linux-kernel - Re: [PATCH v2] of: restore old handling of cells_name=NULL in of_*_phandle_with

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Message-ID: <20190919133242.GA27990@bogus>
Date:   Thu, 19 Sep 2019 08:32:42 -0500
From:   Rob Herring <robh@...nel.org>
To:     Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>
Cc:     Peter Rosin <peda@...ntia.se>,
        Frank Rowand <frowand.list@...il.com>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-mediatek@...ts.infradead.org" 
        <linux-mediatek@...ts.infradead.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        Matthias Brugger <matthias.bgg@...il.com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Geert Uytterhoeven <geert+renesas@...der.be>
Subject: Re: [PATCH v2] of: restore old handling of cells_name=NULL in
  of_*_phandle_with_args()

On Wed, 18 Sep 2019 10:47:48 +0200, Uwe =?iso-8859-1?Q?Kleine-K=F6nig?=          wrote:
> Before commit e42ee61017f5 ("of: Let of_for_each_phandle fallback to
> non-negative cell_count") the iterator functions calling
> of_for_each_phandle assumed a cell count of 0 if cells_name was NULL.
> This corner case was missed when implementing the fallback logic in
> e42ee61017f5 and resulted in an endless loop.
> 
> Restore the old behaviour of of_count_phandle_with_args() and
> of_parse_phandle_with_args() and add a check to
> of_phandle_iterator_init() to prevent a similar failure as a safety
> precaution. of_parse_phandle_with_args_map() doesn't need a similar fix
> as cells_name isn't NULL there.
> 
> Affected drivers are:
>  - drivers/base/power/domain.c
>  - drivers/base/power/domain.c
>  - drivers/clk/ti/clk-dra7-atl.c
>  - drivers/hwmon/ibmpowernv.c
>  - drivers/i2c/muxes/i2c-demux-pinctrl.c
>  - drivers/iommu/mtk_iommu.c
>  - drivers/net/ethernet/freescale/fman/mac.c
>  - drivers/opp/of.c
>  - drivers/perf/arm_dsu_pmu.c
>  - drivers/regulator/of_regulator.c
>  - drivers/remoteproc/imx_rproc.c
>  - drivers/soc/rockchip/pm_domains.c
>  - sound/soc/fsl/imx-audmix.c
>  - sound/soc/fsl/imx-audmix.c
>  - sound/soc/meson/axg-card.c
>  - sound/soc/samsung/tm2_wm5110.c
>  - sound/soc/samsung/tm2_wm5110.c
> 
> Thanks to Geert Uytterhoeven for reporting the issue, Peter Rosin for
> helping pinpoint the actual problem and the testers for confirming this
> fix.
> 
> Fixes: e42ee61017f5 ("of: Let of_for_each_phandle fallback to non-negative cell_count")
> Tested-by: Marek Szyprowski <m.szyprowski@...sung.com>
> Tested-by: Geert Uytterhoeven <geert+renesas@...der.be>
> Signed-off-by: Uwe Kleine-König <u.kleine-koenig@...gutronix.de>
> ---
> 
> On Wed, Sep 18, 2019 at 08:01:05AM +0000, Peter Rosin wrote:
> > On 2019-09-18 08:38, Uwe Kleine-König wrote:
> > >  EXPORT_SYMBOL(of_parse_phandle_with_args);
> > >  
> > > @@ -1765,6 +1779,18 @@ int of_count_phandle_with_args(const struct device_node *np, const char *list_na
> > >  	struct of_phandle_iterator it;
> > >  	int rc, cur_index = 0;
> > >  
> > > +	/* If cells_name is NULL we assume a cell count of 0 */
> > > +	if (cells_name == NULL) {
> > 
> > A couple of nits.
> > 
> > I don't know if there are other considerations, but in the previous two
> > hunks you use !cells_name instead of comparing explicitly with NULL.
> > Personally, I find the shorter form more readable, and in the name of
> > consistency bla bla...
> 
> Ack, changed to !cells_name here, too.
> 
> > 
> > Also, the comment explaining this NULL-check didn't really make sense
> > to me until I realized that knowing the cell count to be zero makes
> > counting trivial. Something along those lines should perhaps be in the
> > comment?
> 
> You're right, I extended the comment a bit.
>  
> > But as I said, these are nits. Feel free to ignore.
> 
> I considered resending already anyhow as I fatfingerd my email address.
> this is fixed now, too. Additionally I fixed a typo in one of the
> comments.
> 
> Thanks for your feedback.
> 
> Best regards
> Uwe
> 
>  drivers/of/base.c | 35 +++++++++++++++++++++++++++++++++--
>  1 file changed, 33 insertions(+), 2 deletions(-)
> 

Applied, thanks.

Rob