On Mon, Aug 3, 2015 at 11:46 AM, Mika Westerberg
[off-list ref] wrote:

There is a hardware issue in Intel Braswell/Cherryview where concurrent
GPIO register access might results reads of 0xffffffff and writes might get
dropped.

Prevent this from happening by taking the serializing lock for all places
where it is possible that more than one thread might be accessing the
hardware concurrently.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>

Patch applied.

When we are on the topic of this spinlock, I noticed that you
take it in some IRQ functions:

static void chv_gpio_irq_ack(struct irq_data *d)
{
        struct gpio_chip *gc = irq_data_get_irq_chip_data(d);
        struct chv_pinctrl *pctrl = gpiochip_to_pinctrl(gc);
        int pin = chv_gpio_offset_to_pin(pctrl, irqd_to_hwirq(d));
        u32 intr_line;

        spin_lock(&pctrl->lock);
(...)

The Realtime tree have recently started to push raw spinlocks
into GPIO drivers that handle IRQs. Can you look into this
for the Intel drivers, I think maybe this needs to be a raw
spinlock to play nicely with realtime.

Cf:
http://marc.info/?l=linux-gpio&m=143749603401220&w=2

Yours,
Linus Walleij