Hi,
On 6/2/20 5:23 PM, Andy Shevchenko wrote:
On Tue, Jun 02, 2020 at 02:21:30PM +0200, Hans de Goede wrote:
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.
No Fixes tag?
It is sort of hard to pin the introduction of this down to a single
commit. If I were to guess, I guess the commit introducing the driver?
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
...
+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
Since we change this, perhaps
'IRQ. On baytrail' -> 'IRQ. On Baytrail' (one space and capital 'B').
Sure, not sure if that is worth respinning the patch for though,
either way let me know.
+ * 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_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;
}
Wouldn't be simple below fix the issue?
@@ -1171,14 +1171,10 @@ 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);
-
- if (ret)
- return ret;
-
+ /* Set value first to avoid a glitch */
byt_gpio_set(chip, offset, value);
- return 0;
+ return pinctrl_gpio_direction_output(chip->base + offset);
}
No that will not help the pin is already high, but any reads
of the register will return the BYT_LEVEL bit as being low, so
the read-write-modify done when setting the direction reads BYT_LEVEL
as 0 and writes it back as such.
So your proposal would actually make the problem much worse (and more
obvious) if we do the byt_gpio_set() first then for pins which have
there input-buffer initially disabled, the value passed to
byt_gpio_direction_output will be completely ignored and they will
always end up as being driven low.
Regards,
Hans
