The pins on the Bay Trail SoC have separate input-buffer and output-buffer enable bits and a read of the level bit of the value register will always return the value from the input-buffer.

The BIOS of a device may configure a pin in output-only mode, only enabling the output buffer, and write 1 to the level bit to drive the pin high. This 1 written to the level bit will be stored inside the data-latch of the output buffer.

But a subsequent read of the value register will return 0 for the level bit because the input-buffer is disabled. This causes a read-modify-write as done by byt_gpio_set_direction() to write 0 to the level bit, driving the pin low!

Before this commit byt_gpio_direction_output() relied on pinctrl_gpio_direction_output() to set the direction, followed by a call to byt_gpio_set() to apply the selected value. This causes the pin to go low between the pinctrl_gpio_direction_output() and byt_gpio_set() calls.

Change byt_gpio_direction_output() to directly make the register modifications itself instead. Replacing the 2 subsequent writes to the value register with a single write.

Note that the pinctrl code does not keep track internally of the direction, so not going through pinctrl_gpio_direction_output() is not an issue.

This issue was noticed on a Trekstor SurfTab Twin 10.1. When the panel is already on at boot (no external monitor connected), then the i915 driver does a gpiod_get(..., GPIOD_OUT_HIGH) for the panel-enable GPIO. The temporarily going low of that GPIO was causing the panel to reset itself after which it would not show an image until it was turned off and back on again (until a full modeset was done on it). This commit fixes this.

Cc: stable@vger.kernel.org Signed-off-by: Hans de Goede hdegoede@redhat.com --- Note the factoring out of the direct IRQ mode warning is deliberately not split into a separate patch to make backporting this easier. --- drivers/pinctrl/intel/pinctrl-baytrail.c | 46 +++++++++++++++++------- 1 file changed, 33 insertions(+), 13 deletions(-)

diff --git a/drivers/pinctrl/intel/pinctrl-baytrail.c b/drivers/pinctrl/intel/pinctrl-baytrail.c index 9b821c9cbd16..83be13b83eb5 100644 --- a/drivers/pinctrl/intel/pinctrl-baytrail.c +++ b/drivers/pinctrl/intel/pinctrl-baytrail.c @@ -800,6 +800,21 @@ static void byt_gpio_disable_free(struct pinctrl_dev *pctl_dev, pm_runtime_put(vg->dev); }

+static void byt_gpio_direct_irq_check(struct intel_pinctrl *vg, + unsigned int offset) +{ + void __iomem *conf_reg = byt_gpio_reg(vg, offset, BYT_CONF0_REG); + + /* + * Before making any direction modifications, do a check if gpio is set + * for direct IRQ. On baytrail, setting GPIO to output does not make + * sense, so let's at least inform the caller before they shoot + * themselves in the foot. + */ + if (readl(conf_reg) & BYT_DIRECT_IRQ_EN) + dev_info_once(vg->dev, "Potential Error: Setting GPIO with direct_irq_en to output"); +} + static int byt_gpio_set_direction(struct pinctrl_dev *pctl_dev, struct pinctrl_gpio_range *range, unsigned int offset, @@ -807,7 +822,6 @@ static int byt_gpio_set_direction(struct pinctrl_dev *pctl_dev, { struct intel_pinctrl *vg = pinctrl_dev_get_drvdata(pctl_dev); void __iomem *val_reg = byt_gpio_reg(vg, offset, BYT_VAL_REG); - void __iomem *conf_reg = byt_gpio_reg(vg, offset, BYT_CONF0_REG); unsigned long flags; u32 value;

@@ -817,14 +831,8 @@ static int byt_gpio_set_direction(struct pinctrl_dev *pctl_dev, value &= ~BYT_DIR_MASK; if (input) value |= BYT_OUTPUT_EN; - else if (readl(conf_reg) & BYT_DIRECT_IRQ_EN) - /* - * Before making any direction modifications, do a check if gpio - * is set for direct IRQ. On baytrail, setting GPIO to output - * does not make sense, so let's at least inform the caller before - * they shoot themselves in the foot. - */ - dev_info_once(vg->dev, "Potential Error: Setting GPIO with direct_irq_en to output"); + else + byt_gpio_direct_irq_check(vg, offset);

writel(value, val_reg);

@@ -1171,13 +1179,25 @@ static int byt_gpio_direction_input(struct gpio_chip *chip, unsigned int offset) static int byt_gpio_direction_output(struct gpio_chip *chip, unsigned int offset, int value) { - int ret = pinctrl_gpio_direction_output(chip->base + offset); + struct intel_pinctrl *vg = gpiochip_get_data(chip); + void __iomem *val_reg = byt_gpio_reg(vg, offset, BYT_VAL_REG); + unsigned long flags; + u32 reg;

- if (ret) - return ret; + raw_spin_lock_irqsave(&byt_lock, flags);

- byt_gpio_set(chip, offset, value); + byt_gpio_direct_irq_check(vg, offset);

+ reg = readl(val_reg); + reg &= ~BYT_DIR_MASK; + if (value) + reg |= BYT_LEVEL; + else + reg &= ~BYT_LEVEL; + + writel(reg, val_reg); + + raw_spin_unlock_irqrestore(&byt_lock, flags); return 0; }