linux-kernel - [PATCH 4/9] dmaengine: dw-edma: HDMA: Add memory barrier before starting the DMA transfer in remote setup

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Message-Id: <20230609081654.330857-5-kory.maincent@bootlin.com>
Date:   Fri,  9 Jun 2023 10:16:49 +0200
From:   Köry Maincent <kory.maincent@...tlin.com>
To:     Cai Huoqing <cai.huoqing@...ux.dev>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Serge Semin <fancer.lancer@...il.com>,
        Vinod Koul <vkoul@...nel.org>,
        Gustavo Pimentel <Gustavo.Pimentel@...opsys.com>,
        dmaengine@...r.kernel.org, linux-kernel@...r.kernel.org
Cc:     Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>,
        Herve Codina <herve.codina@...tlin.com>,
        Kory Maincent <kory.maincent@...tlin.com>
Subject: [PATCH 4/9] dmaengine: dw-edma: HDMA: Add memory barrier before starting the DMA transfer in remote setup

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

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

Fixes: e74c39573d35 ("dmaengine: dw-edma: Add support for native HDMA")
Signed-off-by: Kory Maincent <kory.maincent@...tlin.com>
---

This patch is fixing a commit which is only in dmaengine tree and not
merged mainline.
---
 drivers/dma/dw-edma/dw-hdma-v0-core.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/dma/dw-edma/dw-hdma-v0-core.c b/drivers/dma/dw-edma/dw-hdma-v0-core.c
index 7bd1a0f742be..0b77ddbe91b5 100644
--- a/drivers/dma/dw-edma/dw-hdma-v0-core.c
+++ b/drivers/dma/dw-edma/dw-hdma-v0-core.c
@@ -247,6 +247,15 @@ static void dw_hdma_v0_core_start(struct dw_edma_chunk *chunk, bool first)
 	/* Set consumer cycle */
 	SET_CH_32(dw, chan->dir, chan->id, cycle_sync,
 		  HDMA_V0_CONSUMER_CYCLE_STAT | HDMA_V0_CONSUMER_CYCLE_BIT);
+
+	if (!(chunk->chan->dw->chip->flags & DW_EDMA_CHIP_LOCAL))
+		/* Make sure Linked List has been written.
+		 * Linux memory barriers don't cater for what's required here.
+		 * What's required is what's here - a read of the linked
+		 * list region.
+		 */
+		readl(chunk->ll_region.vaddr.io);
+
 	/* Doorbell */
 	SET_CH_32(dw, chan->dir, chan->id, doorbell, HDMA_V0_DOORBELL_START);
 }
-- 
2.25.1