linux-kernel - [PATCH 6.1.y] dmaengine: dw-edma: eDMA: Add sync read before starting the DMA transfer in remote setup

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Message-ID: <20241211100409.2069734-1-jianqi.ren.cn@windriver.com>
Date: Wed, 11 Dec 2024 18:04:09 +0800
From: <jianqi.ren.cn@...driver.com>
To: <kory.maincent@...tlin.com>, <gregkh@...uxfoundation.org>
CC: <patches@...ts.linux.dev>, <fancer.lancer@...il.com>,
        <manivannan.sadhasivam@...aro.org>, <vkoul@...nel.org>,
        <stable@...r.kernel.org>, <gustavo.pimentel@...opsys.com>,
        <dmaengine@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: [PATCH 6.1.y] dmaengine: dw-edma: eDMA: Add sync read before starting the DMA transfer in remote setup

From: Kory Maincent <kory.maincent@...tlin.com>

[ Upstream commit bbcc1c83f343e580c3aa1f2a8593343bf7b55bba ]

The Linked list element and pointer are not stored in the same memory as
the eDMA controller register. If the doorbell register is toggled before
the full write of the linked list a race condition error will occur.
In remote setup we can only use a readl to the memory to assure the full
write has occurred.

Fixes: 7e4b8a4fbe2c ("dmaengine: Add Synopsys eDMA IP version 0 support")
Reviewed-by: Serge Semin <fancer.lancer@...il.com>
Reviewed-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
Link: https://lore.kernel.org/r/20240129-b4-feature_hdma_mainline-v7-6-8e8c1acb7a46@bootlin.com
Signed-off-by: Vinod Koul <vkoul@...nel.org>
Signed-off-by: Jianqi Ren <jianqi.ren.cn@...driver.com>
---
 drivers/dma/dw-edma/dw-edma-v0-core.c | 17 +++++++++++++++++
 1 file changed, 17 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-edma-v0-core.c b/drivers/dma/dw-edma/dw-edma-v0-core.c
index a3816ba63285..aeaae28fab85 100644
--- a/drivers/dma/dw-edma/dw-edma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-edma-v0-core.c
@@ -357,6 +357,20 @@ static void dw_edma_v0_core_write_chunk(struct dw_edma_chunk *chunk)
 	#endif /* CONFIG_64BIT */
 }
 
+static void dw_edma_v0_sync_ll_data(struct dw_edma_chunk *chunk)
+{
+	/*
+	 * In case of remote eDMA engine setup, the DW PCIe RP/EP internal
+	 * configuration registers and application memory are normally accessed
+	 * over different buses. Ensure LL-data reaches the memory before the
+	 * doorbell register is toggled by issuing the dummy-read from the remote
+	 * LL memory in a hope that the MRd TLP will return only after the
+	 * last MWr TLP is completed
+	 */
+	if (!(chunk->chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+		readl(chunk->ll_region.vaddr);
+}
+
 void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
 {
 	struct dw_edma_chan *chan = chunk->chan;
@@ -423,6 +437,9 @@ void dw_edma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
 		SET_CH_32(dw, chan->dir, chan->id, llp.msb,
 			  upper_32_bits(chunk->ll_region.paddr));
 	}
+
+	dw_edma_v0_sync_ll_data(chunk);
+
 	/* Doorbell */
 	SET_RW_32(dw, chan->dir, doorbell,
 		  FIELD_PREP(EDMA_V0_DOORBELL_CH_MASK, chan->id));
-- 
2.39.4