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

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Message-ID: <159546542444.3847286.3076597427214316886@swboyd.mtv.corp.google.com>
Date:   Wed, 22 Jul 2020 17:50:24 -0700
From:   Stephen Boyd <swboyd@...omium.org>
To:     Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Douglas Anderson <dianders@...omium.org>
Cc:     linux-arm-msm@...r.kernel.org,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Akash Asthana <akashast@...eaurora.org>,
        Sai Prakash Ranjan <saiprakash.ranjan@...eaurora.org>,
        Wolfram Sang <wsa@...-dreams.de>, msavaliy@...eaurora.org,
        Douglas Anderson <dianders@...omium.org>,
        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

Quoting Douglas Anderson (2020-07-22 15:01:20)
> 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: Stephen Boyd <swboyd@...omium.org>