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From: Frank Li <Frank.Li@nxp.com>
To: gustavo.pimentel@synopsys.com, hongxing.zhu@nxp.com,
	l.stach@pengutronix.de, linux-imx@nxp.com,
	linux-pci@vger.kernel.org, dmaengine@vger.kernel.org,
	fancer.lancer@gmail.com, lznuaa@gmail.com, helgaas@kernel.org
Cc: vkoul@kernel.org, lorenzo.pieralisi@arm.com, robh@kernel.org,
	kw@linux.com, bhelgaas@google.com,
	manivannan.sadhasivam@linaro.org,
	Sergey.Semin@baikalelectronics.ru
Subject: [PATCH v10 5/9] dmaengine: dw-edma: Drop dma_slave_config.direction field usage
Date: Mon,  2 May 2022 19:57:57 -0500	[thread overview]
Message-ID: <20220503005801.1714345-6-Frank.Li@nxp.com> (raw)
In-Reply-To: <20220503005801.1714345-1-Frank.Li@nxp.com>

From: Serge Semin <Sergey.Semin@baikalelectronics.ru>

The dma_slave_config.direction field usage in the DW eDMA driver has been
introduced in the commit bd96f1b2f43a ("dmaengine: dw-edma: support local
dma device transfer semantics"). Mainly the change introduced there was
correct (indeed DEV_TO_MEM means using RD-channel and MEM_TO_DEV -
WR-channel for the case of having eDMA accessed locally from
CPU/Application side), but providing an additional
MEM_TO_MEM/DEV_TO_DEV-based semantics was quite redundant if not to say
potentially harmful (when it comes to removing the denoted field). First
of all since the dma_slave_config.direction field has been marked as
obsolete (see [1] and the structure dc [2]) and will be discarded in
future, using it especially in a non-standard way is discouraged. Secondly
in accordance with the commit denoted above the default
dw_edma_device_transfer() semantics has been changed despite what it's
message said. So claiming that the method was left backward compatible was
wrong.

Anyway let's fix the problems denoted above and simplify the
dw_edma_device_transfer() method by dropping the parsing of the
DMA-channel direction field. Instead of having that implicit
dma_slave_config.direction field semantic we can use the recently added
DW_EDMA_CHIP_LOCAL flag to distinguish between the local and remote DW
eDMA setups thus preserving both cases support. In addition to that an
ASCII-figure has been added to clarify the complication out.

[1] Documentation/driver-api/dmaengine/provider.rst
[2] include/linux/dmaengine.h: dma_slave_config.direction

Co-developed-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
Signed-off-by: Serge Semin <Sergey.Semin@baikalelectronics.ru>
Signed-off-by: Frank Li <Frank.Li@nxp.com>
---
 drivers/dma/dw-edma/dw-edma-core.c | 49 +++++++++++++++++++++---------
 1 file changed, 34 insertions(+), 15 deletions(-)

diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
index 1ef326f7151a3..3ce0d7600da64 100644
--- a/drivers/dma/dw-edma/dw-edma-core.c
+++ b/drivers/dma/dw-edma/dw-edma-core.c
@@ -340,21 +340,40 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer)
 	if (!chan->configured)
 		return NULL;
 
