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: Fri, 23 Feb 2024 15:41:40 +1100 [thread overview]
Message-ID: <ZdgiBAEvvr731H7c@zatzit> (raw)
In-Reply-To: <oitc63fe3agrg2vwgml6x652uo4dqst3m6kbaiu4rs3sbqnco4@rylqo655o4m5>
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On Thu, Feb 22, 2024 at 10:38:54AM +0100, Uwe Kleine-König wrote:
> 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:
> > > +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) {
> > > +
> > > + const fdt32_t *fixup_val;
> > > + const char *tree_val;
> > > + const char *name;
> > > + int fixup_len;
> > > + int tree_len;
> > > + int i;
> > > +
> > > + fixup_val = fdt_getprop_by_offset(fdto, fixup_prop,
> > > + &name, &fixup_len);
> > > + if (!fixup_val)
> > > + return fixup_len;
> > > +
> > > + if (fixup_len % sizeof(uint32_t))
> > > + return -FDT_ERR_BADOVERLAY;
> > > + fixup_len /= sizeof(uint32_t);
> > > +
> > > + tree_val = fdt_getprop(fdto, tree_node, name, &tree_len);
> > > + if (!tree_val) {
> > > + if (tree_len == -FDT_ERR_NOTFOUND)
> > > + return -FDT_ERR_BADOVERLAY;
> > > +
> > > + return tree_len;
> > > + }
> > > +
> > > + for (i = 0; i < fixup_len; i++) {
> > > + fdt32_t adj_val;
> > > + uint32_t poffset;
> > > +
> > > + poffset = fdt32_to_cpu(fixup_val[i]);
> >
> > You can use fdt32_ld_() here to slightly simplify this
>
> I don't see what you suggest here. fixup_val is assigned to in
> fdt_getprop_by_offset() which I need to get fixup_len and then fixup_val
> is already around. If you still think this could be improved, please be
> more explicit.
poffset = fdt32_ld_(fixup_val + i);
Thus combining the memory read and the byteswap into one operation. I
guess it doesn't really simplify the code, but correctly handling
reads and writes to memory within the dtb is what the fdt*_ld() and
fdt*_st() helpers are for.
> > > +
> > > + /*
> > > + * 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.
Specifically
adj_val = fdt32_ld(tree_val + poffset)
And then replacing fdt32_to_cpu(adj_val) with just adj_val below.
> >
> > > +
> > > + if (fdt32_to_cpu(adj_val) == fdto_phandle) {
> > > +
> > > + adj_val = cpu_to_fdt32(fdt_phandle);
> > > +
> > > + ret = fdt_setprop_inplace_namelen_partial(fdto,
> > > + tree_node,
> > > + name,
> > > + strlen(name),
> > > + poffset,
> > > + &adj_val,
> > > + sizeof(adj_val));
> > > + if (ret == -FDT_ERR_NOSPACE)
> > > + return -FDT_ERR_BADOVERLAY;
> > > +
> > > + if (ret)
> > > + return ret;
> >
> > And here you can use fdt32_st() on (tree_val + poffset), avoiding
> > quite some complexity.
>
> There is some complexity because tree_val is a const char * (as this is
> what fdt_getprop() returns) and fdt32_st() obviously doens't take a
> const pointer.
Ah, right. You can use fdt_getprop_w() to get a writable pointer
instead. If there was a way to have fdt_getprop() return a const
pointer only if the fdt pointer it was given was const, I'd do that.
> If you want to play around with that, the code is mostly a copy of
> overlay_update_local_node_references() which could benefit from your
> suggestions in the same way.
That's quite plausible.
> Can I lure you in improving overlay_update_local_node_references()? Then
Fair point..
https://github.com/dgibson/dtc/commit/24f60011fd43683d8e3916435c4c726e9baac9c9
> I could copy from the improved function for my patch. (Or maybe refactor
> the function to take a function as parameter which is
Eh... I'd prefer to avoid higher order functions in something this low
level.
> uint32_t delta;
> uint32_t increase_by_delta(uint32_t phandle)
> {
> return phandle + delta;
> }
>
> for the overlay_update_local_node_references() case and
>
> uint32_t fdt_phandle;
> uint32_t fdto_phandle;
> uint32_t resolve_fdt_conflict(uint32_t phandle)
> {
> if (phandle == fdto_phandle)
> return fdt_phandle;
> else
> return phandle;
> }
>
> for my function (maybe passing the data stored in global vars here in a
> context parameter).
>
> Best regards
> 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:[~2024-02-23 4:42 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
2024-02-22 9:38 ` Uwe Kleine-König
2024-02-23 4:41 ` David Gibson [this message]
2024-02-23 7:53 ` Uwe Kleine-König
2024-02-23 8:15 ` David Gibson
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