linux-kernel - Re: [PATCH 5/9] soc: apple: Add RTKit IPC library

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Message-ID: <CAK8P3a2VgrWHerXTX4_wS8UU7fpN9-JZ5xESaWrr-WGYqGty=g@mail.gmail.com>
Date:   Tue, 22 Mar 2022 14:13:53 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     Sven Peter <sven@...npeter.dev>
Cc:     Hector Martin <marcan@...can.st>,
        Alyssa Rosenzweig <alyssa@...enzweig.io>,
        Rob Herring <robh+dt@...nel.org>,
        Arnd Bergmann <arnd@...db.de>, Keith Busch <kbusch@...nel.org>,
        Jens Axboe <axboe@...com>, Christoph Hellwig <hch@....de>,
        Sagi Grimberg <sagi@...mberg.me>,
        Marc Zyngier <maz@...nel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-nvme@...ts.infradead.org
Subject: Re: [PATCH 5/9] soc: apple: Add RTKit IPC library

On Mon, Mar 21, 2022 at 5:50 PM Sven Peter <sven@...npeter.dev> wrote:
>
> Apple SoCs such as the M1 come with multiple embedded co-processors
> running proprietary firmware. Communication with those is established
> over a simple mailbox using the RTKit IPC protocol.
>
> Signed-off-by: Sven Peter <sven@...npeter.dev>

> +
> +#define rtk_err(format, arg...) dev_err(rtk->dev, "RTKit: " format, ##arg)
> +#define rtk_warn(format, arg...) dev_warn(rtk->dev, "RTKit: " format, ##arg)
> +#define rtk_info(format, arg...) dev_info(rtk->dev, "RTKit: " format, ##arg)
> +#define rtk_dbg(format, arg...) dev_dbg(rtk->dev, "RTKit: " format, ##arg)

I generally don't like the custom printing macros, please just open-code
the prints where they are used, that makes it easier for other kernel
developers to see exactly what is being printed.

> +enum { APPLE_RTKIT_WORK_MSG,
> +       APPLE_RTKIT_WORK_REINIT,
> +};
> +
> +enum { APPLE_RTKIT_PWR_STATE_OFF = 0x00,
> +       APPLE_RTKIT_PWR_STATE_SLEEP = 0x01,
> +       APPLE_RTKIT_PWR_STATE_GATED = 0x02,
> +       APPLE_RTKIT_PWR_STATE_QUIESCED = 0x10,
> +       APPLE_RTKIT_PWR_STATE_ON = 0x20,
> +};

This is an odd indentation style, I would insert a newline after the 'enum {'

> +static int apple_rtkit_worker(void *data)
> +{
> +       struct apple_rtkit *rtk = data;
> +       struct apple_rtkit_work work;
> +
> +       while (!kthread_should_stop()) {
> +               wait_event_interruptible(rtk->wq,
> +                                        kfifo_len(&rtk->work_fifo) > 0 ||
> +                                                kthread_should_stop());
> +
> +               if (kthread_should_stop())
> +                       break;
> +
> +               while (kfifo_out_spinlocked(&rtk->work_fifo, &work, 1,
> +                                           &rtk->work_lock) == 1) {
> +                       switch (work.type) {
> +                       case APPLE_RTKIT_WORK_MSG:
> +                               apple_rtkit_rx(rtk, &work.msg);
> +                               break;
> +                       case APPLE_RTKIT_WORK_REINIT:
> +                               apple_rtkit_do_reinit(rtk);
> +                               break;
> +                       }
> +               }

It looks like you add quite a bit of complexity by using a custom
worker thread implementation. Can you explain what this is
needed for? Isn't this roughly the same thing that one would
get more easily with create_singlethread_workqueue()?

> +#if IS_ENABLED(CONFIG_APPLE_RTKIT)

Instead of allowing the interface to be used without CONFIG_APPLE_RTKIT,
I think it is sufficient to allow the driver itself to be built with
CONFIG_COMPILE_TEST (as you already do), and then have
drivers using it marked as 'depends on APPLE_RTKIT'
unconditionally.

> +/*
> + * Initializes the internal state required to handle RTKit. This
> + * should usually be called within _probe.
> + *
> + * @dev: Pointer to the device node this coprocessor is assocated with
> + * @cookie: opaque cookie passed to all functions defined in rtkit_ops
> + * @mbox_name: mailbox name used to communicate with the co-processor
> + * @mbox_idx: mailbox index to be used if mbox_name is NULL
> + * @ops: pointer to rtkit_ops to be used for this co-processor
> + */
> +struct apple_rtkit *apple_rtkit_init(struct device *dev, void *cookie,
> +                                    const char *mbox_name, int mbox_idx,
> +                                    const struct apple_rtkit_ops *ops);
> +
> +/*
> + * Dev-res managed version of apple_rtkit_init.
> + */
> +struct apple_rtkit *devm_apple_rtkit_init(struct device *dev, void *cookie,
> +                                         const char *mbox_name, int mbox_idx,
> +                                         const struct apple_rtkit_ops *ops);

Do we need to export both of these?

         Arnd