linux-kernel - Re: [PATCH] soc: qcom: rpmh-rsc: Don't use ktime for timeout in write_tcs_reg

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Message-ID: <2eb7c28e-d7af-8bc8-c308-46f4df5c995c@codeaurora.org>
Date:   Wed, 24 Jun 2020 10:11:52 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     Stephen Boyd <swboyd@...omium.org>, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: qcom: rpmh-rsc: Don't use ktime for timeout in
 write_tcs_reg_sync()

Reviewed-by: Maulik Shah <mkshah@...eaurora.org>

Thanks,
Maulik

On 5/28/2020 8:18 PM, Douglas Anderson wrote:
> The write_tcs_reg_sync() may be called after timekeeping is suspended
> so it's not OK to use ktime.  The readl_poll_timeout_atomic() macro
> implicitly uses ktime.  This was causing a warning at suspend time.
>
> Change to just loop 1000000 times with a delay of 1 us between loops.
> This may give a timeout of more than 1 second but never less and is
> safe even if timekeeping is suspended.
>
> NOTE: I don't have any actual evidence that we need to loop here.
> It's possibly that all we really need to do is just read the value
> back to ensure that the pipes are cleaned and the looping/comparing is
> totally not needed.  I never saw the loop being needed in my tests.
> However, the loop shouldn't hurt.
>
> Fixes: 91160150aba0 ("soc: qcom: rpmh-rsc: Timeout after 1 second in write_tcs_reg_sync()")
> Reported-by: Maulik Shah <mkshah@...eaurora.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
>   drivers/soc/qcom/rpmh-rsc.c | 18 +++++++++++++-----
>   1 file changed, 13 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> index 076fd27f3081..906778e2c1fa 100644
> --- a/drivers/soc/qcom/rpmh-rsc.c
> +++ b/drivers/soc/qcom/rpmh-rsc.c
> @@ -175,13 +175,21 @@ static void write_tcs_reg(const struct rsc_drv *drv, int reg, int tcs_id,
>   static void write_tcs_reg_sync(const struct rsc_drv *drv, int reg, int tcs_id,
>   			       u32 data)
>   {
> -	u32 new_data;
> +	int i;
>   
>   	writel(data, tcs_reg_addr(drv, reg, tcs_id));
> -	if (readl_poll_timeout_atomic(tcs_reg_addr(drv, reg, tcs_id), new_data,
> -				      new_data == data, 1, USEC_PER_SEC))
> -		pr_err("%s: error writing %#x to %d:%#x\n", drv->name,
> -		       data, tcs_id, reg);
> +
> +	/*
> +	 * Wait until we read back the same value.  Use a counter rather than
> +	 * ktime for timeout since this may be called after timekeeping stops.
> +	 */
> +	for (i = 0; i < USEC_PER_SEC; i++) {
> +		if (readl(tcs_reg_addr(drv, reg, tcs_id)) == data)
> +			return;
> +		udelay(1);
> +	}
> +	pr_err("%s: error writing %#x to %d:%#x\n", drv->name,
> +	       data, tcs_id, reg);
>   }
>   
>   /**

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