linux-kernel - [PATCH 3/5] dmaengine: jz4780: Work around hardware bug on JZ4760 SoCs

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Date:   Mon, 11 Oct 2021 16:36:50 +0200
From:   Paul Cercueil <paul@...pouillou.net>
To:     Vinod Koul <vkoul@...nel.org>, Rob Herring <robh+dt@...nel.org>
Cc:     list@...ndingux.net, dmaengine@...r.kernel.org,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-mips@...r.kernel.org, Paul Cercueil <paul@...pouillou.net>
Subject: [PATCH 3/5] dmaengine: jz4780: Work around hardware bug on JZ4760 SoCs

The JZ4760 SoC has a hardware problem with chan0 not enabling properly
if it's enabled before chan1, after a reset (works fine afterwards).
This is worked around in the probe function by just enabling then
disabling chan1.

Signed-off-by: Paul Cercueil <paul@...pouillou.net>
---
 drivers/dma/dma-jz4780.c | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/drivers/dma/dma-jz4780.c b/drivers/dma/dma-jz4780.c
index ebee94dbd630..d71bc7235959 100644
--- a/drivers/dma/dma-jz4780.c
+++ b/drivers/dma/dma-jz4780.c
@@ -937,6 +937,14 @@ static int jz4780_dma_probe(struct platform_device *pdev)
 		jzchan->vchan.desc_free = jz4780_dma_desc_free;
 	}
 
+	/*
+	 * On JZ4760, chan0 won't enable properly the first time.
+	 * Enabling then disabling chan1 will magically make chan0 work
+	 * correctly.
+	 */
+	jz4780_dma_chan_enable(jzdma, 1);
+	jz4780_dma_chan_disable(jzdma, 1);
+
 	ret = platform_get_irq(pdev, 0);
 	if (ret < 0)
 		goto err_disable_clk;
-- 
2.33.0