linux-kernel - Re: [PATCH 1/2] clk: Do not register provider with a NULL dev->of

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Date:   Fri, 23 Apr 2021 20:21:59 +0200
From:   nicolas saenz julienne <nsaenz@...nel.org>
To:     Saravana Kannan <saravanak@...gle.com>,
        Tudor Ambarus <tudor.ambarus@...rochip.com>
Cc:     mturquette@...libre.com, sboyd@...nel.org, maxime@...no.tech,
        gregkh@...uxfoundation.org, rafael@...nel.org, khilman@...nel.org,
        ulf.hansson@...aro.org, len.brown@...el.com, pavel@....cz,
        robh+dt@...nel.org, frowand.list@...il.com, maz@...nel.org,
        tglx@...utronix.de, geert@...ux-m68k.org, nsaenzjulienne@...e.de,
        linux@...ck-us.net, guillaume.tucker@...labora.com,
        linux-clk@...r.kernel.org, linux-kernel@...r.kernel.org,
        corbet@....net, nicolas.ferre@...rochip.com,
        claudiu.beznea@...rochip.com, linux-doc@...r.kernel.org,
        linux-pm@...r.kernel.org, devicetree@...r.kernel.org,
        linux-acpi@...r.kernel.org, kernel-team@...roid.com,
        linux-rpi-kernel@...ts.infradead.org,
        Marek Szyprowski <m.szyprowski@...sung.com>
Subject: Re: [PATCH 1/2] clk: Do not register provider with a NULL
 dev->of_node

Hi Saravana, Tudor,

On Fri, 2021-04-23 at 10:24 -0700, Saravana Kannan wrote:
> On Fri, Apr 23, 2021 at 10:14 AM Tudor Ambarus
> <tudor.ambarus@...rochip.com> wrote:
> > 
> > commit 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> > revealed that clk/bcm/clk-raspberrypi.c driver calls
> > devm_of_clk_add_hw_provider(), with a NULL dev->of_node.
> > 
> > devm_of_clk_add_hw_provider() should not register the provider with
> > a NULL dev->of_node, as there is no of_node. Apart of the NULL pointer
> > dereference that will result when calling fwnode_dev_initialized() in
> > of_clk_add_hw_provider(), another problem is that when two drivers calling
> > of_clk_add_hw_provider() with np = NULL, their unregistration order is not
> > guaranteed to be correct. Avoid all the problems and just return -ENODEV
> > when the callers of devm_of_clk_add_hw_provider() use a NULL dev->of_node,
> > which seems the natural way to do.
> > 
> > Reported-by: Marek Szyprowski <m.szyprowski@...sung.com>
> > Fixes: 6579c8d97ad7 ("clk: Mark fwnodes when their clock provider is added")
> > Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
> > ---
> >  drivers/clk/clk.c | 12 +++++++-----
> >  1 file changed, 7 insertions(+), 5 deletions(-)
> > 
> > diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
> > index e2ec1b745243..8b5077cc5e67 100644
> > --- a/drivers/clk/clk.c
> > +++ b/drivers/clk/clk.c
> > @@ -4634,11 +4634,10 @@ static struct device_node *get_clk_provider_node(struct device *dev)
> >   * @get: callback for decoding clk_hw
> >   * @data: context pointer for @get callback
> >   *
> > - * Registers clock provider for given device's node. If the device has no DT
> > - * node or if the device node lacks of clock provider information (#clock-cells)
> > - * then the parent device's node is scanned for this information. If parent node
> > - * has the #clock-cells then it is used in registration. Provider is
> > - * automatically released at device exit.
> > + * Registers clock provider for given device's node. If the device node lacks
> > + * of clock provider information (#clock-cells) then the parent device's node is
> > + * scanned for this information. If parent node has the #clock-cells then it is
> > + * used in registration. Provider is automatically released at device exit.
> >   *
> >   * Return: 0 on success or an errno on failure.
> >   */
> > @@ -4650,6 +4649,9 @@ int devm_of_clk_add_hw_provider(struct device *dev,
> >         struct device_node **ptr, *np;
> >         int ret;
> > 
> > +       if (!dev->of_node)
> > +               return -ENODEV;
> > +
> 
> Based on the other discussions, for now, just return 0. The error
> might cause other issues in other drivers. We can clean this up later.

+1, Let's return 0 and do nothing skip the logic in the driver.

Now, from what I read in devm_of_clk_add_hw_provider(), there is a use case for
entering with '!dev->of_node'. See get_clk_provider_node()'s usage. So I think
we should only bail if that function fails to provide a device_node.

Regards,
Nicolas