From: David Gibson <david@gibson.dropbear.id.au>
To: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: Yves-Alexis Perez <corsac@debian.org>,
devicetree-compiler@vger.kernel.org, entwicklung@pengutronix.de
Subject: Re: [PATCH v2] libfdt: overlay: ensure that existing phandles are not overwritten
Date: Thu, 22 Feb 2024 20:02:45 +1100 [thread overview]
Message-ID: <ZdcNtSCopy-9BXb0@zatzit> (raw)
In-Reply-To: <eirdh4rp5zcees3b6p7jeazmg323vf74i5cgz64jzeph2bm5mp@qiqpdtz6id4a>
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On Thu, Feb 22, 2024 at 08:22:48AM +0100, Uwe Kleine-König wrote:
> Hello David,
>
> On Thu, Feb 22, 2024 at 05:32:10PM +1100, David Gibson wrote:
> > On Fri, Feb 16, 2024 at 07:19:20PM +0100, Uwe Kleine-König wrote:
> > > [...]
> > > diff --git a/libfdt/fdt_overlay.c b/libfdt/fdt_overlay.c
> > > index 5c0c3981b89d..914acc5b14a6 100644
> > > --- a/libfdt/fdt_overlay.c
> > > +++ b/libfdt/fdt_overlay.c
> > > @@ -520,6 +520,228 @@ static int overlay_fixup_phandles(void *fdt, void *fdto)
> > > return 0;
> > > }
> > >
> >
> > All of these new functions could do with descriptive comments saying
> > what they do (see the existing code for examples).
>
> Yeah, I was lazy. I didn't expect this patch to go in without comments
> and avoided investing time documenting functions that maybe will change
> in the course of the review-resend loop. :-)
>
> > > [...]
> > > +static int overlay_update_node_conflicting_references(void *fdto, int tree_node,
> > > + int fixup_node,
> > > + uint32_t fdt_phandle,
> > > + uint32_t fdto_phandle)
> > > +{
> > > + int fixup_prop;
> > > + int fixup_child;
> > > + int ret;
> > > +
> > > + fdt_for_each_property_offset(fixup_prop, fdto, fixup_node) {
> > > +
> >
> > Extraneous blank line.
> >
> > > + const fdt32_t *fixup_val;
> > > + const char *tree_val;
> >
> > libfdt style is to use tab indents, looks like most of this block has
> > space indents instead.
>
> Huh, I'm surprised about myself that I didn't notice this alone.
>
> > > +
> > > + /*
> > > + * phandles to fixup can be unaligned.
> > > + *
> > > + * Use a memcpy for the architectures that do
> > > + * not support unaligned accesses.
> > > + */
> > > + memcpy(&adj_val, tree_val + poffset, sizeof(adj_val));
> >
> > And here you can use fdt32_ld() which has unaligned access handling
> > built in.
>
> I copied this from somewhere, so I guess there is some potential for
> improvement in existing code. Will take a look.
>
> > > [...]
> > > +
> > > +static int overlay_prevent_phandle_overwrite_node(void *fdt, int fdtnode,
> > > + void *fdto, int fdtonode)
> >
> > Maybe "overlay_resolve_phandle_conflict()" for a slightly shorter
> > function name.
>
> Sounds good, wasn't too lucky with
> overlay_prevent_phandle_overwrite_node() either.
>
> > > +{
> > > + uint32_t fdt_phandle, fdto_phandle;
> > > + int fdtochild;
> > > +
> > > + fdt_phandle = fdt_get_phandle(fdt, fdtnode);
> > > + fdto_phandle = fdt_get_phandle(fdto, fdtonode);
> > > +
> > > + if (fdt_phandle && fdto_phandle) {
> > > + int ret;
> > > +
> > > + ret = overlay_adjust_local_conflicting_phandle(fdto,
> > > + fdt_phandle,
> > > + fdto_phandle);
> > > + if (ret)
> > > + return ret;
> >
> > So while, as you've seen, there can be conflicting phandles between
> > the fdt and the fdto, within the fdto a particular phandle should only
> > appear on a single node. If a phandle is duplicated across nodes
> > witin a single fdto, you have bigger problems. Therefore, having
> > found a conflict, you're already found the only place you need to
> > change the phandle property itself - you don't need to scan the full
> > fdto again.
> >
> > So I believe you can replace the above call with just setting the
> > phandle property on fdtonode.
>
> Oh right!
>
> > > [...]
> > > /**
> > > * overlay_apply_node - Merges a node into the base device tree
> > > * @fdt: Base Device Tree blob
> > > @@ -824,18 +1046,26 @@ int fdt_overlay_apply(void *fdt, void *fdto)
> > > if (ret)
> > > goto err;
> > >
> > > + /* Increase all phandles in the fdto by delta */
> > > ret = overlay_adjust_local_phandles(fdto, delta);
> > > if (ret)
> > > goto err;
> > >
> > > + /* Adapt the phandle values in fdto to the above increase */
> > > ret = overlay_update_local_references(fdto, delta);
> > > if (ret)
> > > goto err;
> > >
> > > + /* Update fdto's phandles using symbols from fdt */
> > > ret = overlay_fixup_phandles(fdt, fdto);
> > > if (ret)
> > > goto err;
> > >
> > > + /* Don't overwrite phandles in fdt */
> > > + ret = overlay_prevent_phandle_overwrite(fdt, fdto);
> > > + if (ret)
> > > + goto err;
> >
> > I think this should go above overlay_fixup_phandles(), so that we're
> > completing all the __local_fixups__ based adjustments before going to
> > the __fixups__ based adjustments.
>
> This is only to please the reader, right? Or is there a corner case I
> failed to see?
Correct. At least as far as I've seen, too.
> The feedback I removed in this mail I agree with. Expect a v3 soon.
>
> Thanks for your time to review my patch,
> Uwe
>
--
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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next prev parent reply other threads:[~2024-02-22 9:02 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-02-16 18:19 [PATCH v2] libfdt: overlay: ensure that existing phandles are not overwritten Uwe Kleine-König
2024-02-16 21:06 ` Uwe Kleine-König
2024-02-22 6:33 ` David Gibson
2024-02-22 6:32 ` David Gibson
2024-02-22 7:22 ` Uwe Kleine-König
2024-02-22 9:02 ` David Gibson [this message]
2024-02-22 9:38 ` Uwe Kleine-König
2024-02-23 4:41 ` David Gibson
2024-02-23 7:53 ` Uwe Kleine-König
2024-02-23 8:15 ` David Gibson
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