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From: Serge Semin <Sergey.Semin@baikalelectronics.ru>
To: Mark Brown <broonie@kernel.org>, Feng Tang <feng.tang@intel.com>,
	Alan Cox <alan@linux.intel.com>,
	Linus Walleij <linus.walleij@stericsson.com>,
	Vinod Koul <vkoul@kernel.org>,
	Grant Likely <grant.likely@secretlab.ca>
Cc: Serge Semin <Sergey.Semin@baikalelectronics.ru>,
	Serge Semin <fancer.lancer@gmail.com>,
	Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>,
	Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>,
	Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>,
	Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
	Arnd Bergmann <arnd@arndb.de>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	Rob Herring <robh+dt@kernel.org>, <linux-mips@vger.kernel.org>,
	<devicetree@vger.kernel.org>, <linux-spi@vger.kernel.org>,
	<linux-kernel@vger.kernel.org>
Subject: [PATCH v6 05/16] spi: dw: Add SPI Rx-done wait method to DMA-based transfer
Date: Fri, 29 May 2020 16:11:54 +0300
Message-ID: <20200529131205.31838-6-Sergey.Semin@baikalelectronics.ru> (raw)
In-Reply-To: <20200529131205.31838-1-Sergey.Semin@baikalelectronics.ru>

Having any data left in the Rx FIFO after the DMA engine claimed it has
finished all DMA transactions is an abnormal situation, since the DW SPI
controller driver expects to have all the data being fetched and placed
into the SPI Rx buffer at that moment. In case if that has happened we
hopefully assume that the DMA engine may still be doing the data fetching,
thus we give it sometime to finish. If after a short period of time the
data is still left in the Rx FIFO, the driver will give up waiting and
return an error indicating that the SPI controller/DMA engine must have
hung up or failed at some point of doing their duties.

Fixes: 7063c0d942a1 ("spi/dw_spi: add DMA support")
Co-developed-by: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Signed-off-by: Georgy Vlasov <Georgy.Vlasov@baikalelectronics.ru>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Cc: Ramil Zaripov <Ramil.Zaripov@baikalelectronics.ru>
Cc: Alexey Malahov <Alexey.Malahov@baikalelectronics.ru>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Feng Tang <feng.tang@intel.com>
Cc: Rob Herring <robh+dt@kernel.org>
Cc: linux-mips@vger.kernel.org
Cc: devicetree@vger.kernel.org

---

Changelog v5:
- Create a dedicated patch which adds the Rx-done wait method.
- Add more detailed description of the problem the patch fixes.
- Wait for the SPI Rx transfer finish in the mid_spi_dma_transfer() method
  executed in the task context.
- Use spi_delay_exec() to wait for the SPI Rx completion, since now the
  driver does in the kernel thread context.
- Wait for a delay correlated with the APB/SSI synchronous clock rate
  instead of using the SPI bus clock rate.

Changelog v6:
- Calculate the delay with better accuracy by moving 4-multiplication
  to the head of the formulae:
  ns = 4U * NSEC_PER_SEC / dws->max_freq * nents.
---
 drivers/spi/spi-dw-mid.c | 48 +++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/drivers/spi/spi-dw-mid.c b/drivers/spi/spi-dw-mid.c
index 846e3db91329..abd6955ad1f7 100644
--- a/drivers/spi/spi-dw-mid.c
+++ b/drivers/spi/spi-dw-mid.c
@@ -248,6 +248,49 @@ static struct dma_async_tx_descriptor *dw_spi_dma_prepare_tx(struct dw_spi *dws,
 	return txdesc;
 }
 
