linux-kernel - [PATCH 08/18] spi: stm32h7: fix dbg/warn/err conditions in irq handler

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Date:   Wed, 5 Aug 2020 09:02:03 +0200
From:   Alain Volmat <alain.volmat@...com>
To:     <broonie@...nel.org>, <amelie.delaunay@...com>
CC:     <mcoquelin.stm32@...il.com>, <alexandre.torgue@...com>,
        <linux-spi@...r.kernel.org>,
        <linux-stm32@...md-mailman.stormreply.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <fabrice.gasnier@...com>,
        <alain.volmat@...com>
Subject: [PATCH 08/18] spi: stm32h7: fix dbg/warn/err conditions in irq handler

From: Amelie Delaunay <amelie.delaunay@...com>

Make spurious interrupts visible. We do not expect to receive
them, so rise at least a warning if it happens.

Don't bother repeating the suspended RX messages; to avoid RX
overrun we have set SPI_CR1_MASRX that enables the automatic
suspended RX so, mainly in irq mode, it's normal that we will
receive SUSP interrupts every time the CPU is too much loaded
or the spi speed too high and we fail to remove on-time the
data from the RX queue. Moreover, when the CPU is overloaded
there is a delay while serving the interrupt. This forces
inactivity on the SPI bus between bytes. So the warning message
"System too slow, spi speed not guaranteed" is inaccurate; the
term "spi speed" is currently used in kernel for the toggling
frequency of the spi CLK pin, which is driven by HW and is not
impacted by CPU overload. The correct term should be
"data throughput".

RX overrun is an error condition that signals a corrupted RX
stream both in dma and in irq modes. Report the error and
abort the transfer in either cases.

Signed-off-by: Amelie Delaunay <amelie.delaunay@...com>
Signed-off-by: Antonio Borneo <antonio.borneo@...com>
Signed-off-by: Alain Volmat <alain.volmat@...com>
---
 drivers/spi/spi-stm32.c | 19 +++++++------------
 1 file changed, 7 insertions(+), 12 deletions(-)

diff --git a/drivers/spi/spi-stm32.c b/drivers/spi/spi-stm32.c
index 06478643855a..6731e3ff0e50 100644
--- a/drivers/spi/spi-stm32.c
+++ b/drivers/spi/spi-stm32.c
@@ -904,14 +904,16 @@ static irqreturn_t stm32h7_spi_irq_thread(int irq, void *dev_id)
 	mask &= sr;

 	if (!mask) {
-		dev_dbg(spi->dev, "spurious IT (sr=0x%08x, ier=0x%08x)\n",
-			sr, ier);
+		dev_warn(spi->dev, "spurious IT (sr=0x%08x, ier=0x%08x)\n",
+			 sr, ier);
 		spin_unlock_irqrestore(&spi->lock, flags);
 		return IRQ_NONE;
 	}

 	if (mask & STM32H7_SPI_SR_SUSP) {
-		dev_warn(spi->dev, "Communication suspended\n");
+		dev_warn_once(spi->dev,
+			      "System too slow is limiting data throughput\n");
+
 		if (!spi->cur_usedma && (spi->rx_buf && (spi->rx_len > 0)))
 			stm32h7_spi_read_rxfifo(spi);
 		/*
@@ -924,15 +926,8 @@ static irqreturn_t stm32h7_spi_irq_thread(int irq, void *dev_id)
 	}

 	if (mask & STM32H7_SPI_SR_OVR) {
-		dev_warn(spi->dev, "Overrun: received value discarded\n");
-		if (!spi->cur_usedma && (spi->rx_buf && (spi->rx_len > 0)))
-			stm32h7_spi_read_rxfifo(spi);
-		/*
-		 * If overrun is detected while using DMA, it means that
-		 * something went wrong, so stop the current transfer
-		 */
-		if (spi->cur_usedma)
-			end = true;
+		dev_err(spi->dev, "Overrun: RX data lost\n");
+		end = true;
 		ifcr |= STM32H7_SPI_SR_OVR;
 	}

-- 
2.7.4