linux-kernel - Re: [RFT PATCH v2 06/10] drivers: qcom: rpmh-rsc: Comment tcs_is

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Message-ID: <7a6edff1-3916-e802-0441-25b31989619f@codeaurora.org>
Date:   Wed, 1 Apr 2020 17:08:36 +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:     mka@...omium.org, Rajendra Nayak <rnayak@...eaurora.org>,
        evgreen@...omium.org, Lina Iyer <ilina@...eaurora.org>,
        swboyd@...omium.org, linux-arm-msm@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [RFT PATCH v2 06/10] drivers: qcom: rpmh-rsc: Comment
 tcs_is_free() + warn if state mismatch

Hi,

On 3/12/2020 4:43 AM, Douglas Anderson wrote:
> tcs_is_free() had two checks in it: does the software think that the
> TCS is free and does the hardware think that the TCS is free.  Let's
> comment this and also add a warning in the case that software and
> hardware disagree, at least for ACTIVE_ONLY TCS.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
> ---
>
> Changes in v2:
> - Comment tcs_is_free() new for v2; replaces old patch 6.
>
>   drivers/soc/qcom/rpmh-rsc.c | 23 +++++++++++++++++++++--
>   1 file changed, 21 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/soc/qcom/rpmh-rsc.c b/drivers/soc/qcom/rpmh-rsc.c
> index 9d2669cbd994..93f5d1fb71ca 100644
> --- a/drivers/soc/qcom/rpmh-rsc.c
> +++ b/drivers/soc/qcom/rpmh-rsc.c
> @@ -181,8 +181,27 @@ static void write_tcs_reg_sync(struct rsc_drv *drv, int reg, int tcs_id,
>    */
>   static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
>   {
> -	return !test_bit(tcs_id, drv->tcs_in_use) &&
> -	       read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id);
> +	/* If software thinks it's in use then it's definitely in use */
> +	if (test_bit(tcs_id, drv->tcs_in_use))
> +		return false;
> +
> +	/* If hardware agrees it's free then it's definitely free */
> +	if (read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id) != 0)
> +		return true;
> +
> +	/*
> +	 * If we're here then software and hardware disagree about whether
> +	 * the TCS is free.  Software thinks it is free and hardware thinks
> +	 * it is not.
> +	 *
> +	 * Maybe this should be a warning in all cases, but it's almost
> +	 * certainly a warning for the ACTIVE_TCS where nobody else should
> +	 * be doing anything else behind our backs.  For now we'll just
> +	 * warn there and then still return that we're in use.
> +	 */
> +	WARN(drv->tcs[tcs_id].type == ACTIVE_TCS,
> +	     "Driver thought TCS was free but HW reported busy\n");
This warning can come for borrowed WAKE_TCS as well.
> +	return false;
>   }

We have a patch on downstream variant to optimize this by only checking 
tcs_in_use flag (SW check) and HW check is removed.

  static bool tcs_is_free(struct rsc_drv *drv, int tcs_id)
  {
-       return !test_bit(tcs_id, drv->tcs_in_use) &&
-              read_tcs_reg(drv, RSC_DRV_STATUS, tcs_id, 0);
+       return !test_bit(tcs_id, drv->tcs_in_use);
  }

With this we are good and don't require to put above warning as well.

if you want me to upload, i can post it and then you can drop this 
change from your series.

Or if you want to modify it as above and keep in this series i am ok.

Thanks,
Maulik

>   
>   /**

-- 
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