linux-kernel - Re: [PATCH v3] platform/chrome: cros_ec: Send host event for prepare/complete

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Date:   Mon, 22 Aug 2022 10:21:47 -0600
From:   Tim Van Patten <timvp@...gle.com>
To:     Tzung-Bi Shih <tzungbi@...nel.org>
Cc:     rrangel@...omium.org, robbarnes@...gle.com,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        chrome-platform@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3] platform/chrome: cros_ec: Send host event for prepare/complete

On Wed, Aug 17, 2022 at 10:08 PM Tzung-Bi Shih <tzungbi@...nel.org> wrote:
>
> On Tue, Aug 02, 2022 at 11:40:08AM -0600, Tim Van Patten wrote:
> > Update cros_ec_lpc_pm_ops to call cros_ec_lpc_prepare() during PM
> > .prepare() and cros_ec_lpc_complete() during .complete(). This allows the
> > EC to log entry/exit of AP's suspend/resume more accurately.
>
> As what I commented on [1], the term "host event" in the commit title is
> confusing.  Also, as this is a cros_ec_lpc specific patch, please change
> the prefix.

I've updated the prefix to "cros_ec_lpc" and the title/description to
indicate that this CL moves when the host event is sent to
.prepare()/.complete().

> [1]: https://patchwork.kernel.org/project/chrome-platform/patch/20220706205136.v2.1.Ic7a7c81f880ab31533652e0928aa6e687bb268b5@changeid/#24934911
>
> > -static int cros_ec_lpc_resume(struct device *dev)
> > +static void cros_ec_lpc_complete(struct device *dev)
> >  {
> >       struct cros_ec_device *ec_dev = dev_get_drvdata(dev);
> > +     int ret;
> > +
> > +     ret = cros_ec_resume(ec_dev);
> >
> > -     return cros_ec_resume(ec_dev);
> > +     dev_info(dev, "EC resume completed: ret = %d\n", ret);
>
> cros_ec_resume() always returns 0.

Yes, it always returns 0 today, but that may not be the case forever.
 While "ret" is not returned by cros_ec_resume() today, it's possible
for it to be non-zero and someone may update cros_ec_resume() to
return that status.

https://github.com/torvalds/linux/blob/1c23f9e627a7b412978b4e852793c5e3c3efc555/drivers/platform/chrome/cros_ec.c#L378

Additionally, everyone passes along the return code of cros_ec_resume():

    drivers/platform/chrome/cros_ec_i2c.c
    331:    return cros_ec_resume(ec_dev);

    drivers/platform/chrome/cros_ec_rpmsg.c
    285:    return cros_ec_resume(ec_dev);

    drivers/platform/chrome/cros_ec_ishtp.c
    766:    return cros_ec_resume(client_data->ec_dev);

    drivers/platform/chrome/cros_ec_spi.c
    808:    return cros_ec_resume(ec_dev);

    drivers/platform/chrome/cros_ec_uart.c
    390:    return cros_ec_resume(ec_dev);

    drivers/platform/chrome/cros_ec_lpc.c
    530:    return cros_ec_resume(ec_dev);

I'm going to leave this as-is, since it's good practice to check
return values (and log bad status) and so we don't need to update this
code in case cros_ec_resume() does return a non-zero value in the
future.

-- 

Tim Van Patten | ChromeOS | timvp@...gle.com | (720) 432-0997