linux-kernel - Re: [PATCH] soc: qcom-geni-se: Don't use relaxed writes when writing commands

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Message-ID: <c41ccd0e-e18b-02eb-79b7-2cad604b5090@codeaurora.org>
Date:   Thu, 23 Jul 2020 14:27:20 +0530
From:   "Mukesh, Savaliya" <msavaliy@...eaurora.org>
To:     Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>
Cc:     linux-arm-msm@...r.kernel.org, swboyd@...omium.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Akash Asthana <akashast@...eaurora.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Matthias Kaehlcke <mka@...omium.org>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] soc: qcom-geni-se: Don't use relaxed writes when writing
 commands


On 7/23/2020 3:31 AM, Douglas Anderson wrote:
> Writing the command is the final step in kicking off a transfer.
> Let's use writel() to ensure that any other memory accesses are done
> before the command kicks off.  It's expected that this is mostly
> relevant if we're in DMA mode but since it doesn't appear to regress
> performance in a measurable way [1] even in PIO mode and it's easier
> to reason about then let's just always use it.
>
> NOTE: this patch came about due to code inspection.  No actual
> problems were observed that this patch fixes.
>
> [1] Tested by timing "flashrom -p ec" on a Chromebook which stresses
> GENI SPI a lot.
>
> Suggested-by: Stephen Boyd <swboyd@...omium.org>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
Reviewed-by: Mukesh Kumar Savaliya <msavaliy@...eaurora.org>
> ---
>
>   include/linux/qcom-geni-se.h | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/include/linux/qcom-geni-se.h b/include/linux/qcom-geni-se.h
> index dd464943f717..f50c73be1428 100644
> --- a/include/linux/qcom-geni-se.h
> +++ b/include/linux/qcom-geni-se.h
> @@ -262,7 +262,7 @@ static inline void geni_se_setup_m_cmd(struct geni_se *se, u32 cmd, u32 params)
>   	u32 m_cmd;
>   
>   	m_cmd = (cmd << M_OPCODE_SHFT) | (params & M_PARAMS_MSK);
> -	writel_relaxed(m_cmd, se->base + SE_GENI_M_CMD0);
> +	writel(m_cmd, se->base + SE_GENI_M_CMD0);
>   }
>   
>   /**
> @@ -282,7 +282,7 @@ static inline void geni_se_setup_s_cmd(struct geni_se *se, u32 cmd, u32 params)
>   	s_cmd &= ~(S_OPCODE_MSK | S_PARAMS_MSK);
>   	s_cmd |= (cmd << S_OPCODE_SHFT);
>   	s_cmd |= (params & S_PARAMS_MSK);
> -	writel_relaxed(s_cmd, se->base + SE_GENI_S_CMD0);
> +	writel(s_cmd, se->base + SE_GENI_S_CMD0);
>   }
>   
>   /**