linux-kernel - [PATCH v2 3/3] soc: qcom: geni: Optimize/comment select fifo/dma mode

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Message-Id: <20201013142448.v2.3.I646736d3969dc47de8daceb379c6ba85993de9f4@changeid>
Date:   Tue, 13 Oct 2020 14:25:30 -0700
From:   Douglas Anderson <dianders@...omium.org>
To:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Akash Asthana <akashast@...eaurora.org>
Cc:     linux-i2c@...r.kernel.org,
        Roja Rani Yarubandi <rojay@...eaurora.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
        linux-arm-msm@...r.kernel.org,
        Douglas Anderson <dianders@...omium.org>,
        Andy Gross <agross@...nel.org>, linux-kernel@...r.kernel.org
Subject: [PATCH v2 3/3] soc: qcom: geni: Optimize/comment select fifo/dma mode

The functions geni_se_select_fifo_mode() and
geni_se_select_fifo_mode() are a little funny.  They read/write a
bunch of memory mapped registers even if they don't change or aren't
relevant for the current protocol.  Let's make them a little more
sane.  We'll also add a comment explaining why we don't do some of the
operations for UART.

NOTE: there is no evidence at all that this makes any performance
difference and it fixes no bugs.  However, it seems (to me) like it
makes the functions a little easier to understand.  Decreasing the
amount of times we read/write memory mapped registers is also nice,
even if we are using "relaxed" variants.

Signed-off-by: Douglas Anderson <dianders@...omium.org>
---
Note that I didn't add Dmitry Baryshkov's Tested-by tag to the 3rd
patch since it changed subtly.  Also note that when adding comments
about why the UART is special it seems clear to me that we really
shouldn't be managing these interrupt enables in the common code.  It
seems like drivers should manage / enable the interrupts that they
care about.  That seems like a bigger change, though, and I didn't
want to muddy the waters and potentially delay the important fix from
patch #1 and #2.  Hopefully someone from Qualcomm can take on cleaning
this stuff up after these fixes land.

Changes in v2:
- Consistently use "val_old" to keep track of old value.
- Add comments about why UART is special.

 drivers/soc/qcom/qcom-geni-se.c | 50 +++++++++++++++++++++------------
 1 file changed, 32 insertions(+), 18 deletions(-)

diff --git a/drivers/soc/qcom/qcom-geni-se.c b/drivers/soc/qcom/qcom-geni-se.c
index 751a49f6534f..7649b2057b9a 100644
--- a/drivers/soc/qcom/qcom-geni-se.c
+++ b/drivers/soc/qcom/qcom-geni-se.c
@@ -266,49 +266,63 @@ EXPORT_SYMBOL(geni_se_init);
 static void geni_se_select_fifo_mode(struct geni_se *se)
 {
 	u32 proto = geni_se_read_proto(se);
-	u32 val;
+	u32 val, val_old;
 
 	geni_se_irq_clear(se);
 
-	val = readl_relaxed(se->base + SE_GENI_M_IRQ_EN);
+	/*
+	 * The RX path for the UART is asynchronous and so needs more
+	 * complex logic for enabling / disabling its interrupts.
+	 *
+	 * Specific notes:
+	 * - The done and TX-related interrupts are managed manually.
+	 * - We don't RX from the main sequencer (we use the secondary) so
+	 *   we don't need the RX-related interrupts enabled in the main
+	 *   sequencer for UART.
+	 */
 	if (proto != GENI_SE_UART) {
+		val_old = val = readl_relaxed(se->base + SE_GENI_M_IRQ_EN);
 		val |= M_CMD_DONE_EN | M_TX_FIFO_WATERMARK_EN;
 		val |= M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN;
-	}
-	writel_relaxed(val, se->base + SE_GENI_M_IRQ_EN);
+		if (val != val_old)
+			writel_relaxed(val, se->base + SE_GENI_M_IRQ_EN);
 
-	val = readl_relaxed(se->base + SE_GENI_S_IRQ_EN);
-	if (proto != GENI_SE_UART)
+		val_old = val = readl_relaxed(se->base + SE_GENI_S_IRQ_EN);
 		val |= S_CMD_DONE_EN;
-	writel_relaxed(val, se->base + SE_GENI_S_IRQ_EN);
+		if (val != val_old)
+			writel_relaxed(val, se->base + SE_GENI_S_IRQ_EN);
+	}
 
-	val = readl_relaxed(se->base + SE_GENI_DMA_MODE_EN);
+	val_old = val = readl_relaxed(se->base + SE_GENI_DMA_MODE_EN);
 	val &= ~GENI_DMA_MODE_EN;
-	writel_relaxed(val, se->base + SE_GENI_DMA_MODE_EN);
+	if (val != val_old)
+		writel_relaxed(val, se->base + SE_GENI_DMA_MODE_EN);
 }
 
 static void geni_se_select_dma_mode(struct geni_se *se)
 {
 	u32 proto = geni_se_read_proto(se);
-	u32 val;
+	u32 val, val_old;
 
 	geni_se_irq_clear(se);
 
-	val = readl_relaxed(se->base + SE_GENI_M_IRQ_EN);
 	if (proto != GENI_SE_UART) {
+		val_old = val = readl_relaxed(se->base + SE_GENI_M_IRQ_EN);
 		val &= ~(M_CMD_DONE_EN | M_TX_FIFO_WATERMARK_EN);
 		val &= ~(M_RX_FIFO_WATERMARK_EN | M_RX_FIFO_LAST_EN);
-	}
-	writel_relaxed(val, se->base + SE_GENI_M_IRQ_EN);
+		if (val != val_old)
+			writel_relaxed(val, se->base + SE_GENI_M_IRQ_EN);
 
-	val = readl_relaxed(se->base + SE_GENI_S_IRQ_EN);
-	if (proto != GENI_SE_UART)
+		val_old = val = readl_relaxed(se->base + SE_GENI_S_IRQ_EN);
 		val &= ~S_CMD_DONE_EN;
-	writel_relaxed(val, se->base + SE_GENI_S_IRQ_EN);
+		if (val != val_old)
+			writel_relaxed(val, se->base + SE_GENI_S_IRQ_EN);
+	}
 
-	val = readl_relaxed(se->base + SE_GENI_DMA_MODE_EN);
+	val_old = val = readl_relaxed(se->base + SE_GENI_DMA_MODE_EN);
 	val |= GENI_DMA_MODE_EN;
-	writel_relaxed(val, se->base + SE_GENI_DMA_MODE_EN);
+	if (val != val_old)
+		writel_relaxed(val, se->base + SE_GENI_DMA_MODE_EN);
 }
 
 /**
-- 
2.28.0.1011.ga647a8990f-goog