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

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Date:   Mon, 24 Aug 2020 13:35:57 +0200
From:   Ulf Hansson <ulf.hansson@...aro.org>
To:     Maulik Shah <mkshah@...eaurora.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Lina Iyer <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 1/2] Revert "drivers: qcom: rpmh-rsc: Use rcuidle
 tracepoints for rpmh"

On Wed, 19 Aug 2020 at 12:08, Maulik Shah <mkshah@...eaurora.org> wrote:
>
> This change was done based on an test results of unmerged series of
> adding RSC power domain and using .power_off callback of genpd to
> invoke rpmh_flush().
>
>      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.
>
> 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>
> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>

Along with Stephen's comments, feel free to add:

Reviewed-by: Ulf Hansson <ulf.hansson@...aro.org>

Also note, when using the PSCI OSI mode, I am proposing to use "genpd
on/off notifiers" [1]. This may lead to similar RCU issues, but let's
come back to adress that later on, when/if needed.

Kind regards
Uffe

[1]
https://www.spinics.net/lists/kernel/msg3629443.html


> ---
>  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
>