linux-kernel - [PATCH v2 13/32] dmaengine: at_hdmac: Don't allow CPU to reorder channel enable

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Message-ID: <20221025090306.297886-14-tudor.ambarus@microchip.com>
Date:   Tue, 25 Oct 2022 12:02:47 +0300
From:   Tudor Ambarus <tudor.ambarus@...rochip.com>
To:     <vkoul@...nel.org>, <peda@...ntia.se>, <du@...ntia.se>
CC:     <maciej.sosnowski@...el.com>, <nicolas.ferre@...rochip.com>,
        <mripard@...nel.org>, <torfl6749@...il.com>,
        <linux-kernel@...r.kernel.org>, <dmaengine@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        "Tudor Ambarus" <tudor.ambarus@...rochip.com>,
        <stable@...r.kernel.org>
Subject: [PATCH v2 13/32] dmaengine: at_hdmac: Don't allow CPU to reorder channel enable

at_hdmac uses __raw_writel for register writes. In the absence of a
barrier, the CPU may reorder the register operations.
Introduce a write memory barrier so that the CPU does not reorder the
channel enable, thus the start of the transfer, without making sure that
all the pre-required register fields are already written.

Fixes: dc78baa2b90b ("dmaengine: at_hdmac: new driver for the Atmel AHB DMA Controller")
Reported-by: Peter Rosin <peda@...ntia.se>
Signed-off-by: Tudor Ambarus <tudor.ambarus@...rochip.com>
Cc: stable@...r.kernel.org
Link: https://lore.kernel.org/lkml/13c6c9a2-6db5-c3bf-349b-4c127ad3496a@axentia.se/
---
 drivers/dma/at_hdmac.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/drivers/dma/at_hdmac.c b/drivers/dma/at_hdmac.c
index 80eeb4fb88ef..968a5aba47cd 100644
--- a/drivers/dma/at_hdmac.c
+++ b/drivers/dma/at_hdmac.c
@@ -256,6 +256,8 @@ static void atc_dostart(struct at_dma_chan *atchan, struct at_desc *first)
 		       ATC_SPIP_BOUNDARY(first->boundary));
 	channel_writel(atchan, DPIP, ATC_DPIP_HOLE(first->dst_hole) |
 		       ATC_DPIP_BOUNDARY(first->boundary));
+	/* Don't allow CPU to reorder channel enable. */
+	wmb();
 	dma_writel(atdma, CHER, atchan->mask);
 
 	vdbg_dump_regs(atchan);
-- 
2.25.1