linux-kernel - Re: [PATCH] pinctrl: cherryview: Serialize all register access

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Message-ID: <CACRpkdYj_gBQpRqPP4S3c-cPhzRGnGUahh+1L8G5qUxwG=cx0g@mail.gmail.com>
Date:	Thu, 13 Aug 2015 13:24:13 +0200
From:	Linus Walleij <linus.walleij@...aro.org>
To:	Mika Westerberg <mika.westerberg@...ux.intel.com>
Cc:	"linux-gpio@...r.kernel.org" <linux-gpio@...r.kernel.org>,
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] pinctrl: cherryview: Serialize all register access

On Mon, Aug 3, 2015 at 11:46 AM, Mika Westerberg
<mika.westerberg@...ux.intel.com> 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@...ux.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
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