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

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Date:   Wed, 22 Jul 2020 15:01:20 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     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>, 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: [PATCH] soc: qcom-geni-se: Don't use relaxed writes when writing commands

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>
---

 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);
 }
 
 /**
-- 
2.28.0.rc0.142.g3c755180ce-goog