linux-kernel - RE: [PATCH v3 1/2] gpio: mlxbf2: Introduce IRQ support

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Date:   Fri, 8 Oct 2021 14:47:21 +0000
From:   Asmaa Mnebhi <asmaa@...dia.com>
To:     Andrew Lunn <andrew@...n.ch>
CC:     Linus Walleij <linus.walleij@...aro.org>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        "open list:GPIO SUBSYSTEM" <linux-gpio@...r.kernel.org>,
        netdev <netdev@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Jakub Kicinski <kuba@...nel.org>,
        Bartosz Golaszewski <bgolaszewski@...libre.com>,
        "David S. Miller" <davem@...emloft.net>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        David Thompson <davthompson@...dia.com>
Subject: RE: [PATCH v3 1/2] gpio: mlxbf2: Introduce IRQ support

> In KSZ9031, Register MII_KSZPHY_INTCS=0x1B reports all interrupt 
> events and clear on read. So if there are 4 different interrupts, once it is read once, all 4 clear at once.
> The micrel.c driver has defined ack_interrupt to read the above reg 
> and is called every time the interrupt handler phy_interrupt is called. So in this case, we should be good.
> The code flow in our case would look like this:
> - 2 interrupt sources (for example, link down followed by link up) set 
> in MII_KSZPHY_INTCS
> - interrupt handler (phy_interrupt) reads MII_KSZPHY_INT which 
> automatically clears both interrupts
> - another internal source triggers and sets the register.
> - The second edge will be caught accordingly by the GPIO.

> I still think there is a small race window. You product manager needs to decide if that is acceptable, or if you should poll the PHY.

I talked to both our managers and the HW team and they said it is ok to use the interrupt for our product.

> Anyway, it is clear the hardware only does level interrupts, so the GPIO driver should only accept level interrupts. -EINVAL otherwise.

There is an on going conversation with HW folks to address this for future BlueField generations.

Thank you.
Asmaa