
> >> devices for top level children and then descends for nodes with
> >> "simple-bus".
> >
> > Hmm.. where in Linux is that?  I think that's a bug, technically
> > speaking, traversing the root node's children without regard to the
> > type of the root node.
> 
> drivers/of/platform.c:of_platform_populate() which is called on the
> root node with "simple-bus" in the match table.

It's called on the root node *by platform code*.  And the platform is
selected on properties of the root node, so it already knows something
about what format the root node should have on that particular
platform.  dtc does not know that.

> Plus I know we have some DT's like Tegra that didn't put all their
> devices under a bus (but should have). Maybe I should warn on that
> (i.e. warn on having unit-addresses without a bus type set on root).

There's nothing inherently wrong with having devices on the root bus.
Really platforms that want this should be putting something like:
	compatible = "vendor,myboard", "simple-bus";

in their root node.	

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
http://www.ozlabs.org/~dgibson

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