linux-kernel - Re: [PATCH 2/2] pinctrl: baytrail: Serialize all register access

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Date:	Fri, 30 Oct 2015 12:48:38 -0200
From:	Lucas De Marchi <lucas.de.marchi@...il.com>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Mathias Nyman <mathias.nyman@...ux.intel.com>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Greg KH <gregkh@...uxfoundation.org>
Subject: Re: [PATCH 2/2] pinctrl: baytrail: Serialize all register access

Hi Mika and Linus,

CC'ing Greg.

On Tue, Aug 4, 2015 at 9:03 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> wrote:
> There is a hardware issue in Intel Baytrail where concurrent GPIO register
> access might result reads of 0xffffffff and writes might get dropped
> completely.
>
> Prevent this from happening by taking the serializing lock in all places
> where it is possible that more than one thread might be accessing the
> hardware concurrently.
>
> Signed-off-by: Mika Westerberg <mika.westerberg@...ux.intel.com>
> ---

Now that this is on 4.2, can we get it on stable branches?  I was
hitting this bug for some time on MinnowBoard Max and this week I had
some time to take a look on how to fix it. Good timing, it had already
been fixed. Applying this patch the issue is gone on top of 4.1.12.

I'm using these patches from Linus Torvalds' tree:
39ce815 pinctrl: baytrail: Serialize all register access
78e1c89 pinctrl: baytrail: Use raw_spinlock for locking


The ones to Cherryview could be sent too but I couldn't test them.

Leaving the patch below for reference.

thanks
Lucas De Marchi

>  drivers/pinctrl/intel/pinctrl-baytrail.c | 21 ++++++++++++++++-----
>  1 file changed, 16 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pinctrl/intel/pinctrl-baytrail.c b/drivers/pinctrl/intel/pinctrl-baytrail.c
> index 4b82381c9a57..f80a1bee6981 100644
> --- a/drivers/pinctrl/intel/pinctrl-baytrail.c
> +++ b/drivers/pinctrl/intel/pinctrl-baytrail.c
> @@ -196,6 +196,9 @@ static int byt_gpio_request(struct gpio_chip *chip, unsigned offset)
>         struct byt_gpio *vg = to_byt_gpio(chip);
>         void __iomem *reg = byt_gpio_reg(chip, offset, BYT_CONF0_REG);
>         u32 value, gpio_mux;
> +       unsigned long flags;
> +
> +       spin_lock_irqsave(&vg->lock, flags);
>
>         /*
>          * In most cases, func pin mux 000 means GPIO function.
> @@ -209,18 +212,16 @@ static int byt_gpio_request(struct gpio_chip *chip, unsigned offset)
>         value = readl(reg) & BYT_PIN_MUX;
>         gpio_mux = byt_get_gpio_mux(vg, offset);
>         if (WARN_ON(gpio_mux != value)) {
> -               unsigned long flags;
> -
> -               spin_lock_irqsave(&vg->lock, flags);
>                 value = readl(reg) & ~BYT_PIN_MUX;
>                 value |= gpio_mux;
>                 writel(value, reg);
> -               spin_unlock_irqrestore(&vg->lock, flags);
>
>                 dev_warn(&vg->pdev->dev,
>                          "pin %u forcibly re-configured as GPIO\n", offset);
>         }
>
> +       spin_unlock_irqrestore(&vg->lock, flags);
> +
>         pm_runtime_get(&vg->pdev->dev);
>
>         return 0;
> @@ -272,7 +273,15 @@ static int byt_irq_type(struct irq_data *d, unsigned type)
>  static int byt_gpio_get(struct gpio_chip *chip, unsigned offset)
>  {
>         void __iomem *reg = byt_gpio_reg(chip, offset, BYT_VAL_REG);
> -       return readl(reg) & BYT_LEVEL;
> +       struct byt_gpio *vg = to_byt_gpio(chip);
> +       unsigned long flags;
> +       u32 val;
> +
> +       spin_lock_irqsave(&vg->lock, flags);
> +       val = readl(reg);
> +       spin_unlock_irqrestore(&vg->lock, flags);
> +
> +       return val & BYT_LEVEL;
>  }
>
>  static void byt_gpio_set(struct gpio_chip *chip, unsigned offset, int value)
> @@ -445,8 +454,10 @@ static void byt_irq_ack(struct irq_data *d)
>         unsigned offset = irqd_to_hwirq(d);
>         void __iomem *reg;
>
> +       spin_lock(&vg->lock);
>         reg = byt_gpio_reg(&vg->chip, offset, BYT_INT_STAT_REG);
>         writel(BIT(offset % 32), reg);
> +       spin_unlock(&vg->lock);
>  }
>
>  static void byt_irq_unmask(struct irq_data *d)
> --
> 2.4.6
>
> --
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-- 
Lucas De Marchi
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