-	switch (chan->config.direction) {
-	case DMA_DEV_TO_MEM: /* local DMA */
-		if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_READ)
-			break;
-		return NULL;
-	case DMA_MEM_TO_DEV: /* local DMA */
-		if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_WRITE)
-			break;
-		return NULL;
-	default: /* remote DMA */
-		if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_READ)
-			break;
-		if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_WRITE)
-			break;
-		return NULL;
+	/*
+	 * Local Root Port/End-point              Remote End-point
+	 * +-----------------------+ PCIe bus +----------------------+
+	 * |                       |    +-+   |                      |
+	 * |    DEV_TO_MEM   Rx Ch <----+ +---+ Tx Ch  DEV_TO_MEM    |
+	 * |                       |    | |   |                      |
+	 * |    MEM_TO_DEV   Tx Ch +----+ +---> Rx Ch  MEM_TO_DEV    |
+	 * |                       |    +-+   |                      |
+	 * +-----------------------+          +----------------------+
+	 *
+	 * 1. Normal logic:
+	 * If eDMA is embedded into the DW PCIe RP/EP and controlled from the
+	 * CPU/Application side, the Rx channel (EDMA_DIR_READ) will be used
+	 * for the device read operations (DEV_TO_MEM) and the Tx channel
+	 * (EDMA_DIR_WRITE) - for the write operations (MEM_TO_DEV).
+	 *
+	 * 2. Inverted logic:
+	 * If eDMA is embedded into a Remote PCIe EP and is controlled by the
+	 * MWr/MRd TLPs sent from the CPU's PCIe host controller, the Tx
+	 * channel (EDMA_DIR_WRITE) will be used for the device read operations
+	 * (DEV_TO_MEM) and the Rx channel (EDMA_DIR_READ) - for the write
+	 * operations (MEM_TO_DEV).
+	 *
+	 * It is the client driver responsibility to choose a proper channel
+	 * for the DMA transfers.
+	 */
+	if (chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL) {
+		if ((chan->dir == EDMA_DIR_READ && dir != DMA_DEV_TO_MEM) ||
+		    (chan->dir == EDMA_DIR_WRITE && dir != DMA_MEM_TO_DEV))
+			return NULL;
+	} else {
+		if ((chan->dir == EDMA_DIR_WRITE && dir != DMA_DEV_TO_MEM) ||
+		    (chan->dir == EDMA_DIR_READ && dir != DMA_MEM_TO_DEV))
+			return NULL;
 	}
 
 	if (xfer->type == EDMA_XFER_CYCLIC) {
-- 
2.35.1


  parent reply	other threads:[~2022-05-03  1:05 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-05-03  0:57 [PATCH v10 0/9] Enable designware PCI EP EDMA locally Frank Li
2022-05-03  0:57 ` [PATCH v10 1/9] dmaengine: dw-edma: Remove unused field irq in struct dw_edma_chip Frank Li
2022-05-03  0:57 ` [PATCH v10 2/9] dmaengine: dw-edma: Detach the private data and chip info structures Frank Li
2022-05-03  0:57 ` [PATCH v10 3/9] dmaengine: dw-edma: Change rg_region to reg_base in struct dw_edma_chip Frank Li
2022-05-03  0:57 ` [PATCH v10 4/9] dmaengine: dw-edma: Rename wr(rd)_ch_cnt to ll_wr(rd)_cnt " Frank Li
2022-05-03  0:57 ` Frank Li [this message]
2022-05-03  0:57 ` [PATCH v10 6/9] dmaengine: dw-edma: Fix eDMA Rd/Wr-channels and DMA-direction semantics Frank Li
2022-05-03  0:57 ` [PATCH v10 7/9] dmaengine: dw-edma: Add support for chip specific flags Frank Li
2022-05-03  0:58 ` [PATCH v10 8/9] dmaengine: dw-edma: Add DW_EDMA_CHIP_32BIT_DBI " Frank Li
2022-05-04 18:43   ` Zhi Li
2022-05-03  0:58 ` [PATCH v10 9/9] PCI: endpoint: Enable DMA controller tests for endpoints with DMA capabilities Frank Li
2022-05-04 19:34   ` Zhi Li
2022-05-11  9:28   ` Lorenzo Pieralisi
2022-05-11 16:18     ` Zhi Li
2022-05-11 17:30       ` Lorenzo Pieralisi
2022-05-11 19:12         ` Zhi Li
2022-05-13  0:48           ` Zhi Li
2022-05-12 13:51   ` Kishon Vijay Abraham I
2022-05-12 15:36     ` Zhi Li
2022-05-03 23:18 ` [PATCH v10 0/9] Enable designware PCI EP EDMA locally Serge Semin
2022-05-10 17:47   ` Lorenzo Pieralisi
2022-05-10 18:02     ` Zhi Li
2022-05-12  0:04     ` Serge Semin
2022-05-12 14:14 ` Manivannan Sadhasivam

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