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Date:   Wed, 15 Apr 2020 11:25:36 -0700
From:   Matthias Kaehlcke <mka@chromium.org>
To:     John Stultz <john.stultz@linaro.org>
Cc:     lkml <linux-kernel@vger.kernel.org>, Todd Kjos <tkjos@google.com>,
        Saravana Kannan <saravanak@google.com>,
        Andy Gross <agross@kernel.org>,
        Bjorn Andersson <bjorn.andersson@linaro.org>,
        Rajendra Nayak <rnayak@codeaurora.org>,
        linux-arm-msm@vger.kernel.org,
        Steven Rostedt <rostedt@goodmis.org>,
        Stephen Boyd <swboyd@chromium.org>,
        Douglas Anderson <dianders@chromium.org>
Subject: Re: [PATCH v3 2/3] soc: qcom: rpmh: Allow RPMH driver to be loaded
 as a module
Message-ID: <20200415182536.GX199755@google.com>
References: <20200326224459.105170-1-john.stultz@linaro.org>
 <20200326224459.105170-3-john.stultz@linaro.org>
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Hi John,

with commit efde2659b0fe ("drivers: qcom: rpmh-rsc: Use rcuidle
tracepoints for rpmh") the rpmh-rsc driver fails to build as a
module:

drivers/soc/qcom/rpmh-rsc.c:281:3: error: implicit declaration of function 'trace_rpmh_send_msg_rcuidle' [-Werror,-Wimplicit-function-decr]
                trace_rpmh_send_msg_rcuidle(drv, tcs_id, j, msgid, cmd);


The problem is that the _rcuidle() functions are not generated for modules:

#ifndef MODULE
#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args) \
	static inline void trace_##name##_rcuidle(proto)		\
	{								\
		if (static_key_false(&__tracepoint_##name.key))		\
			__DO_TRACE(&__tracepoint_##name,		\
				TP_PROTO(data_proto),			\
				TP_ARGS(data_args),			\
				TP_CONDITION(cond), 1);			\
	}
#else
#define __DECLARE_TRACE_RCU(name, proto, args, cond, data_proto, data_args)
#endif

Not sure what the best solution would be in this case. Having the macro
define a dummy function for modules would fix the build error, however it
would be confusing that the event is traced when the driver is built-in,
but not when it is built as a module.

I imagine the goal behind making this driver a module is to have a single
kernel image for multiple SoC platforms, without too much platform
specific code in the kernel image itself.

I guess the question is whether there any options for keeping the driver
modular and having consistent tracing behavior, short of removing the
tracepoint.

On Thu, Mar 26, 2020 at 10:44:58PM +0000, John Stultz wrote:
> This patch allow the rpmh driver to be loaded as a permenent
> module. Meaning it can be loaded from a module, but then cannot
> be unloaded.
> 
> Ideally, it would include a remove hook and related logic, but
> the rpmh driver is fairly core to the system, so once its loaded
> with almost anythign else to get the system to go, the dependencies
> are not likely to ever also be removed.
> 
> So making it a permenent module at least improves things slightly
> over requiring it to be a built in driver.
> 
> Feedback would be appreciated!
> 
> Cc: Todd Kjos <tkjos@google.com>
> Cc: Saravana Kannan <saravanak@google.com>
> Cc: Andy Gross <agross@kernel.org>
> Cc: Bjorn Andersson <bjorn.andersson@linaro.org>
> Cc: Rajendra Nayak <rnayak@codeaurora.org>
> Cc: linux-arm-msm@vger.kernel.org
> Signed-off-by: John Stultz <john.stultz@linaro.org>
> ---
>  drivers/soc/qcom/Kconfig    | 2 +-
>  drivers/soc/qcom/rpmh-rsc.c | 6 ++++++
>  2 files changed, 7 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/Kconfig b/drivers/soc/qcom/Kconfig
> index af774555b9d2..ac91eaf810f7 100644
> --- a/drivers/soc/qcom/Kconfig
> +++ b/drivers/soc/qcom/Kconfig
> @@ -104,7 +104,7 @@ config QCOM_RMTFS_MEM
>  	  Say y here if you intend to boot the modem remoteproc.
>  
>  config QCOM_RPMH
> -	bool "Qualcomm RPM-Hardened (RPMH) Communication"
> +	tristate "Qualcomm RPM-Hardened (RPMH) Communication"
>  	depends on ARCH_QCOM && ARM64 || COMPILE_TEST
>  	help
>  	  Support for communication with the hardened-RPM blocks in
> diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> index e278fc11fe5c..30585d98fdf1 100644
> --- a/drivers/soc/qcom/rpmh-rsc.c
> +++ b/drivers/soc/qcom/rpmh-rsc.c
> @@ -11,6 +11,7 @@
>  #include <linux/io.h>
>  #include <linux/kernel.h>
>  #include <linux/list.h>
> +#include <linux/module.h>
>  #include <linux/of.h>
>  #include <linux/of_irq.h>
>  #include <linux/of_platform.h>
> @@ -679,6 +680,8 @@ static const struct of_device_id rpmh_drv_match[] = {
>  	{ .compatible = "qcom,rpmh-rsc", },
>  	{ }
>  };
> +MODULE_DEVICE_TABLE(of, rpmh_drv_match);
> +
>  
>  static struct platform_driver rpmh_driver = {
>  	.probe = rpmh_rsc_probe,
> @@ -693,3 +696,6 @@ static int __init rpmh_driver_init(void)
>  	return platform_driver_register(&rpmh_driver);
>  }
>  arch_initcall(rpmh_driver_init);
> +
> +MODULE_DESCRIPTION("Qualcomm Technologies, Inc. RPMh Driver");
> +MODULE_LICENSE("GPL v2");
> -- 
> 2.17.1
>