+static inline bool dw_spi_dma_rx_busy(struct dw_spi *dws)
+{
+	return !!(dw_readl(dws, DW_SPI_SR) & SR_RF_NOT_EMPT);
+}
+
+static int dw_spi_dma_wait_rx_done(struct dw_spi *dws)
+{
+	int retry = WAIT_RETRIES;
+	struct spi_delay delay;
+	unsigned long ns, us;
+	u32 nents;
+
+	/*
+	 * It's unlikely that DMA engine is still doing the data fetching, but
+	 * if it's let's give it some reasonable time. The timeout calculation
+	 * is based on the synchronous APB/SSI reference clock rate, on a
+	 * number of data entries left in the Rx FIFO, times a number of clock
+	 * periods normally needed for a single APB read/write transaction
+	 * without PREADY signal utilized (which is true for the DW APB SSI
+	 * controller).
+	 */
+	nents = dw_readl(dws, DW_SPI_RXFLR);
+	ns = 4U * NSEC_PER_SEC / dws->max_freq * nents;
+	if (ns <= NSEC_PER_USEC) {
+		delay.unit = SPI_DELAY_UNIT_NSECS;
+		delay.value = ns;
+	} else {
+		us = DIV_ROUND_UP(ns, NSEC_PER_USEC);
+		delay.unit = SPI_DELAY_UNIT_USECS;
+		delay.value = clamp_val(us, 0, USHRT_MAX);
+	}
+
+	while (dw_spi_dma_rx_busy(dws) && retry--)
+		spi_delay_exec(&delay, NULL);
+
+	if (retry < 0) {
+		dev_err(&dws->master->dev, "Rx hanged up\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
 /*
  * dws->dma_chan_busy is set before the dma transfer starts, callback for rx
  * channel will clear a corresponding bit.
@@ -358,7 +401,10 @@ static int mid_spi_dma_transfer(struct dw_spi *dws, struct spi_transfer *xfer)
 			return ret;
 	}
 
-	return 0;
+	if (rxdesc && dws->master->cur_msg->status == -EINPROGRESS)
+		ret = dw_spi_dma_wait_rx_done(dws);
+
+	return ret;
 }
 
 static void mid_spi_dma_stop(struct dw_spi *dws)
-- 
2.26.2


  parent reply index

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-05-29 13:11 [PATCH v6 00/16] spi: dw: Add generic DW DMA controller support Serge Semin
2020-05-29 13:11 ` [PATCH v6 01/16] spi: dw: Set xfer effective_speed_hz Serge Semin
2020-05-29 13:11 ` [PATCH v6 02/16] spi: dw: Return any value retrieved from the dma_transfer callback Serge Semin
2020-05-29 13:11 ` [PATCH v6 03/16] spi: dw: Locally wait for the DMA transfers completion Serge Semin
2020-05-29 13:11 ` [PATCH v6 04/16] spi: dw: Add SPI Tx-done wait method to DMA-based transfer Serge Semin
2020-05-29 13:11 ` Serge Semin [this message]
2020-05-29 13:11 ` [PATCH v6 06/16] spi: dw: Parameterize the DMA Rx/Tx burst length Serge Semin
2020-05-29 13:11 ` [PATCH v6 07/16] spi: dw: Use DMA max burst to set the request thresholds Serge Semin
2020-05-29 13:11 ` [PATCH v6 08/16] spi: dw: Fix Rx-only DMA transfers Serge Semin
2020-05-29 13:11 ` [PATCH v6 09/16] spi: dw: Add core suffix to the DW APB SSI core source file Serge Semin
2020-05-29 13:11 ` [PATCH v6 10/16] spi: dw: Move Non-DMA code to the DW PCIe-SPI driver Serge Semin
2020-05-29 13:12 ` [PATCH v6 11/16] spi: dw: Remove DW DMA code dependency from DW_DMAC_PCI Serge Semin
2020-05-29 13:12 ` [PATCH v6 12/16] spi: dw: Add DW SPI DMA/PCI/MMIO dependency on the DW SPI core Serge Semin
2020-05-29 13:12 ` [PATCH v6 13/16] spi: dw: Cleanup generic DW DMA code namings Serge Semin
2020-05-29 13:12 ` [PATCH v6 14/16] spi: dw: Add DMA support to the DW SPI MMIO driver Serge Semin
2020-05-29 13:12 ` [PATCH v6 15/16] spi: dw: Use regset32 DebugFS method to create regdump file Serge Semin
2020-05-29 13:12 ` [PATCH v6 16/16] dt-bindings: spi: Convert DW SPI binding to DT schema Serge Semin
2020-05-29 13:27 ` [PATCH v6 00/16] spi: dw: Add generic DW DMA controller support Andy Shevchenko
2020-05-29 17:18 ` Mark Brown
2020-05-29 17:26   ` Serge Semin
2020-05-29 17:33     ` Mark Brown
2020-05-29 17:35       ` Serge Semin
2020-05-29 21:22       ` Rob Herring
2020-05-29 22:21         ` Mark Brown
2020-05-29 17:43     ` Andy Shevchenko
2020-05-29 17:47       ` Serge Semin

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