linux-kernel - Re: [PATCH RFC] gpiolib: ensure that fwnode is properly set

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Date:   Wed, 16 Nov 2022 11:35:37 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Brian Masney <bmasney@...hat.com>
Cc:     linus.walleij@...aro.org, brgl@...ev.pl,
        linux-gpio@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, psodagud@...cinc.com,
        quic_shazhuss@...cinc.com, quic_ppareek@...cinc.com,
        ahalaney@...hat.com, echanude@...hat.com,
        nicolas.dechesne@...aro.org
Subject: Re: [PATCH RFC] gpiolib: ensure that fwnode is properly set

On Wed, Nov 16, 2022 at 11:21:37AM +0100, Thierry Reding wrote:
> On Mon, Nov 14, 2022 at 03:29:43PM -0500, Brian Masney wrote:
> > Note that this is a RFC patch and not meant to be merged. I looked into
> > a problem with linux-next-20221110 on the Qualcomm SA8540P automotive
> > board (sc8280xp) where the UFS host controller would fail to probe due
> > to repeated probe deferrals when trying to get reset-gpios via
> > devm_gpiod_get_optional().
> > 
> > of_get_named_gpiod_flags() returns -EPROBE_DEFER, which is caused by
> > of_gpiochip_match_node_and_xlate() returning 0 since the of_xlate function
> > pointer is not set for the qcom,sc8280xp-tlmm pinctrl driver. The
> > pinctrl driver doesn't define one, so of_gpiochip_add() should
> > automatically setup of_gpio_simple_xlate() on it's behalf. This doesn't
> > happen since the fwnode member on the struct gpiochip is set to null
> > when of_gpiochip_add() is called. Let's work around this by ensuring
> > that it's set if available.
> > 
> > Note that this broke sometime within the last few weeks within
> > linux-next and I haven't bisected this. I'm posting this in the hopes
> > that someone may know offhand which patch(es) may have broken this.
> > 
> > Signed-off-by: Brian Masney <bmasney@...hat.com>
> > ---
> >  drivers/gpio/gpiolib.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> > index 11fb7ec883e9..8bec66008869 100644
> > --- a/drivers/gpio/gpiolib.c
> > +++ b/drivers/gpio/gpiolib.c
> > @@ -678,7 +678,7 @@ int gpiochip_add_data_with_key(struct gpio_chip *gc, void *data,
> >  	 * Assign fwnode depending on the result of the previous calls,
> >  	 * if none of them succeed, assign it to the parent's one.
> >  	 */
> > -	gdev->dev.fwnode = dev_fwnode(&gdev->dev) ?: fwnode;
> > +	gc->fwnode = gdev->dev.fwnode = dev_fwnode(&gdev->dev) ?: fwnode;
> 
> This doesn't look right to me. Looking at the documentation of
> gc->fwnode and how it is used, the purpose of this is to allow
> explicitly overriding the fwnode that the GPIO chip will use.
> 
> So really this should not be used beyond the initial registration
> in gpiochip_add_data_with_key(). If the above patch fixes anything,
> then I suspect somebody is using gc->fwnode outside of this
> registration.
> 
> Looking at gpiolib, the only remaining place that seems to do this is
> the gpio-reserved-ranges handling code, in which case, the below on top
> of my initial patch might fix that. That might explain why MSM is still
> seeing issues.
> 
> --- >8 ---
> diff --git a/drivers/gpio/gpiolib.c b/drivers/gpio/gpiolib.c
> index 11fb7ec883e9..d692ad5c5a27 100644
> --- a/drivers/gpio/gpiolib.c
> +++ b/drivers/gpio/gpiolib.c
> @@ -447,10 +447,11 @@ static unsigned long *gpiochip_allocate_mask(struct gpio_chip *gc)
>  
>  static unsigned int gpiochip_count_reserved_ranges(struct gpio_chip *gc)
>  {
> +	struct fwnode_handle *fwnode = dev_fwnode(&gc->gpiodev->dev);
>  	int size;
>  
>  	/* Format is "start, count, ..." */
> -	size = fwnode_property_count_u32(gc->fwnode, "gpio-reserved-ranges");
> +	size = fwnode_property_count_u32(fwnode, "gpio-reserved-ranges");
>  	if (size > 0 && size % 2 == 0)
>  		return size;
>  
> @@ -471,6 +472,7 @@ static int gpiochip_alloc_valid_mask(struct gpio_chip *gc)
>  
>  static int gpiochip_apply_reserved_ranges(struct gpio_chip *gc)
>  {
> +	struct fwnode_handle *fwnode = dev_fwnode(&gc->gpiodev->dev);
>  	unsigned int size;
>  	u32 *ranges;
>  	int ret;
> @@ -483,7 +485,7 @@ static int gpiochip_apply_reserved_ranges(struct gpio_chip *gc)
>  	if (!ranges)
>  		return -ENOMEM;
>  
> -	ret = fwnode_property_read_u32_array(gc->fwnode, "gpio-reserved-ranges", ranges, size);
> +	ret = fwnode_property_read_u32_array(fwnode, "gpio-reserved-ranges", ranges, size);
>  	if (ret) {
>  		kfree(ranges);
>  		return ret;
> --- >8 ---
> 
> I don't have a good idea about the Lenovo X13 issue, though, but I
> haven't looked at ACPI at all since I don't have any hardware to test
> on.

Ah... looks like that device was actually a Thinkpad X13*s*, which is
based on a Qualcomm chip, so maybe this patch fixes that one, too. It
does use gpio-reserved-ranges, so seems at least likely.

Thierry

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