linux-kernel - Re: [PATCH V5 2/2] mailbox: arm

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Date:   Fri, 20 Nov 2020 13:06:52 -0600
From:   Jassi Brar <jassisinghbrar@...il.com>
To:     Viresh Kumar <viresh.kumar@...aro.org>
Cc:     Rob Herring <robh@...nel.org>,
        Tushar Khandelwal <Tushar.Khandelwal@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        Sudeep Holla <Sudeep.Holla@....com>,
        Morten Borup Petersen <morten_bp@...e.dk>,
        Usama Arif <usama.arif@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V5 2/2] mailbox: arm_mhuv2: Add driver

On Tue, Nov 17, 2020 at 4:02 AM Viresh Kumar <viresh.kumar@...aro.org> wrote:

> +
> +/**
> + * struct mhuv2 - MHUv2 mailbox controller data
> + *
> + * @mbox:      Mailbox controller belonging to the MHU frame.
> + * @send/recv: Base address of the register mapping region.
> + * @frame:     Frame type: RECEIVER_FRAME or SENDER_FRAME.
> + * @irq:       Interrupt.
> + * @windows:   Channel windows implemented by the platform.
> + * @minor:     Minor version of the controller.
> + * @length:    Length of the protocols array in bytes.
> + * @protocols: Raw protocol information, derived from device tree.
> + * @doorbell_pending_lock: spinlock required for correct operation of Tx
> + *             interrupt for doorbells.
> + */
> +struct mhuv2 {
> +       struct mbox_controller mbox;
> +       union {
> +               struct mhu2_send_frame_reg __iomem *send;
> +               struct mhu2_recv_frame_reg __iomem *recv;
> +       };
> +       enum mhuv2_frame frame;
> +       unsigned int irq;
> +       unsigned int windows;
> +       unsigned int minor;
> +       unsigned int length;
> +       u32 *protocols;
> +
> +       spinlock_t doorbell_pending_lock;
>
Can you please explain the need of this lock? Some usecase?
It should be unnecessary if the controller natively supports doorbell mode.

thanks.