linux-kernel - Re: [PATCH v2 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle tracepoints for rpmh"

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Message-ID: <20200827015336.GG3715@yoga>
Date:   Wed, 26 Aug 2020 20:53:36 -0500
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     andy.gross@...aro.org, linux-kernel@...r.kernel.org,
        linux-arm-msm@...r.kernel.org, ulf.hansson@...aro.org,
        swboyd@...omium.org, dianders@...omium.org, rnayak@...eaurora.org,
        ilina@...eaurora.org, lsrao@...eaurora.org,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        John Stultz <john.stultz@...aro.org>,
        Stephen Rothwell <sfr@...b.auug.org.au>
Subject: Re: [PATCH v2 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle
 tracepoints for rpmh"

On Tue 25 Aug 06:21 CDT 2020, Maulik Shah wrote:

> Commit efde2659b0fe ("drivers: qcom: rpmh-rsc: Use rcuidle tracepoints
> for rpmh") was written to fix a bug seen in an unmerged series that
> implemented a struct generic_pm_domain::power_off() callback calling
> rpmh_flush(). See stack trace below.
> 
>      Call trace:
>       dump_backtrace+0x0/0x174
>       show_stack+0x20/0x2c
>       dump_stack+0xc8/0x124
>       lockdep_rcu_suspicious+0xe4/0x104
>       __tcs_buffer_write+0x230/0x2d0
>       rpmh_rsc_write_ctrl_data+0x210/0x270
>       rpmh_flush+0x84/0x24c
>       rpmh_domain_power_off+0x78/0x98
>       _genpd_power_off+0x40/0xc0
>       genpd_power_off+0x168/0x208
> 
> Later the final merged solution is to use CPU PM notification to invoke
> rpmh_flush() and power_off() callback of genpd is not implemented in the
> driver.
> 
> CPU PM notifiers are run with RCU enabled/watching (see cpu_pm_notify()
> and how it calls rcu_irq_enter_irqson() before calling the notifiers).
> 
> Remove this change since RCU will not be idle during CPU PM notifications
> hence not required to use _rcuidle tracepoint. Using _rcuidle tracepoint
> prevented rpmh driver to be loadable module as these are not exported
> symbols.
> 
> This reverts commit efde2659b0fe835732047357b2902cca14f054d9.
> 
> Cc: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> Cc: John Stultz <john.stultz@...aro.org>
> Cc: Stephen Rothwell <sfr@...b.auug.org.au>
> Reviewed-by: Stephen Boyd <swboyd@...omium.org>
> Reviewed-by: Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>
> Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@...aro.org>

Regards,
Bjorn

> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
> ---
>  drivers/soc/qcom/rpmh-rsc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> index ae66757..fabe390d 100644
> --- a/drivers/soc/qcom/rpmh-rsc.c
> +++ b/drivers/soc/qcom/rpmh-rsc.c
> @@ -495,7 +495,7 @@ static void __tcs_buffer_write(struct rsc_drv *drv, int tcs_id, int cmd_id,
>  		write_tcs_cmd(drv, RSC_DRV_CMD_MSGID, tcs_id, j, msgid);
>  		write_tcs_cmd(drv, RSC_DRV_CMD_ADDR, tcs_id, j, cmd->addr);
>  		write_tcs_cmd(drv, RSC_DRV_CMD_DATA, tcs_id, j, cmd->data);
> -		trace_rpmh_send_msg_rcuidle(drv, tcs_id, j, msgid, cmd);
> +		trace_rpmh_send_msg(drv, tcs_id, j, msgid, cmd);
>  	}
>  
>  	write_tcs_reg(drv, RSC_DRV_CMD_WAIT_FOR_CMPL, tcs_id, cmd_complete);
> -- 
> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member
> of Code Aurora Forum, hosted by The Linux Foundation
>